107 files changed, 3109 insertions, 2061 deletions
diff --git a/py/asmarm.c b/py/asmarm.c
index 552fdfb34..1a8923bc2 100644
--- a/py/asmarm.c
+++ b/py/asmarm.c
@@ -150,10 +150,7 @@ void asm_arm_bkpt(asm_arm_t *as) {
 //  | low address    | high address in RAM
 
 void asm_arm_entry(asm_arm_t *as, int num_locals) {
-
-    if (num_locals < 0) {
-        num_locals = 0;
-    }
+    assert(num_locals >= 0);
 
     as->stack_adjust = 0;
     as->push_reglist = 1 << ASM_ARM_REG_R1
diff --git a/py/asmarm.h b/py/asmarm.h
index 9392a0fae..fbfe09aac 100644
--- a/py/asmarm.h
+++ b/py/asmarm.h
@@ -167,17 +167,12 @@ void asm_arm_bl_ind(asm_arm_t *as, void *fun_ptr, uint fun_id, uint reg_temp);
     } while (0)
 #define ASM_CALL_IND(as, ptr, idx) asm_arm_bl_ind(as, ptr, idx, ASM_ARM_REG_R3)
 
-#define ASM_MOV_REG_TO_LOCAL(as, reg, local_num) asm_arm_mov_local_reg(as, (local_num), (reg))
-#define ASM_MOV_IMM_TO_REG(as, imm, reg) asm_arm_mov_reg_i32(as, (reg), (imm))
-#define ASM_MOV_ALIGNED_IMM_TO_REG(as, imm, reg) asm_arm_mov_reg_i32(as, (reg), (imm))
-#define ASM_MOV_IMM_TO_LOCAL_USING(as, imm, local_num, reg_temp) \
-    do { \
-        asm_arm_mov_reg_i32(as, (reg_temp), (imm)); \
-        asm_arm_mov_local_reg(as, (local_num), (reg_temp)); \
-    } while (false)
-#define ASM_MOV_LOCAL_TO_REG(as, local_num, reg) asm_arm_mov_reg_local(as, (reg), (local_num))
+#define ASM_MOV_LOCAL_REG(as, local_num, reg_src) asm_arm_mov_local_reg((as), (local_num), (reg_src))
+#define ASM_MOV_REG_IMM(as, reg_dest, imm) asm_arm_mov_reg_i32((as), (reg_dest), (imm))
+#define ASM_MOV_REG_ALIGNED_IMM(as, reg_dest, imm) asm_arm_mov_reg_i32((as), (reg_dest), (imm))
+#define ASM_MOV_REG_LOCAL(as, reg_dest, local_num) asm_arm_mov_reg_local((as), (reg_dest), (local_num))
 #define ASM_MOV_REG_REG(as, reg_dest, reg_src) asm_arm_mov_reg_reg((as), (reg_dest), (reg_src))
-#define ASM_MOV_LOCAL_ADDR_TO_REG(as, local_num, reg) asm_arm_mov_reg_local_addr(as, (reg), (local_num))
+#define ASM_MOV_REG_LOCAL_ADDR(as, reg_dest, local_num) asm_arm_mov_reg_local_addr((as), (reg_dest), (local_num))
 
 #define ASM_LSL_REG_REG(as, reg_dest, reg_shift) asm_arm_lsl_reg_reg((as), (reg_dest), (reg_shift))
 #define ASM_ASR_REG_REG(as, reg_dest, reg_shift) asm_arm_asr_reg_reg((as), (reg_dest), (reg_shift))
diff --git a/py/asmbase.c b/py/asmbase.c
index c941e917b..4c84c3b25 100644
--- a/py/asmbase.c
+++ b/py/asmbase.c
@@ -46,10 +46,10 @@ void mp_asm_base_deinit(mp_asm_base_t *as, bool free_code) {
 }
 
 void mp_asm_base_start_pass(mp_asm_base_t *as, int pass) {
-    if (pass == MP_ASM_PASS_COMPUTE) {
-        // reset all labels
+    if (pass < MP_ASM_PASS_EMIT) {
+        // Reset labels so we can detect backwards jumps (and verify unique assignment)
         memset(as->label_offsets, -1, as->max_num_labels * sizeof(size_t));
-    } else if (pass == MP_ASM_PASS_EMIT) {
+    } else {
         // allocating executable RAM is platform specific
         MP_PLAT_ALLOC_EXEC(as->code_offset, (void**)&as->code_base, &as->code_size);
         assert(as->code_base != NULL);
diff --git a/py/asmthumb.c b/py/asmthumb.c
index 5316a7efb..c5b45f2f5 100644
--- a/py/asmthumb.c
+++ b/py/asmthumb.c
@@ -104,6 +104,8 @@ STATIC void asm_thumb_write_word32(asm_thumb_t *as, int w32) {
 //  | low address    | high address in RAM
 
 void asm_thumb_entry(asm_thumb_t *as, int num_locals) {
+    assert(num_locals >= 0);
+
     // work out what to push and how many extra spaces to reserve on stack
     // so that we have enough for all locals and it's aligned an 8-byte boundary
     // we push extra regs (r1, r2, r3) to help do the stack adjustment
@@ -111,9 +113,6 @@ void asm_thumb_entry(asm_thumb_t *as, int num_locals) {
     // for push rlist, lowest numbered register at the lowest address
     uint reglist;
     uint stack_adjust;
-    if (num_locals < 0) {
-        num_locals = 0;
-    }
     // don't pop r0 because it's used for return value
     switch (num_locals) {
         case 0:
diff --git a/py/asmthumb.h b/py/asmthumb.h
index a19c11b2c..f8665f35c 100644
--- a/py/asmthumb.h
+++ b/py/asmthumb.h
@@ -26,6 +26,7 @@
 #ifndef MICROPY_INCLUDED_PY_ASMTHUMB_H
 #define MICROPY_INCLUDED_PY_ASMTHUMB_H
 
+#include <assert.h>
 #include "py/misc.h"
 #include "py/asmbase.h"
 
@@ -283,17 +284,12 @@ void asm_thumb_bl_ind(asm_thumb_t *as, void *fun_ptr, uint fun_id, uint reg_temp
     } while (0)
 #define ASM_CALL_IND(as, ptr, idx) asm_thumb_bl_ind(as, ptr, idx, ASM_THUMB_REG_R3)
 
-#define ASM_MOV_REG_TO_LOCAL(as, reg, local_num) asm_thumb_mov_local_reg(as, (local_num), (reg))
-#define ASM_MOV_IMM_TO_REG(as, imm, reg) asm_thumb_mov_reg_i32_optimised(as, (reg), (imm))
-#define ASM_MOV_ALIGNED_IMM_TO_REG(as, imm, reg) asm_thumb_mov_reg_i32_aligned(as, (reg), (imm))
-#define ASM_MOV_IMM_TO_LOCAL_USING(as, imm, local_num, reg_temp) \
-    do { \
-        asm_thumb_mov_reg_i32_optimised(as, (reg_temp), (imm)); \
-        asm_thumb_mov_local_reg(as, (local_num), (reg_temp)); \
-    } while (false)
-#define ASM_MOV_LOCAL_TO_REG(as, local_num, reg) asm_thumb_mov_reg_local(as, (reg), (local_num))
+#define ASM_MOV_LOCAL_REG(as, local_num, reg) asm_thumb_mov_local_reg((as), (local_num), (reg))
+#define ASM_MOV_REG_IMM(as, reg_dest, imm) asm_thumb_mov_reg_i32_optimised((as), (reg_dest), (imm))
+#define ASM_MOV_REG_ALIGNED_IMM(as, reg_dest, imm) asm_thumb_mov_reg_i32_aligned((as), (reg_dest), (imm))
+#define ASM_MOV_REG_LOCAL(as, reg_dest, local_num) asm_thumb_mov_reg_local((as), (reg_dest), (local_num))
 #define ASM_MOV_REG_REG(as, reg_dest, reg_src) asm_thumb_mov_reg_reg((as), (reg_dest), (reg_src))
-#define ASM_MOV_LOCAL_ADDR_TO_REG(as, local_num, reg) asm_thumb_mov_reg_local_addr(as, (reg), (local_num))
+#define ASM_MOV_REG_LOCAL_ADDR(as, reg_dest, local_num) asm_thumb_mov_reg_local_addr((as), (reg_dest), (local_num))
 
 #define ASM_LSL_REG_REG(as, reg_dest, reg_shift) asm_thumb_format_4((as), ASM_THUMB_FORMAT_4_LSL, (reg_dest), (reg_shift))
 #define ASM_ASR_REG_REG(as, reg_dest, reg_shift) asm_thumb_format_4((as), ASM_THUMB_FORMAT_4_ASR, (reg_dest), (reg_shift))
diff --git a/py/asmx64.c b/py/asmx64.c
index aa2a8ec7c..c900a08d1 100644
--- a/py/asmx64.c
+++ b/py/asmx64.c
@@ -526,11 +526,9 @@ void asm_x64_jcc_label(asm_x64_t *as, int jcc_type, mp_uint_t label) {
 }
 
 void asm_x64_entry(asm_x64_t *as, int num_locals) {
+    assert(num_locals >= 0);
     asm_x64_push_r64(as, ASM_X64_REG_RBP);
     asm_x64_mov_r64_r64(as, ASM_X64_REG_RBP, ASM_X64_REG_RSP);
-    if (num_locals < 0) {
-        num_locals = 0;
-    }
     num_locals |= 1; // make it odd so stack is aligned on 16 byte boundary
     asm_x64_sub_r64_i32(as, ASM_X64_REG_RSP, num_locals * WORD_SIZE);
     asm_x64_push_r64(as, ASM_X64_REG_RBX);
diff --git a/py/asmx64.h b/py/asmx64.h
index bf8bbd162..9ed2a6cf9 100644
--- a/py/asmx64.h
+++ b/py/asmx64.h
@@ -162,17 +162,12 @@ void asm_x64_call_ind(asm_x64_t* as, void* ptr, int temp_r32);
     } while (0)
 #define ASM_CALL_IND(as, ptr, idx) asm_x64_call_ind(as, ptr, ASM_X64_REG_RAX)
 
-#define ASM_MOV_REG_TO_LOCAL        asm_x64_mov_r64_to_local
-#define ASM_MOV_IMM_TO_REG          asm_x64_mov_i64_to_r64_optimised
-#define ASM_MOV_ALIGNED_IMM_TO_REG  asm_x64_mov_i64_to_r64_aligned
-#define ASM_MOV_IMM_TO_LOCAL_USING(as, imm, local_num, reg_temp) \
-    do { \
-        asm_x64_mov_i64_to_r64_optimised(as, (imm), (reg_temp)); \
-        asm_x64_mov_r64_to_local(as, (reg_temp), (local_num)); \
-    } while (false)
-#define ASM_MOV_LOCAL_TO_REG        asm_x64_mov_local_to_r64
+#define ASM_MOV_LOCAL_REG(as, local_num, reg_src) asm_x64_mov_r64_to_local((as), (reg_src), (local_num))
+#define ASM_MOV_REG_IMM(as, reg_dest, imm) asm_x64_mov_i64_to_r64_optimised((as), (imm), (reg_dest))
+#define ASM_MOV_REG_ALIGNED_IMM(as, reg_dest, imm) asm_x64_mov_i64_to_r64_aligned((as), (imm), (reg_dest))
+#define ASM_MOV_REG_LOCAL(as, reg_dest, local_num) asm_x64_mov_local_to_r64((as), (local_num), (reg_dest))
 #define ASM_MOV_REG_REG(as, reg_dest, reg_src) asm_x64_mov_r64_r64((as), (reg_dest), (reg_src))
-#define ASM_MOV_LOCAL_ADDR_TO_REG   asm_x64_mov_local_addr_to_r64
+#define ASM_MOV_REG_LOCAL_ADDR(as, reg_dest, local_num) asm_x64_mov_local_addr_to_r64((as), (local_num), (reg_dest))
 
 #define ASM_LSL_REG(as, reg) asm_x64_shl_r64_cl((as), (reg))
 #define ASM_ASR_REG(as, reg) asm_x64_sar_r64_cl((as), (reg))
diff --git a/py/asmx86.c b/py/asmx86.c
index 6a78fbd5e..3938baaac 100644
--- a/py/asmx86.c
+++ b/py/asmx86.c
@@ -387,7 +387,8 @@ void asm_x86_jcc_label(asm_x86_t *as, mp_uint_t jcc_type, mp_uint_t label) {
     }
 }
 
-void asm_x86_entry(asm_x86_t *as, mp_uint_t num_locals) {
+void asm_x86_entry(asm_x86_t *as, int num_locals) {
+    assert(num_locals >= 0);
     asm_x86_push_r32(as, ASM_X86_REG_EBP);
     asm_x86_mov_r32_r32(as, ASM_X86_REG_EBP, ASM_X86_REG_ESP);
     if (num_locals > 0) {
diff --git a/py/asmx86.h b/py/asmx86.h
index a5902987c..eb6c03eac 100644
--- a/py/asmx86.h
+++ b/py/asmx86.h
@@ -104,7 +104,7 @@ void asm_x86_test_r8_with_r8(asm_x86_t* as, int src_r32_a, int src_r32_b);
 void asm_x86_setcc_r8(asm_x86_t* as, mp_uint_t jcc_type, int dest_r8);
 void asm_x86_jmp_label(asm_x86_t* as, mp_uint_t label);
 void asm_x86_jcc_label(asm_x86_t* as, mp_uint_t jcc_type, mp_uint_t label);
-void asm_x86_entry(asm_x86_t* as, mp_uint_t num_locals);
+void asm_x86_entry(asm_x86_t* as, int num_locals);
 void asm_x86_exit(asm_x86_t* as);
 void asm_x86_mov_arg_to_r32(asm_x86_t *as, int src_arg_num, int dest_r32);
 void asm_x86_mov_local_to_r32(asm_x86_t* as, int src_local_num, int dest_r32);
@@ -160,17 +160,12 @@ void asm_x86_call_ind(asm_x86_t* as, void* ptr, mp_uint_t n_args, int temp_r32);
     } while (0)
 #define ASM_CALL_IND(as, ptr, idx) asm_x86_call_ind(as, ptr, mp_f_n_args[idx], ASM_X86_REG_EAX)
 
-#define ASM_MOV_REG_TO_LOCAL        asm_x86_mov_r32_to_local
-#define ASM_MOV_IMM_TO_REG          asm_x86_mov_i32_to_r32
-#define ASM_MOV_ALIGNED_IMM_TO_REG  asm_x86_mov_i32_to_r32_aligned
-#define ASM_MOV_IMM_TO_LOCAL_USING(as, imm, local_num, reg_temp) \
-    do { \
-        asm_x86_mov_i32_to_r32(as, (imm), (reg_temp)); \
-        asm_x86_mov_r32_to_local(as, (reg_temp), (local_num)); \
-    } while (false)
-#define ASM_MOV_LOCAL_TO_REG        asm_x86_mov_local_to_r32
+#define ASM_MOV_LOCAL_REG(as, local_num, reg_src) asm_x86_mov_r32_to_local((as), (reg_src), (local_num))
+#define ASM_MOV_REG_IMM(as, reg_dest, imm) asm_x86_mov_i32_to_r32((as), (imm), (reg_dest))
+#define ASM_MOV_REG_ALIGNED_IMM(as, reg_dest, imm) asm_x86_mov_i32_to_r32_aligned((as), (imm), (reg_dest))
+#define ASM_MOV_REG_LOCAL(as, reg_dest, local_num) asm_x86_mov_local_to_r32((as), (local_num), (reg_dest))
 #define ASM_MOV_REG_REG(as, reg_dest, reg_src) asm_x86_mov_r32_r32((as), (reg_dest), (reg_src))
-#define ASM_MOV_LOCAL_ADDR_TO_REG   asm_x86_mov_local_addr_to_r32
+#define ASM_MOV_REG_LOCAL_ADDR(as, reg_dest, local_num) asm_x86_mov_local_addr_to_r32((as), (local_num), (reg_dest))
 
 #define ASM_LSL_REG(as, reg) asm_x86_shl_r32_cl((as), (reg))
 #define ASM_ASR_REG(as, reg) asm_x86_sar_r32_cl((as), (reg))
diff --git a/py/asmxtensa.h b/py/asmxtensa.h
index 69de24b81..13d3e8234 100644
--- a/py/asmxtensa.h
+++ b/py/asmxtensa.h
@@ -280,17 +280,12 @@ void asm_xtensa_mov_reg_local_addr(asm_xtensa_t *as, uint reg_dest, int local_nu
         asm_xtensa_op_callx0(as, ASM_XTENSA_REG_A0); \
     } while (0)
 
-#define ASM_MOV_REG_TO_LOCAL(as, reg, local_num) asm_xtensa_mov_local_reg(as, (local_num), (reg))
-#define ASM_MOV_IMM_TO_REG(as, imm, reg) asm_xtensa_mov_reg_i32(as, (reg), (imm))
-#define ASM_MOV_ALIGNED_IMM_TO_REG(as, imm, reg) asm_xtensa_mov_reg_i32(as, (reg), (imm))
-#define ASM_MOV_IMM_TO_LOCAL_USING(as, imm, local_num, reg_temp) \
-    do { \
-        asm_xtensa_mov_reg_i32(as, (reg_temp), (imm)); \
-        asm_xtensa_mov_local_reg(as, (local_num), (reg_temp)); \
-    } while (0)
-#define ASM_MOV_LOCAL_TO_REG(as, local_num, reg) asm_xtensa_mov_reg_local(as, (reg), (local_num))
+#define ASM_MOV_LOCAL_REG(as, local_num, reg_src) asm_xtensa_mov_local_reg((as), (local_num), (reg_src))
+#define ASM_MOV_REG_IMM(as, reg_dest, imm) asm_xtensa_mov_reg_i32((as), (reg_dest), (imm))
+#define ASM_MOV_REG_ALIGNED_IMM(as, reg_dest, imm) asm_xtensa_mov_reg_i32((as), (reg_dest), (imm))
+#define ASM_MOV_REG_LOCAL(as, reg_dest, local_num) asm_xtensa_mov_reg_local((as), (reg_dest), (local_num))
 #define ASM_MOV_REG_REG(as, reg_dest, reg_src) asm_xtensa_op_mov_n((as), (reg_dest), (reg_src))
-#define ASM_MOV_LOCAL_ADDR_TO_REG(as, local_num, reg) asm_xtensa_mov_reg_local_addr(as, (reg), (local_num))
+#define ASM_MOV_REG_LOCAL_ADDR(as, reg_dest, local_num) asm_xtensa_mov_reg_local_addr((as), (reg_dest), (local_num))
 
 #define ASM_LSL_REG_REG(as, reg_dest, reg_shift) \
     do { \
diff --git a/py/builtinhelp.c b/py/builtinhelp.c
index 1cea8caac..4cea7e6d5 100644
--- a/py/builtinhelp.c
+++ b/py/builtinhelp.c
@@ -70,7 +70,7 @@ STATIC void mp_help_add_from_names(mp_obj_t list, const char *name) {
     while (*name) {
         size_t l = strlen(name);
         // name should end in '.py' and we strip it off
-        mp_obj_list_append(list, mp_obj_new_str(name, l - 3, false));
+        mp_obj_list_append(list, mp_obj_new_str(name, l - 3));
         name += l + 1;
     }
 }
@@ -109,7 +109,7 @@ STATIC void mp_help_print_modules(void) {
     // print the list of modules in a column-first order
     #define NUM_COLUMNS (4)
     #define COLUMN_WIDTH (18)
-    mp_uint_t len;
+    size_t len;
     mp_obj_t *items;
     mp_obj_list_get(list, &len, &items);
     unsigned int num_rows = (len + NUM_COLUMNS - 1) / NUM_COLUMNS;
diff --git a/py/builtinimport.c b/py/builtinimport.c
index c1437da4c..649cd11ef 100755
--- a/py/builtinimport.c
+++ b/py/builtinimport.c
@@ -46,6 +46,8 @@
 #define DEBUG_printf(...) (void)0
 #endif
 
+#if MICROPY_ENABLE_EXTERNAL_IMPORT
+
 #define PATH_SEP_CHAR '/'
 
 bool mp_obj_is_package(mp_obj_t module) {
@@ -335,7 +337,7 @@ mp_obj_t mp_builtin___import__(size_t n_args, const mp_obj_t *args) {
         }
 
         uint new_mod_l = (mod_len == 0 ? (size_t)(p - this_name) : (size_t)(p - this_name) + 1 + mod_len);
-        char *new_mod = alloca(new_mod_l);
+        char *new_mod = mp_local_alloc(new_mod_l);
         memcpy(new_mod, this_name, p - this_name);
         if (mod_len != 0) {
             new_mod[p - this_name] = '.';
@@ -343,9 +345,10 @@ mp_obj_t mp_builtin___import__(size_t n_args, const mp_obj_t *args) {
         }
 
         qstr new_mod_q = qstr_from_strn(new_mod, new_mod_l);
+        mp_local_free(new_mod);
         DEBUG_printf("Resolved base name for relative import: '%s'\n", qstr_str(new_mod_q));
         module_name = MP_OBJ_NEW_QSTR(new_mod_q);
-        mod_str = new_mod;
+        mod_str = qstr_str(new_mod_q);
         mod_len = new_mod_l;
     }
 
@@ -406,6 +409,7 @@ mp_obj_t mp_builtin___import__(size_t n_args, const mp_obj_t *args) {
                     }
                     // found weak linked module
                     module_obj = el->value;
+                    mp_module_call_init(mod_name, module_obj);
                 } else {
                     no_exist:
                 #else
@@ -452,7 +456,7 @@ mp_obj_t mp_builtin___import__(size_t n_args, const mp_obj_t *args) {
                     DEBUG_printf("%.*s is dir\n", vstr_len(&path), vstr_str(&path));
                     // https://docs.python.org/3/reference/import.html
                     // "Specifically, any module that contains a __path__ attribute is considered a package."
-                    mp_store_attr(module_obj, MP_QSTR___path__, mp_obj_new_str(vstr_str(&path), vstr_len(&path), false));
+                    mp_store_attr(module_obj, MP_QSTR___path__, mp_obj_new_str(vstr_str(&path), vstr_len(&path)));
                     size_t orig_path_len = path.len;
                     vstr_add_char(&path, PATH_SEP_CHAR);
                     vstr_add_str(&path, "__init__.py");
@@ -497,4 +501,41 @@ mp_obj_t mp_builtin___import__(size_t n_args, const mp_obj_t *args) {
     // Otherwise, we need to return top-level package
     return top_module_obj;
 }
+
+#else // MICROPY_ENABLE_EXTERNAL_IMPORT
+
+mp_obj_t mp_builtin___import__(size_t n_args, const mp_obj_t *args) {
+    // Check that it's not a relative import
+    if (n_args >= 5 && MP_OBJ_SMALL_INT_VALUE(args[4]) != 0) {
+        mp_raise_NotImplementedError("relative import");
+    }
+
+    // Check if module already exists, and return it if it does
+    qstr module_name_qstr = mp_obj_str_get_qstr(args[0]);
+    mp_obj_t module_obj = mp_module_get(module_name_qstr);
+    if (module_obj != MP_OBJ_NULL) {
+        return module_obj;
+    }
+
+    #if MICROPY_MODULE_WEAK_LINKS
+    // Check if there is a weak link to this module
+    mp_map_elem_t *el = mp_map_lookup((mp_map_t*)&mp_builtin_module_weak_links_map, MP_OBJ_NEW_QSTR(module_name_qstr), MP_MAP_LOOKUP);
+    if (el != NULL) {
+        // Found weak-linked module
+        mp_module_call_init(module_name_qstr, el->value);
+        return el->value;
+    }
+    #endif
+
+    // Couldn't find the module, so fail
+    if (MICROPY_ERROR_REPORTING == MICROPY_ERROR_REPORTING_TERSE) {
+        mp_raise_msg(&mp_type_ImportError, "module not found");
+    } else {
+        nlr_raise(mp_obj_new_exception_msg_varg(&mp_type_ImportError,
+            "no module named '%q'", module_name_qstr));
+    }
+}
+
+#endif // MICROPY_ENABLE_EXTERNAL_IMPORT
+
 MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mp_builtin___import___obj, 1, 5, mp_builtin___import__);
diff --git a/py/compile.c b/py/compile.c
index 4e704abfb..7daf91103 100644
--- a/py/compile.c
+++ b/py/compile.c
@@ -65,16 +65,16 @@ typedef enum {
 // we need a method table to do the lookup for the emitter functions
 #define EMIT(fun) (comp->emit_method_table->fun(comp->emit))
 #define EMIT_ARG(fun, ...) (comp->emit_method_table->fun(comp->emit, __VA_ARGS__))
-#define EMIT_LOAD_FAST(qst, local_num) (comp->emit_method_table->load_id.fast(comp->emit, qst, local_num))
-#define EMIT_LOAD_GLOBAL(qst) (comp->emit_method_table->load_id.global(comp->emit, qst))
+#define EMIT_LOAD_FAST(qst, local_num) (comp->emit_method_table->load_id.local(comp->emit, qst, local_num, MP_EMIT_IDOP_LOCAL_FAST))
+#define EMIT_LOAD_GLOBAL(qst) (comp->emit_method_table->load_id.global(comp->emit, qst, MP_EMIT_IDOP_GLOBAL_GLOBAL))
 
 #else
 
 // if we only have the bytecode emitter enabled then we can do a direct call to the functions
 #define EMIT(fun) (mp_emit_bc_##fun(comp->emit))
 #define EMIT_ARG(fun, ...) (mp_emit_bc_##fun(comp->emit, __VA_ARGS__))
-#define EMIT_LOAD_FAST(qst, local_num) (mp_emit_bc_load_fast(comp->emit, qst, local_num))
-#define EMIT_LOAD_GLOBAL(qst) (mp_emit_bc_load_global(comp->emit, qst))
+#define EMIT_LOAD_FAST(qst, local_num) (mp_emit_bc_load_local(comp->emit, qst, local_num, MP_EMIT_IDOP_LOCAL_FAST))
+#define EMIT_LOAD_GLOBAL(qst) (mp_emit_bc_load_global(comp->emit, qst, MP_EMIT_IDOP_GLOBAL_GLOBAL))
 
 #endif
 
@@ -273,7 +273,7 @@ STATIC void c_tuple(compiler_t *comp, mp_parse_node_t pn, mp_parse_node_struct_t
         }
         total += n;
     }
-    EMIT_ARG(build_tuple, total);
+    EMIT_ARG(build, total, MP_EMIT_BUILD_TUPLE);
 }
 
 STATIC void compile_generic_tuple(compiler_t *comp, mp_parse_node_struct_t *pns) {
@@ -366,37 +366,32 @@ STATIC void c_assign_atom_expr(compiler_t *comp, mp_parse_node_struct_t *pns, as
         if (MP_PARSE_NODE_STRUCT_KIND(pns1) == PN_trailer_bracket) {
             if (assign_kind == ASSIGN_AUG_STORE) {
                 EMIT(rot_three);
-                EMIT(store_subscr);
+                EMIT_ARG(subscr, MP_EMIT_SUBSCR_STORE);
             } else {
                 compile_node(comp, pns1->nodes[0]);
                 if (assign_kind == ASSIGN_AUG_LOAD) {
                     EMIT(dup_top_two);
-                    EMIT(load_subscr);
+                    EMIT_ARG(subscr, MP_EMIT_SUBSCR_LOAD);
                 } else {
-                    EMIT(store_subscr);
+                    EMIT_ARG(subscr, MP_EMIT_SUBSCR_STORE);
                 }
             }
+            return;
         } else if (MP_PARSE_NODE_STRUCT_KIND(pns1) == PN_trailer_period) {
             assert(MP_PARSE_NODE_IS_ID(pns1->nodes[0]));
             if (assign_kind == ASSIGN_AUG_LOAD) {
                 EMIT(dup_top);
-                EMIT_ARG(load_attr, MP_PARSE_NODE_LEAF_ARG(pns1->nodes[0]));
+                EMIT_ARG(attr, MP_PARSE_NODE_LEAF_ARG(pns1->nodes[0]), MP_EMIT_ATTR_LOAD);
             } else {
                 if (assign_kind == ASSIGN_AUG_STORE) {
                     EMIT(rot_two);
                 }
-                EMIT_ARG(store_attr, MP_PARSE_NODE_LEAF_ARG(pns1->nodes[0]));
+                EMIT_ARG(attr, MP_PARSE_NODE_LEAF_ARG(pns1->nodes[0]), MP_EMIT_ATTR_STORE);
             }
-        } else {
-            goto cannot_assign;
+            return;
         }
-    } else {
-        goto cannot_assign;
     }
 
-    return;
-
-cannot_assign:
     compile_syntax_error(comp, (mp_parse_node_t)pns, "can't assign to expression");
 }
 
@@ -657,12 +652,12 @@ STATIC void compile_funcdef_lambdef_param(compiler_t *comp, mp_parse_node_t pn)
                     // in MicroPython we put the default positional parameters into a tuple using the bytecode
                     // we need to do this here before we start building the map for the default keywords
                     if (comp->num_default_params > 0) {
-                        EMIT_ARG(build_tuple, comp->num_default_params);
+                        EMIT_ARG(build, comp->num_default_params, MP_EMIT_BUILD_TUPLE);
                     } else {
                         EMIT(load_null); // sentinel indicating empty default positional args
                     }
                     // first default dict param, so make the map
-                    EMIT_ARG(build_map, 0);
+                    EMIT_ARG(build, 0, MP_EMIT_BUILD_MAP);
                 }
 
                 // compile value then key, then store it to the dict
@@ -698,7 +693,7 @@ STATIC void compile_funcdef_lambdef(compiler_t *comp, scope_t *scope, mp_parse_n
     // in MicroPython we put the default positional parameters into a tuple using the bytecode
     // the default keywords args may have already made the tuple; if not, do it now
     if (comp->num_default_params > 0 && comp->num_dict_params == 0) {
-        EMIT_ARG(build_tuple, comp->num_default_params);
+        EMIT_ARG(build, comp->num_default_params, MP_EMIT_BUILD_TUPLE);
         EMIT(load_null); // sentinel indicating empty default keyword args
     }
 
@@ -825,7 +820,7 @@ STATIC void compile_decorated(compiler_t *comp, mp_parse_node_struct_t *pns) {
             compile_node(comp, name_nodes[0]);
             for (int j = 1; j < name_len; j++) {
                 assert(MP_PARSE_NODE_IS_ID(name_nodes[j])); // should be
-                EMIT_ARG(load_attr, MP_PARSE_NODE_LEAF_ARG(name_nodes[j]));
+                EMIT_ARG(attr, MP_PARSE_NODE_LEAF_ARG(name_nodes[j]), MP_EMIT_ATTR_LOAD);
             }
 
             // nodes[1] contains arguments to the decorator function, if any
@@ -889,10 +884,10 @@ STATIC void c_del_stmt(compiler_t *comp, mp_parse_node_t pn) {
             }
             if (MP_PARSE_NODE_STRUCT_KIND(pns1) == PN_trailer_bracket) {
                 compile_node(comp, pns1->nodes[0]);
-                EMIT(delete_subscr);
+                EMIT_ARG(subscr, MP_EMIT_SUBSCR_DELETE);
             } else if (MP_PARSE_NODE_STRUCT_KIND(pns1) == PN_trailer_period) {
                 assert(MP_PARSE_NODE_IS_ID(pns1->nodes[0]));
-                EMIT_ARG(delete_attr, MP_PARSE_NODE_LEAF_ARG(pns1->nodes[0]));
+                EMIT_ARG(attr, MP_PARSE_NODE_LEAF_ARG(pns1->nodes[0]), MP_EMIT_ATTR_DELETE);
             } else {
                 goto cannot_delete;
             }
@@ -950,20 +945,21 @@ STATIC void compile_del_stmt(compiler_t *comp, mp_parse_node_struct_t *pns) {
     apply_to_single_or_list(comp, pns->nodes[0], PN_exprlist, c_del_stmt);
 }
 
-STATIC void compile_break_stmt(compiler_t *comp, mp_parse_node_struct_t *pns) {
-    if (comp->break_label == INVALID_LABEL) {
-        compile_syntax_error(comp, (mp_parse_node_t)pns, "'break' outside loop");
+STATIC void compile_break_cont_stmt(compiler_t *comp, mp_parse_node_struct_t *pns) {
+    uint16_t label;
+    const char *error_msg;
+    if (MP_PARSE_NODE_STRUCT_KIND(pns) == PN_break_stmt) {
+        label = comp->break_label;
+        error_msg = "'break' outside loop";
+    } else {
+        label = comp->continue_label;
+        error_msg = "'continue' outside loop";
     }
-    assert(comp->cur_except_level >= comp->break_continue_except_level);
-    EMIT_ARG(break_loop, comp->break_label, comp->cur_except_level - comp->break_continue_except_level);
-}
-
-STATIC void compile_continue_stmt(compiler_t *comp, mp_parse_node_struct_t *pns) {
-    if (comp->continue_label == INVALID_LABEL) {
-        compile_syntax_error(comp, (mp_parse_node_t)pns, "'continue' outside loop");
+    if (label == INVALID_LABEL) {
+        compile_syntax_error(comp, (mp_parse_node_t)pns, error_msg);
     }
     assert(comp->cur_except_level >= comp->break_continue_except_level);
-    EMIT_ARG(continue_loop, comp->continue_label, comp->cur_except_level - comp->break_continue_except_level);
+    EMIT_ARG(unwind_jump, label, comp->cur_except_level - comp->break_continue_except_level);
 }
 
 STATIC void compile_return_stmt(compiler_t *comp, mp_parse_node_struct_t *pns) {
@@ -1029,14 +1025,14 @@ STATIC void do_import_name(compiler_t *comp, mp_parse_node_t pn, qstr *q_base) {
     if (MP_PARSE_NODE_IS_NULL(pn)) {
         // empty name (eg, from . import x)
         *q_base = MP_QSTR_;
-        EMIT_ARG(import_name, MP_QSTR_); // import the empty string
+        EMIT_ARG(import, MP_QSTR_, MP_EMIT_IMPORT_NAME); // import the empty string
     } else if (MP_PARSE_NODE_IS_ID(pn)) {
         // just a simple name
         qstr q_full = MP_PARSE_NODE_LEAF_ARG(pn);
         if (!is_as) {
             *q_base = q_full;
         }
-        EMIT_ARG(import_name, q_full);
+        EMIT_ARG(import, q_full, MP_EMIT_IMPORT_NAME);
     } else {
         assert(MP_PARSE_NODE_IS_STRUCT_KIND(pn, PN_dotted_name)); // should be
         mp_parse_node_struct_t *pns = (mp_parse_node_struct_t*)pn;
@@ -1050,8 +1046,8 @@ STATIC void do_import_name(compiler_t *comp, mp_parse_node_t pn, qstr *q_base) {
             for (int i = 0; i < n; i++) {
                 len += qstr_len(MP_PARSE_NODE_LEAF_ARG(pns->nodes[i]));
             }
-            byte *q_ptr;
-            byte *str_dest = qstr_build_start(len, &q_ptr);
+            char *q_ptr = mp_local_alloc(len);
+            char *str_dest = q_ptr;
             for (int i = 0; i < n; i++) {
                 if (i > 0) {
                     *str_dest++ = '.';
@@ -1061,11 +1057,12 @@ STATIC void do_import_name(compiler_t *comp, mp_parse_node_t pn, qstr *q_base) {
                 memcpy(str_dest, str_src, str_src_len);
                 str_dest += str_src_len;
             }
-            qstr q_full = qstr_build_end(q_ptr);
-            EMIT_ARG(import_name, q_full);
+            qstr q_full = qstr_from_strn(q_ptr, len);
+            mp_local_free(q_ptr);
+            EMIT_ARG(import, q_full, MP_EMIT_IMPORT_NAME);
             if (is_as) {
                 for (int i = 1; i < n; i++) {
-                    EMIT_ARG(load_attr, MP_PARSE_NODE_LEAF_ARG(pns->nodes[i]));
+                    EMIT_ARG(attr, MP_PARSE_NODE_LEAF_ARG(pns->nodes[i]), MP_EMIT_ATTR_LOAD);
                 }
             }
         }
@@ -1126,12 +1123,12 @@ STATIC void compile_import_from(compiler_t *comp, mp_parse_node_struct_t *pns) {
 
         // build the "fromlist" tuple
         EMIT_ARG(load_const_str, MP_QSTR__star_);
-        EMIT_ARG(build_tuple, 1);
+        EMIT_ARG(build, 1, MP_EMIT_BUILD_TUPLE);
 
         // do the import
         qstr dummy_q;
         do_import_name(comp, pn_import_source, &dummy_q);
-        EMIT(import_star);
+        EMIT_ARG(import, MP_QSTR_NULL, MP_EMIT_IMPORT_STAR);
 
     } else {
         EMIT_ARG(load_const_small_int, import_level);
@@ -1145,7 +1142,7 @@ STATIC void compile_import_from(compiler_t *comp, mp_parse_node_struct_t *pns) {
             qstr id2 = MP_PARSE_NODE_LEAF_ARG(pns3->nodes[0]); // should be id
             EMIT_ARG(load_const_str, id2);
         }
-        EMIT_ARG(build_tuple, n);
+        EMIT_ARG(build, n, MP_EMIT_BUILD_TUPLE);
 
         // do the import
         qstr dummy_q;
@@ -1154,7 +1151,7 @@ STATIC void compile_import_from(compiler_t *comp, mp_parse_node_struct_t *pns) {
             assert(MP_PARSE_NODE_IS_STRUCT_KIND(pn_nodes[i], PN_import_as_name));
             mp_parse_node_struct_t *pns3 = (mp_parse_node_struct_t*)pn_nodes[i];
             qstr id2 = MP_PARSE_NODE_LEAF_ARG(pns3->nodes[0]); // should be id
-            EMIT_ARG(import_from, id2);
+            EMIT_ARG(import, id2, MP_EMIT_IMPORT_FROM);
             if (MP_PARSE_NODE_IS_NULL(pns3->nodes[1])) {
                 compile_store_id(comp, id2);
             } else {
@@ -1165,9 +1162,7 @@ STATIC void compile_import_from(compiler_t *comp, mp_parse_node_struct_t *pns) {
     }
 }
 
-STATIC void compile_declare_global(compiler_t *comp, mp_parse_node_t pn, qstr qst) {
-    bool added;
-    id_info_t *id_info = scope_find_or_add_id(comp->scope_cur, qst, &added);
+STATIC void compile_declare_global(compiler_t *comp, mp_parse_node_t pn, qstr qst, bool added, id_info_t *id_info) {
     if (!added && id_info->kind != ID_INFO_KIND_GLOBAL_EXPLICIT) {
         compile_syntax_error(comp, pn, "identifier redefined as global");
         return;
@@ -1181,19 +1176,7 @@ STATIC void compile_declare_global(compiler_t *comp, mp_parse_node_t pn, qstr qs
     }
 }
 
-STATIC void compile_global_stmt(compiler_t *comp, mp_parse_node_struct_t *pns) {
-    if (comp->pass == MP_PASS_SCOPE) {
-        mp_parse_node_t *nodes;
-        int n = mp_parse_node_extract_list(&pns->nodes[0], PN_name_list, &nodes);
-        for (int i = 0; i < n; i++) {
-            compile_declare_global(comp, (mp_parse_node_t)pns, MP_PARSE_NODE_LEAF_ARG(nodes[i]));
-        }
-    }
-}
-
-STATIC void compile_declare_nonlocal(compiler_t *comp, mp_parse_node_t pn, qstr qst) {
-    bool added;
-    id_info_t *id_info = scope_find_or_add_id(comp->scope_cur, qst, &added);
+STATIC void compile_declare_nonlocal(compiler_t *comp, mp_parse_node_t pn, qstr qst, bool added, id_info_t *id_info) {
     if (added) {
         scope_find_local_and_close_over(comp->scope_cur, id_info, qst);
         if (id_info->kind == ID_INFO_KIND_GLOBAL_IMPLICIT) {
@@ -1204,16 +1187,26 @@ STATIC void compile_declare_nonlocal(compiler_t *comp, mp_parse_node_t pn, qstr
     }
 }
 
-STATIC void compile_nonlocal_stmt(compiler_t *comp, mp_parse_node_struct_t *pns) {
+STATIC void compile_global_nonlocal_stmt(compiler_t *comp, mp_parse_node_struct_t *pns) {
     if (comp->pass == MP_PASS_SCOPE) {
-        if (comp->scope_cur->kind == SCOPE_MODULE) {
+        bool is_global = MP_PARSE_NODE_STRUCT_KIND(pns) == PN_global_stmt;
+
+        if (!is_global && comp->scope_cur->kind == SCOPE_MODULE) {
             compile_syntax_error(comp, (mp_parse_node_t)pns, "can't declare nonlocal in outer code");
             return;
         }
+
         mp_parse_node_t *nodes;
         int n = mp_parse_node_extract_list(&pns->nodes[0], PN_name_list, &nodes);
         for (int i = 0; i < n; i++) {
-            compile_declare_nonlocal(comp, (mp_parse_node_t)pns, MP_PARSE_NODE_LEAF_ARG(nodes[i]));
+            qstr qst = MP_PARSE_NODE_LEAF_ARG(nodes[i]);
+            bool added;
+            id_info_t *id_info = scope_find_or_add_id(comp->scope_cur, qst, &added);
+            if (is_global) {
+                compile_declare_global(comp, (mp_parse_node_t)pns, qst, added, id_info);
+            } else {
+                compile_declare_nonlocal(comp, (mp_parse_node_t)pns, qst, added, id_info);
+            }
         }
     }
 }
@@ -1520,7 +1513,7 @@ STATIC void compile_try_except(compiler_t *comp, mp_parse_node_t pn_body, int n_
     uint l1 = comp_next_label(comp);
     uint success_label = comp_next_label(comp);
 
-    EMIT_ARG(setup_except, l1);
+    EMIT_ARG(setup_block, l1, MP_EMIT_SETUP_BLOCK_EXCEPT);
     compile_increase_except_level(comp);
 
     compile_node(comp, pn_body); // body
@@ -1575,7 +1568,7 @@ STATIC void compile_try_except(compiler_t *comp, mp_parse_node_t pn_body, int n_
         uint l3 = 0;
         if (qstr_exception_local != 0) {
             l3 = comp_next_label(comp);
-            EMIT_ARG(setup_finally, l3);
+            EMIT_ARG(setup_block, l3, MP_EMIT_SETUP_BLOCK_FINALLY);
             compile_increase_except_level(comp);
         }
         compile_node(comp, pns_except->nodes[1]);
@@ -1610,7 +1603,7 @@ STATIC void compile_try_except(compiler_t *comp, mp_parse_node_t pn_body, int n_
 STATIC void compile_try_finally(compiler_t *comp, mp_parse_node_t pn_body, int n_except, mp_parse_node_t *pn_except, mp_parse_node_t pn_else, mp_parse_node_t pn_finally) {
     uint l_finally_block = comp_next_label(comp);
 
-    EMIT_ARG(setup_finally, l_finally_block);
+    EMIT_ARG(setup_block, l_finally_block, MP_EMIT_SETUP_BLOCK_FINALLY);
     compile_increase_except_level(comp);
 
     if (n_except == 0) {
@@ -1672,12 +1665,12 @@ STATIC void compile_with_stmt_helper(compiler_t *comp, int n, mp_parse_node_t *n
             // this pre-bit is of the form "a as b"
             mp_parse_node_struct_t *pns = (mp_parse_node_struct_t*)nodes[0];
             compile_node(comp, pns->nodes[0]);
-            EMIT_ARG(setup_with, l_end);
+            EMIT_ARG(setup_block, l_end, MP_EMIT_SETUP_BLOCK_WITH);
             c_assign(comp, pns->nodes[1], ASSIGN_STORE);
         } else {
             // this pre-bit is just an expression
             compile_node(comp, nodes[0]);
-            EMIT_ARG(setup_with, l_end);
+            EMIT_ARG(setup_block, l_end, MP_EMIT_SETUP_BLOCK_WITH);
             EMIT(pop_top);
         }
         compile_increase_except_level(comp);
@@ -1703,7 +1696,7 @@ STATIC void compile_with_stmt(compiler_t *comp, mp_parse_node_struct_t *pns) {
 STATIC void compile_yield_from(compiler_t *comp) {
     EMIT_ARG(get_iter, false);
     EMIT_ARG(load_const_tok, MP_TOKEN_KW_NONE);
-    EMIT(yield_from);
+    EMIT_ARG(yield, MP_EMIT_YIELD_FROM);
 }
 
 #if MICROPY_PY_ASYNC_AWAIT
@@ -1730,7 +1723,7 @@ STATIC void compile_async_for_stmt(compiler_t *comp, mp_parse_node_struct_t *pns
 
     EMIT_ARG(label_assign, continue_label);
 
-    EMIT_ARG(setup_except, try_exception_label);
+    EMIT_ARG(setup_block, try_exception_label, MP_EMIT_SETUP_BLOCK_EXCEPT);
     compile_increase_except_level(comp);
 
     compile_load_id(comp, context);
@@ -1801,7 +1794,7 @@ STATIC void compile_async_with_stmt_helper(compiler_t *comp, int n, mp_parse_nod
         compile_load_id(comp, context);
         EMIT_ARG(load_method, MP_QSTR___aexit__, false);
 
-        EMIT_ARG(setup_except, try_exception_label);
+        EMIT_ARG(setup_block, try_exception_label, MP_EMIT_SETUP_BLOCK_EXCEPT);
         compile_increase_except_level(comp);
         // compile additional pre-bits and the body
         compile_async_with_stmt_helper(comp, n - 1, nodes + 1, body);
@@ -1815,7 +1808,7 @@ STATIC void compile_async_with_stmt_helper(compiler_t *comp, int n, mp_parse_nod
         // at this point the stack contains: ..., __aexit__, self, exc
         EMIT(dup_top);
         #if MICROPY_CPYTHON_COMPAT
-        EMIT_ARG(load_attr, MP_QSTR___class__); // get type(exc)
+        EMIT_ARG(attr, MP_QSTR___class__, MP_EMIT_ATTR_LOAD); // get type(exc)
         #else
         compile_load_id(comp, MP_QSTR_type);
         EMIT(rot_two);
@@ -1940,66 +1933,58 @@ STATIC void compile_expr_stmt(compiler_t *comp, mp_parse_node_struct_t *pns) {
             }
         } else {
         plain_assign:
-            if (MICROPY_COMP_DOUBLE_TUPLE_ASSIGN
-                && MP_PARSE_NODE_IS_STRUCT_KIND(pns->nodes[1], PN_testlist_star_expr)
-                && MP_PARSE_NODE_IS_STRUCT_KIND(pns->nodes[0], PN_testlist_star_expr)
-                && MP_PARSE_NODE_STRUCT_NUM_NODES((mp_parse_node_struct_t*)pns->nodes[1]) == 2
-                && MP_PARSE_NODE_STRUCT_NUM_NODES((mp_parse_node_struct_t*)pns->nodes[0]) == 2) {
-                // optimisation for a, b = c, d
-                mp_parse_node_struct_t *pns10 = (mp_parse_node_struct_t*)pns->nodes[1];
-                mp_parse_node_struct_t *pns0 = (mp_parse_node_struct_t*)pns->nodes[0];
-                if (MP_PARSE_NODE_IS_STRUCT_KIND(pns0->nodes[0], PN_star_expr)
-                    || MP_PARSE_NODE_IS_STRUCT_KIND(pns0->nodes[1], PN_star_expr)) {
-                    // can't optimise when it's a star expression on the lhs
-                    goto no_optimisation;
-                }
-                compile_node(comp, pns10->nodes[0]); // rhs
-                compile_node(comp, pns10->nodes[1]); // rhs
-                EMIT(rot_two);
-                c_assign(comp, pns0->nodes[0], ASSIGN_STORE); // lhs store
-                c_assign(comp, pns0->nodes[1], ASSIGN_STORE); // lhs store
-            } else if (MICROPY_COMP_TRIPLE_TUPLE_ASSIGN
-                && MP_PARSE_NODE_IS_STRUCT_KIND(pns->nodes[1], PN_testlist_star_expr)
-                && MP_PARSE_NODE_IS_STRUCT_KIND(pns->nodes[0], PN_testlist_star_expr)
-                && MP_PARSE_NODE_STRUCT_NUM_NODES((mp_parse_node_struct_t*)pns->nodes[1]) == 3
-                && MP_PARSE_NODE_STRUCT_NUM_NODES((mp_parse_node_struct_t*)pns->nodes[0]) == 3) {
-                // optimisation for a, b, c = d, e, f
-                mp_parse_node_struct_t *pns10 = (mp_parse_node_struct_t*)pns->nodes[1];
+            #if MICROPY_COMP_DOUBLE_TUPLE_ASSIGN
+            if (MP_PARSE_NODE_IS_STRUCT_KIND(pns->nodes[1], PN_testlist_star_expr)
+                && MP_PARSE_NODE_IS_STRUCT_KIND(pns->nodes[0], PN_testlist_star_expr)) {
                 mp_parse_node_struct_t *pns0 = (mp_parse_node_struct_t*)pns->nodes[0];
-                if (MP_PARSE_NODE_IS_STRUCT_KIND(pns0->nodes[0], PN_star_expr)
-                    || MP_PARSE_NODE_IS_STRUCT_KIND(pns0->nodes[1], PN_star_expr)
-                    || MP_PARSE_NODE_IS_STRUCT_KIND(pns0->nodes[2], PN_star_expr)) {
-                    // can't optimise when it's a star expression on the lhs
-                    goto no_optimisation;
+                pns1 = (mp_parse_node_struct_t*)pns->nodes[1];
+                uint32_t n_pns0 = MP_PARSE_NODE_STRUCT_NUM_NODES(pns0);
+                // Can only optimise a tuple-to-tuple assignment when all of the following hold:
+                //  - equal number of items in LHS and RHS tuples
+                //  - 2 or 3 items in the tuples
+                //  - there are no star expressions in the LHS tuple
+                if (n_pns0 == MP_PARSE_NODE_STRUCT_NUM_NODES(pns1)
+                    && (n_pns0 == 2
+                        #if MICROPY_COMP_TRIPLE_TUPLE_ASSIGN
+                        || n_pns0 == 3
+                        #endif
+                        )
+                    && !MP_PARSE_NODE_IS_STRUCT_KIND(pns0->nodes[0], PN_star_expr)
+                    && !MP_PARSE_NODE_IS_STRUCT_KIND(pns0->nodes[1], PN_star_expr)
+                    #if MICROPY_COMP_TRIPLE_TUPLE_ASSIGN
+                    && (n_pns0 == 2 || !MP_PARSE_NODE_IS_STRUCT_KIND(pns0->nodes[2], PN_star_expr))
+                    #endif
+                    ) {
+                    // Optimisation for a, b = c, d or a, b, c = d, e, f
+                    compile_node(comp, pns1->nodes[0]); // rhs
+                    compile_node(comp, pns1->nodes[1]); // rhs
+                    #if MICROPY_COMP_TRIPLE_TUPLE_ASSIGN
+                    if (n_pns0 == 3) {
+                        compile_node(comp, pns1->nodes[2]); // rhs
+                        EMIT(rot_three);
+                    }
+                    #endif
+                    EMIT(rot_two);
+                    c_assign(comp, pns0->nodes[0], ASSIGN_STORE); // lhs store
+                    c_assign(comp, pns0->nodes[1], ASSIGN_STORE); // lhs store
+                    #if MICROPY_COMP_TRIPLE_TUPLE_ASSIGN
+                    if (n_pns0 == 3) {
+                        c_assign(comp, pns0->nodes[2], ASSIGN_STORE); // lhs store
+                    }
+                    #endif
+                    return;
                 }
-                compile_node(comp, pns10->nodes[0]); // rhs
-                compile_node(comp, pns10->nodes[1]); // rhs
-                compile_node(comp, pns10->nodes[2]); // rhs
-                EMIT(rot_three);
-                EMIT(rot_two);
-                c_assign(comp, pns0->nodes[0], ASSIGN_STORE); // lhs store
-                c_assign(comp, pns0->nodes[1], ASSIGN_STORE); // lhs store
-                c_assign(comp, pns0->nodes[2], ASSIGN_STORE); // lhs store
-            } else {
-                no_optimisation:
-                compile_node(comp, pns->nodes[1]); // rhs
-                c_assign(comp, pns->nodes[0], ASSIGN_STORE); // lhs store
             }
+            #endif
+
+            compile_node(comp, pns->nodes[1]); // rhs
+            c_assign(comp, pns->nodes[0], ASSIGN_STORE); // lhs store
         }
     } else {
         goto plain_assign;
     }
 }
 
-STATIC void c_binary_op(compiler_t *comp, mp_parse_node_struct_t *pns, mp_binary_op_t binary_op) {
-    int num_nodes = MP_PARSE_NODE_STRUCT_NUM_NODES(pns);
-    compile_node(comp, pns->nodes[0]);
-    for (int i = 1; i < num_nodes; i += 1) {
-        compile_node(comp, pns->nodes[i]);
-        EMIT_ARG(binary_op, binary_op);
-    }
-}
-
 STATIC void compile_test_if_expr(compiler_t *comp, mp_parse_node_struct_t *pns) {
     assert(MP_PARSE_NODE_IS_STRUCT_KIND(pns->nodes[1], PN_test_if_else));
     mp_parse_node_struct_t *pns_test_if_else = (mp_parse_node_struct_t*)pns->nodes[1];
@@ -2030,7 +2015,8 @@ STATIC void compile_lambdef(compiler_t *comp, mp_parse_node_struct_t *pns) {
     compile_funcdef_lambdef(comp, this_scope, pns->nodes[0], PN_varargslist);
 }
 
-STATIC void compile_or_and_test(compiler_t *comp, mp_parse_node_struct_t *pns, bool cond) {
+STATIC void compile_or_and_test(compiler_t *comp, mp_parse_node_struct_t *pns) {
+    bool cond = MP_PARSE_NODE_STRUCT_KIND(pns) == PN_or_test;
     uint l_end = comp_next_label(comp);
     int n = MP_PARSE_NODE_STRUCT_NUM_NODES(pns);
     for (int i = 0; i < n; i += 1) {
@@ -2042,14 +2028,6 @@ STATIC void compile_or_and_test(compiler_t *comp, mp_parse_node_struct_t *pns, b
     EMIT_ARG(label_assign, l_end);
 }
 
-STATIC void compile_or_test(compiler_t *comp, mp_parse_node_struct_t *pns) {
-    compile_or_and_test(comp, pns, true);
-}
-
-STATIC void compile_and_test(compiler_t *comp, mp_parse_node_struct_t *pns) {
-    compile_or_and_test(comp, pns, false);
-}
-
 STATIC void compile_not_test_2(compiler_t *comp, mp_parse_node_struct_t *pns) {
     compile_node(comp, pns->nodes[0]);
     EMIT_ARG(unary_op, MP_UNARY_OP_NOT);
@@ -2115,16 +2093,16 @@ STATIC void compile_star_expr(compiler_t *comp, mp_parse_node_struct_t *pns) {
     compile_syntax_error(comp, (mp_parse_node_t)pns, "*x must be assignment target");
 }
 
-STATIC void compile_expr(compiler_t *comp, mp_parse_node_struct_t *pns) {
-    c_binary_op(comp, pns, MP_BINARY_OP_OR);
-}
-
-STATIC void compile_xor_expr(compiler_t *comp, mp_parse_node_struct_t *pns) {
-    c_binary_op(comp, pns, MP_BINARY_OP_XOR);
-}
-
-STATIC void compile_and_expr(compiler_t *comp, mp_parse_node_struct_t *pns) {
-    c_binary_op(comp, pns, MP_BINARY_OP_AND);
+STATIC void compile_binary_op(compiler_t *comp, mp_parse_node_struct_t *pns) {
+    MP_STATIC_ASSERT(MP_BINARY_OP_OR + PN_xor_expr - PN_expr == MP_BINARY_OP_XOR);
+    MP_STATIC_ASSERT(MP_BINARY_OP_OR + PN_and_expr - PN_expr == MP_BINARY_OP_AND);
+    mp_binary_op_t binary_op = MP_BINARY_OP_OR + MP_PARSE_NODE_STRUCT_KIND(pns) - PN_expr;
+    int num_nodes = MP_PARSE_NODE_STRUCT_NUM_NODES(pns);
+    compile_node(comp, pns->nodes[0]);
+    for (int i = 1; i < num_nodes; ++i) {
+        compile_node(comp, pns->nodes[i]);
+        EMIT_ARG(binary_op, binary_op);
+    }
 }
 
 STATIC void compile_term(compiler_t *comp, mp_parse_node_struct_t *pns) {
@@ -2400,7 +2378,7 @@ STATIC void compile_atom_paren(compiler_t *comp, mp_parse_node_struct_t *pns) {
 STATIC void compile_atom_bracket(compiler_t *comp, mp_parse_node_struct_t *pns) {
     if (MP_PARSE_NODE_IS_NULL(pns->nodes[0])) {
         // empty list
-        EMIT_ARG(build_list, 0);
+        EMIT_ARG(build, 0, MP_EMIT_BUILD_LIST);
     } else if (MP_PARSE_NODE_IS_STRUCT_KIND(pns->nodes[0], PN_testlist_comp)) {
         mp_parse_node_struct_t *pns2 = (mp_parse_node_struct_t*)pns->nodes[0];
         if (MP_PARSE_NODE_IS_STRUCT(pns2->nodes[1])) {
@@ -2409,12 +2387,12 @@ STATIC void compile_atom_bracket(compiler_t *comp, mp_parse_node_struct_t *pns)
                 // list of one item, with trailing comma
                 assert(MP_PARSE_NODE_IS_NULL(pns3->nodes[0]));
                 compile_node(comp, pns2->nodes[0]);
-                EMIT_ARG(build_list, 1);
+                EMIT_ARG(build, 1, MP_EMIT_BUILD_LIST);
             } else if (MP_PARSE_NODE_STRUCT_KIND(pns3) == PN_testlist_comp_3c) {
                 // list of many items
                 compile_node(comp, pns2->nodes[0]);
                 compile_generic_all_nodes(comp, pns3);
-                EMIT_ARG(build_list, 1 + MP_PARSE_NODE_STRUCT_NUM_NODES(pns3));
+                EMIT_ARG(build, 1 + MP_PARSE_NODE_STRUCT_NUM_NODES(pns3), MP_EMIT_BUILD_LIST);
             } else if (MP_PARSE_NODE_STRUCT_KIND(pns3) == PN_comp_for) {
                 // list comprehension
                 compile_comprehension(comp, pns2, SCOPE_LIST_COMP);
@@ -2427,12 +2405,12 @@ STATIC void compile_atom_bracket(compiler_t *comp, mp_parse_node_struct_t *pns)
             list_with_2_items:
             compile_node(comp, pns2->nodes[0]);
             compile_node(comp, pns2->nodes[1]);
-            EMIT_ARG(build_list, 2);
+            EMIT_ARG(build, 2, MP_EMIT_BUILD_LIST);
         }
     } else {
         // list with 1 item
         compile_node(comp, pns->nodes[0]);
-        EMIT_ARG(build_list, 1);
+        EMIT_ARG(build, 1, MP_EMIT_BUILD_LIST);
     }
 }
 
@@ -2440,12 +2418,12 @@ STATIC void compile_atom_brace(compiler_t *comp, mp_parse_node_struct_t *pns) {
     mp_parse_node_t pn = pns->nodes[0];
     if (MP_PARSE_NODE_IS_NULL(pn)) {
         // empty dict
-        EMIT_ARG(build_map, 0);
+        EMIT_ARG(build, 0, MP_EMIT_BUILD_MAP);
     } else if (MP_PARSE_NODE_IS_STRUCT(pn)) {
         pns = (mp_parse_node_struct_t*)pn;
         if (MP_PARSE_NODE_STRUCT_KIND(pns) == PN_dictorsetmaker_item) {
             // dict with one element
-            EMIT_ARG(build_map, 1);
+            EMIT_ARG(build, 1, MP_EMIT_BUILD_MAP);
             compile_node(comp, pn);
             EMIT(store_map);
         } else if (MP_PARSE_NODE_STRUCT_KIND(pns) == PN_dictorsetmaker) {
@@ -2462,7 +2440,7 @@ STATIC void compile_atom_brace(compiler_t *comp, mp_parse_node_struct_t *pns) {
                 bool is_dict;
                 if (!MICROPY_PY_BUILTINS_SET || MP_PARSE_NODE_IS_STRUCT_KIND(pns->nodes[0], PN_dictorsetmaker_item)) {
                     // a dictionary
-                    EMIT_ARG(build_map, 1 + n);
+                    EMIT_ARG(build, 1 + n, MP_EMIT_BUILD_MAP);
                     compile_node(comp, pns->nodes[0]);
                     EMIT(store_map);
                     is_dict = true;
@@ -2502,7 +2480,7 @@ STATIC void compile_atom_brace(compiler_t *comp, mp_parse_node_struct_t *pns) {
                 #if MICROPY_PY_BUILTINS_SET
                 // if it's a set, build it
                 if (!is_dict) {
-                    EMIT_ARG(build_set, 1 + n);
+                    EMIT_ARG(build, 1 + n, MP_EMIT_BUILD_SET);
                 }
                 #endif
             } else {
@@ -2525,7 +2503,7 @@ STATIC void compile_atom_brace(compiler_t *comp, mp_parse_node_struct_t *pns) {
         set_with_one_element:
         #if MICROPY_PY_BUILTINS_SET
         compile_node(comp, pn);
-        EMIT_ARG(build_set, 1);
+        EMIT_ARG(build, 1, MP_EMIT_BUILD_SET);
         #else
         assert(0);
         #endif
@@ -2539,22 +2517,31 @@ STATIC void compile_trailer_paren(compiler_t *comp, mp_parse_node_struct_t *pns)
 STATIC void compile_trailer_bracket(compiler_t *comp, mp_parse_node_struct_t *pns) {
     // object who's index we want is on top of stack
     compile_node(comp, pns->nodes[0]); // the index
-    EMIT(load_subscr);
+    EMIT_ARG(subscr, MP_EMIT_SUBSCR_LOAD);
 }
 
 STATIC void compile_trailer_period(compiler_t *comp, mp_parse_node_struct_t *pns) {
     // object who's attribute we want is on top of stack
-    EMIT_ARG(load_attr, MP_PARSE_NODE_LEAF_ARG(pns->nodes[0])); // attribute to get
+    EMIT_ARG(attr, MP_PARSE_NODE_LEAF_ARG(pns->nodes[0]), MP_EMIT_ATTR_LOAD); // attribute to get
 }
 
 #if MICROPY_PY_BUILTINS_SLICE
-STATIC void compile_subscript_3_helper(compiler_t *comp, mp_parse_node_struct_t *pns) {
+STATIC void compile_subscript(compiler_t *comp, mp_parse_node_struct_t *pns) {
+    if (MP_PARSE_NODE_STRUCT_KIND(pns) == PN_subscript_2) {
+        compile_node(comp, pns->nodes[0]); // start of slice
+        assert(MP_PARSE_NODE_IS_STRUCT(pns->nodes[1])); // should always be
+        pns = (mp_parse_node_struct_t*)pns->nodes[1];
+    } else {
+        // pns is a PN_subscript_3, load None for start of slice
+        EMIT_ARG(load_const_tok, MP_TOKEN_KW_NONE);
+    }
+
     assert(MP_PARSE_NODE_STRUCT_KIND(pns) == PN_subscript_3); // should always be
     mp_parse_node_t pn = pns->nodes[0];
     if (MP_PARSE_NODE_IS_NULL(pn)) {
         // [?:]
         EMIT_ARG(load_const_tok, MP_TOKEN_KW_NONE);
-        EMIT_ARG(build_slice, 2);
+        EMIT_ARG(build, 2, MP_EMIT_BUILD_SLICE);
     } else if (MP_PARSE_NODE_IS_STRUCT(pn)) {
         pns = (mp_parse_node_struct_t*)pn;
         if (MP_PARSE_NODE_STRUCT_KIND(pns) == PN_subscript_3c) {
@@ -2562,11 +2549,11 @@ STATIC void compile_subscript_3_helper(compiler_t *comp, mp_parse_node_struct_t
             pn = pns->nodes[0];
             if (MP_PARSE_NODE_IS_NULL(pn)) {
                 // [?::]
-                EMIT_ARG(build_slice, 2);
+                EMIT_ARG(build, 2, MP_EMIT_BUILD_SLICE);
             } else {
                 // [?::x]
                 compile_node(comp, pn);
-                EMIT_ARG(build_slice, 3);
+                EMIT_ARG(build, 3, MP_EMIT_BUILD_SLICE);
             }
         } else if (MP_PARSE_NODE_STRUCT_KIND(pns) == PN_subscript_3d) {
             compile_node(comp, pns->nodes[0]);
@@ -2575,34 +2562,23 @@ STATIC void compile_subscript_3_helper(compiler_t *comp, mp_parse_node_struct_t
             assert(MP_PARSE_NODE_STRUCT_KIND(pns) == PN_sliceop); // should always be
             if (MP_PARSE_NODE_IS_NULL(pns->nodes[0])) {
                 // [?:x:]
-                EMIT_ARG(build_slice, 2);
+                EMIT_ARG(build, 2, MP_EMIT_BUILD_SLICE);
             } else {
                 // [?:x:x]
                 compile_node(comp, pns->nodes[0]);
-                EMIT_ARG(build_slice, 3);
+                EMIT_ARG(build, 3, MP_EMIT_BUILD_SLICE);
             }
         } else {
             // [?:x]
             compile_node(comp, pn);
-            EMIT_ARG(build_slice, 2);
+            EMIT_ARG(build, 2, MP_EMIT_BUILD_SLICE);
         }
     } else {
         // [?:x]
         compile_node(comp, pn);
-        EMIT_ARG(build_slice, 2);
+        EMIT_ARG(build, 2, MP_EMIT_BUILD_SLICE);
     }
 }
-
-STATIC void compile_subscript_2(compiler_t *comp, mp_parse_node_struct_t *pns) {
-    compile_node(comp, pns->nodes[0]); // start of slice
-    assert(MP_PARSE_NODE_IS_STRUCT(pns->nodes[1])); // should always be
-    compile_subscript_3_helper(comp, (mp_parse_node_struct_t*)pns->nodes[1]);
-}
-
-STATIC void compile_subscript_3(compiler_t *comp, mp_parse_node_struct_t *pns) {
-    EMIT_ARG(load_const_tok, MP_TOKEN_KW_NONE);
-    compile_subscript_3_helper(comp, pns);
-}
 #endif // MICROPY_PY_BUILTINS_SLICE
 
 STATIC void compile_dictorsetmaker_item(compiler_t *comp, mp_parse_node_struct_t *pns) {
@@ -2624,14 +2600,14 @@ STATIC void compile_yield_expr(compiler_t *comp, mp_parse_node_struct_t *pns) {
     }
     if (MP_PARSE_NODE_IS_NULL(pns->nodes[0])) {
         EMIT_ARG(load_const_tok, MP_TOKEN_KW_NONE);
-        EMIT(yield_value);
+        EMIT_ARG(yield, MP_EMIT_YIELD_VALUE);
     } else if (MP_PARSE_NODE_IS_STRUCT_KIND(pns->nodes[0], PN_yield_arg_from)) {
         pns = (mp_parse_node_struct_t*)pns->nodes[0];
         compile_node(comp, pns->nodes[0]);
         compile_yield_from(comp);
     } else {
         compile_node(comp, pns->nodes[0]);
-        EMIT(yield_value);
+        EMIT_ARG(yield, MP_EMIT_YIELD_VALUE);
     }
 }
 
@@ -2865,7 +2841,7 @@ STATIC void compile_scope_comp_iter(compiler_t *comp, mp_parse_node_struct_t *pn
         // no more nested if/for; compile inner expression
         compile_node(comp, pn_inner_expr);
         if (comp->scope_cur->kind == SCOPE_GEN_EXPR) {
-            EMIT(yield_value);
+            EMIT_ARG(yield, MP_EMIT_YIELD_VALUE);
             EMIT(pop_top);
         } else {
             EMIT_ARG(store_comp, comp->scope_cur->kind, 4 * for_depth + 5);
@@ -3043,19 +3019,19 @@ STATIC void compile_scope(compiler_t *comp, scope_t *scope, pass_kind_t pass) {
         }
 
         if (scope->kind == SCOPE_LIST_COMP) {
-            EMIT_ARG(build_list, 0);
+            EMIT_ARG(build, 0, MP_EMIT_BUILD_LIST);
         } else if (scope->kind == SCOPE_DICT_COMP) {
-            EMIT_ARG(build_map, 0);
+            EMIT_ARG(build, 0, MP_EMIT_BUILD_MAP);
         #if MICROPY_PY_BUILTINS_SET
         } else if (scope->kind == SCOPE_SET_COMP) {
-            EMIT_ARG(build_set, 0);
+            EMIT_ARG(build, 0, MP_EMIT_BUILD_SET);
         #endif
         }
 
         // There are 4 slots on the stack for the iterator, and the first one is
         // NULL to indicate that the second one points to the iterator object.
         if (scope->kind == SCOPE_GEN_EXPR) {
-            // TODO static assert that MP_OBJ_ITER_BUF_NSLOTS == 4
+            MP_STATIC_ASSERT(MP_OBJ_ITER_BUF_NSLOTS == 4);
             EMIT(load_null);
             compile_load_id(comp, qstr_arg);
             EMIT(load_null);
diff --git a/py/emit.h b/py/emit.h
index 270a40633..aa98efa77 100644
--- a/py/emit.h
+++ b/py/emit.h
@@ -55,13 +55,50 @@ typedef enum {
 #define MP_EMIT_NATIVE_TYPE_RETURN (1)
 #define MP_EMIT_NATIVE_TYPE_ARG    (2)
 
+// Kind for emit_id_ops->local()
+#define MP_EMIT_IDOP_LOCAL_FAST (0)
+#define MP_EMIT_IDOP_LOCAL_DEREF (1)
+
+// Kind for emit_id_ops->global()
+#define MP_EMIT_IDOP_GLOBAL_NAME (0)
+#define MP_EMIT_IDOP_GLOBAL_GLOBAL (1)
+
+// Kind for emit->import()
+#define MP_EMIT_IMPORT_NAME (0)
+#define MP_EMIT_IMPORT_FROM (1)
+#define MP_EMIT_IMPORT_STAR (2)
+
+// Kind for emit->subscr()
+#define MP_EMIT_SUBSCR_LOAD (0)
+#define MP_EMIT_SUBSCR_STORE (1)
+#define MP_EMIT_SUBSCR_DELETE (2)
+
+// Kind for emit->attr()
+#define MP_EMIT_ATTR_LOAD (0)
+#define MP_EMIT_ATTR_STORE (1)
+#define MP_EMIT_ATTR_DELETE (2)
+
+// Kind for emit->setup_block()
+#define MP_EMIT_SETUP_BLOCK_WITH (0)
+#define MP_EMIT_SETUP_BLOCK_EXCEPT (2)
+#define MP_EMIT_SETUP_BLOCK_FINALLY (3)
+
+// Kind for emit->build()
+#define MP_EMIT_BUILD_TUPLE (0)
+#define MP_EMIT_BUILD_LIST (1)
+#define MP_EMIT_BUILD_MAP (3)
+#define MP_EMIT_BUILD_SET (6)
+#define MP_EMIT_BUILD_SLICE (8)
+
+// Kind for emit->yield()
+#define MP_EMIT_YIELD_VALUE (0)
+#define MP_EMIT_YIELD_FROM (1)
+
 typedef struct _emit_t emit_t;
 
 typedef struct _mp_emit_method_table_id_ops_t {
-    void (*fast)(emit_t *emit, qstr qst, mp_uint_t local_num);
-    void (*deref)(emit_t *emit, qstr qst, mp_uint_t local_num);
-    void (*name)(emit_t *emit, qstr qst);
-    void (*global)(emit_t *emit, qstr qst);
+    void (*local)(emit_t *emit, qstr qst, mp_uint_t local_num, int kind);
+    void (*global)(emit_t *emit, qstr qst, int kind);
 } mp_emit_method_table_id_ops_t;
 
 typedef struct _emit_method_table_t {
@@ -77,22 +114,16 @@ typedef struct _emit_method_table_t {
     mp_emit_method_table_id_ops_t delete_id;
 
     void (*label_assign)(emit_t *emit, mp_uint_t l);
-    void (*import_name)(emit_t *emit, qstr qst);
-    void (*import_from)(emit_t *emit, qstr qst);
-    void (*import_star)(emit_t *emit);
+    void (*import)(emit_t *emit, qstr qst, int kind);
     void (*load_const_tok)(emit_t *emit, mp_token_kind_t tok);
     void (*load_const_small_int)(emit_t *emit, mp_int_t arg);
     void (*load_const_str)(emit_t *emit, qstr qst);
     void (*load_const_obj)(emit_t *emit, mp_obj_t obj);
     void (*load_null)(emit_t *emit);
-    void (*load_attr)(emit_t *emit, qstr qst);
     void (*load_method)(emit_t *emit, qstr qst, bool is_super);
     void (*load_build_class)(emit_t *emit);
-    void (*load_subscr)(emit_t *emit);
-    void (*store_attr)(emit_t *emit, qstr qst);
-    void (*store_subscr)(emit_t *emit);
-    void (*delete_attr)(emit_t *emit, qstr qst);
-    void (*delete_subscr)(emit_t *emit);
+    void (*subscr)(emit_t *emit, int kind);
+    void (*attr)(emit_t *emit, qstr qst, int kind);
     void (*dup_top)(emit_t *emit);
     void (*dup_top_two)(emit_t *emit);
     void (*pop_top)(emit_t *emit);
@@ -101,12 +132,9 @@ typedef struct _emit_method_table_t {
     void (*jump)(emit_t *emit, mp_uint_t label);
     void (*pop_jump_if)(emit_t *emit, bool cond, mp_uint_t label);
     void (*jump_if_or_pop)(emit_t *emit, bool cond, mp_uint_t label);
-    void (*break_loop)(emit_t *emit, mp_uint_t label, mp_uint_t except_depth);
-    void (*continue_loop)(emit_t *emit, mp_uint_t label, mp_uint_t except_depth);
-    void (*setup_with)(emit_t *emit, mp_uint_t label);
+    void (*unwind_jump)(emit_t *emit, mp_uint_t label, mp_uint_t except_depth);
+    void (*setup_block)(emit_t *emit, mp_uint_t label, int kind);
     void (*with_cleanup)(emit_t *emit, mp_uint_t label);
-    void (*setup_except)(emit_t *emit, mp_uint_t label);
-    void (*setup_finally)(emit_t *emit, mp_uint_t label);
     void (*end_finally)(emit_t *emit);
     void (*get_iter)(emit_t *emit, bool use_stack);
     void (*for_iter)(emit_t *emit, mp_uint_t label);
@@ -115,16 +143,8 @@ typedef struct _emit_method_table_t {
     void (*pop_except)(emit_t *emit);
     void (*unary_op)(emit_t *emit, mp_unary_op_t op);
     void (*binary_op)(emit_t *emit, mp_binary_op_t op);
-    void (*build_tuple)(emit_t *emit, mp_uint_t n_args);
-    void (*build_list)(emit_t *emit, mp_uint_t n_args);
-    void (*build_map)(emit_t *emit, mp_uint_t n_args);
+    void (*build)(emit_t *emit, mp_uint_t n_args, int kind);
     void (*store_map)(emit_t *emit);
-    #if MICROPY_PY_BUILTINS_SET
-    void (*build_set)(emit_t *emit, mp_uint_t n_args);
-    #endif
-    #if MICROPY_PY_BUILTINS_SLICE
-    void (*build_slice)(emit_t *emit, mp_uint_t n_args);
-    #endif
     void (*store_comp)(emit_t *emit, scope_kind_t kind, mp_uint_t set_stack_index);
     void (*unpack_sequence)(emit_t *emit, mp_uint_t n_args);
     void (*unpack_ex)(emit_t *emit, mp_uint_t n_left, mp_uint_t n_right);
@@ -134,8 +154,7 @@ typedef struct _emit_method_table_t {
     void (*call_method)(emit_t *emit, mp_uint_t n_positional, mp_uint_t n_keyword, mp_uint_t star_flags);
     void (*return_value)(emit_t *emit);
     void (*raise_varargs)(emit_t *emit, mp_uint_t n_args);
-    void (*yield_value)(emit_t *emit);
-    void (*yield_from)(emit_t *emit);
+    void (*yield)(emit_t *emit, int kind);
 
     // these methods are used to control entry to/exit from an exception handler
     // they may or may not emit code
@@ -180,36 +199,24 @@ bool mp_emit_bc_last_emit_was_return_value(emit_t *emit);
 void mp_emit_bc_adjust_stack_size(emit_t *emit, mp_int_t delta);
 void mp_emit_bc_set_source_line(emit_t *emit, mp_uint_t line);
 
-void mp_emit_bc_load_fast(emit_t *emit, qstr qst, mp_uint_t local_num);
-void mp_emit_bc_load_deref(emit_t *emit, qstr qst, mp_uint_t local_num);
-void mp_emit_bc_load_name(emit_t *emit, qstr qst);
-void mp_emit_bc_load_global(emit_t *emit, qstr qst);
-void mp_emit_bc_store_fast(emit_t *emit, qstr qst, mp_uint_t local_num);
-void mp_emit_bc_store_deref(emit_t *emit, qstr qst, mp_uint_t local_num);
-void mp_emit_bc_store_name(emit_t *emit, qstr qst);
-void mp_emit_bc_store_global(emit_t *emit, qstr qst);
-void mp_emit_bc_delete_fast(emit_t *emit, qstr qst, mp_uint_t local_num);
-void mp_emit_bc_delete_deref(emit_t *emit, qstr qst, mp_uint_t local_num);
-void mp_emit_bc_delete_name(emit_t *emit, qstr qst);
-void mp_emit_bc_delete_global(emit_t *emit, qstr qst);
+void mp_emit_bc_load_local(emit_t *emit, qstr qst, mp_uint_t local_num, int kind);
+void mp_emit_bc_load_global(emit_t *emit, qstr qst, int kind);
+void mp_emit_bc_store_local(emit_t *emit, qstr qst, mp_uint_t local_num, int kind);
+void mp_emit_bc_store_global(emit_t *emit, qstr qst, int kind);
+void mp_emit_bc_delete_local(emit_t *emit, qstr qst, mp_uint_t local_num, int kind);
+void mp_emit_bc_delete_global(emit_t *emit, qstr qst, int kind);
 
 void mp_emit_bc_label_assign(emit_t *emit, mp_uint_t l);
-void mp_emit_bc_import_name(emit_t *emit, qstr qst);
-void mp_emit_bc_import_from(emit_t *emit, qstr qst);
-void mp_emit_bc_import_star(emit_t *emit);
+void mp_emit_bc_import(emit_t *emit, qstr qst, int kind);
 void mp_emit_bc_load_const_tok(emit_t *emit, mp_token_kind_t tok);
 void mp_emit_bc_load_const_small_int(emit_t *emit, mp_int_t arg);
 void mp_emit_bc_load_const_str(emit_t *emit, qstr qst);
 void mp_emit_bc_load_const_obj(emit_t *emit, mp_obj_t obj);
 void mp_emit_bc_load_null(emit_t *emit);
-void mp_emit_bc_load_attr(emit_t *emit, qstr qst);
 void mp_emit_bc_load_method(emit_t *emit, qstr qst, bool is_super);
 void mp_emit_bc_load_build_class(emit_t *emit);
-void mp_emit_bc_load_subscr(emit_t *emit);
-void mp_emit_bc_store_attr(emit_t *emit, qstr qst);
-void mp_emit_bc_store_subscr(emit_t *emit);
-void mp_emit_bc_delete_attr(emit_t *emit, qstr qst);
-void mp_emit_bc_delete_subscr(emit_t *emit);
+void mp_emit_bc_subscr(emit_t *emit, int kind);
+void mp_emit_bc_attr(emit_t *emit, qstr qst, int kind);
 void mp_emit_bc_dup_top(emit_t *emit);
 void mp_emit_bc_dup_top_two(emit_t *emit);
 void mp_emit_bc_pop_top(emit_t *emit);
@@ -219,12 +226,8 @@ void mp_emit_bc_jump(emit_t *emit, mp_uint_t label);
 void mp_emit_bc_pop_jump_if(emit_t *emit, bool cond, mp_uint_t label);
 void mp_emit_bc_jump_if_or_pop(emit_t *emit, bool cond, mp_uint_t label);
 void mp_emit_bc_unwind_jump(emit_t *emit, mp_uint_t label, mp_uint_t except_depth);
-#define mp_emit_bc_break_loop mp_emit_bc_unwind_jump
-#define mp_emit_bc_continue_loop mp_emit_bc_unwind_jump
-void mp_emit_bc_setup_with(emit_t *emit, mp_uint_t label);
+void mp_emit_bc_setup_block(emit_t *emit, mp_uint_t label, int kind);
 void mp_emit_bc_with_cleanup(emit_t *emit, mp_uint_t label);
-void mp_emit_bc_setup_except(emit_t *emit, mp_uint_t label);
-void mp_emit_bc_setup_finally(emit_t *emit, mp_uint_t label);
 void mp_emit_bc_end_finally(emit_t *emit);
 void mp_emit_bc_get_iter(emit_t *emit, bool use_stack);
 void mp_emit_bc_for_iter(emit_t *emit, mp_uint_t label);
@@ -233,16 +236,8 @@ void mp_emit_bc_pop_block(emit_t *emit);
 void mp_emit_bc_pop_except(emit_t *emit);
 void mp_emit_bc_unary_op(emit_t *emit, mp_unary_op_t op);
 void mp_emit_bc_binary_op(emit_t *emit, mp_binary_op_t op);
-void mp_emit_bc_build_tuple(emit_t *emit, mp_uint_t n_args);
-void mp_emit_bc_build_list(emit_t *emit, mp_uint_t n_args);
-void mp_emit_bc_build_map(emit_t *emit, mp_uint_t n_args);
+void mp_emit_bc_build(emit_t *emit, mp_uint_t n_args, int kind);
 void mp_emit_bc_store_map(emit_t *emit);
-#if MICROPY_PY_BUILTINS_SET
-void mp_emit_bc_build_set(emit_t *emit, mp_uint_t n_args);
-#endif
-#if MICROPY_PY_BUILTINS_SLICE
-void mp_emit_bc_build_slice(emit_t *emit, mp_uint_t n_args);
-#endif
 void mp_emit_bc_store_comp(emit_t *emit, scope_kind_t kind, mp_uint_t list_stack_index);
 void mp_emit_bc_unpack_sequence(emit_t *emit, mp_uint_t n_args);
 void mp_emit_bc_unpack_ex(emit_t *emit, mp_uint_t n_left, mp_uint_t n_right);
@@ -252,8 +247,7 @@ void mp_emit_bc_call_function(emit_t *emit, mp_uint_t n_positional, mp_uint_t n_
 void mp_emit_bc_call_method(emit_t *emit, mp_uint_t n_positional, mp_uint_t n_keyword, mp_uint_t star_flags);
 void mp_emit_bc_return_value(emit_t *emit);
 void mp_emit_bc_raise_varargs(emit_t *emit, mp_uint_t n_args);
-void mp_emit_bc_yield_value(emit_t *emit);
-void mp_emit_bc_yield_from(emit_t *emit);
+void mp_emit_bc_yield(emit_t *emit, int kind);
 void mp_emit_bc_start_except_handler(emit_t *emit);
 void mp_emit_bc_end_except_handler(emit_t *emit);
 
diff --git a/py/emitbc.c b/py/emitbc.c
index 3f4dfc178..f3951e9cb 100644
--- a/py/emitbc.c
+++ b/py/emitbc.c
@@ -313,9 +313,12 @@ void mp_emit_bc_start_pass(emit_t *emit, pass_kind_t pass, scope_t *scope) {
     emit->scope = scope;
     emit->last_source_line_offset = 0;
     emit->last_source_line = 1;
-    if (pass < MP_PASS_EMIT) {
+    #ifndef NDEBUG
+    // With debugging enabled labels are checked for unique assignment
+    if (pass < MP_PASS_EMIT && emit->label_offsets != NULL) {
         memset(emit->label_offsets, -1, emit->max_num_labels * sizeof(mp_uint_t));
     }
+    #endif
     emit->bytecode_offset = 0;
     emit->code_info_offset = 0;
 
@@ -434,7 +437,9 @@ void mp_emit_bc_end_pass(emit_t *emit) {
 
     } else if (emit->pass == MP_PASS_EMIT) {
         mp_emit_glue_assign_bytecode(emit->scope->raw_code, emit->code_base,
+            #if MICROPY_PERSISTENT_CODE_SAVE || MICROPY_DEBUG_PRINTERS
             emit->code_info_size + emit->bytecode_size,
+            #endif
             emit->const_table,
             #if MICROPY_PERSISTENT_CODE_SAVE
             emit->ct_cur_obj, emit->ct_cur_raw_code,
@@ -495,24 +500,23 @@ void mp_emit_bc_label_assign(emit_t *emit, mp_uint_t l) {
         emit->label_offsets[l] = emit->bytecode_offset;
     } else {
         // ensure label offset has not changed from MP_PASS_CODE_SIZE to MP_PASS_EMIT
-        //printf("l%d: (at %d vs %d)\n", l, emit->bytecode_offset, emit->label_offsets[l]);
         assert(emit->label_offsets[l] == emit->bytecode_offset);
     }
 }
 
-void mp_emit_bc_import_name(emit_t *emit, qstr qst) {
-    emit_bc_pre(emit, -1);
-    emit_write_bytecode_byte_qstr(emit, MP_BC_IMPORT_NAME, qst);
-}
-
-void mp_emit_bc_import_from(emit_t *emit, qstr qst) {
-    emit_bc_pre(emit, 1);
-    emit_write_bytecode_byte_qstr(emit, MP_BC_IMPORT_FROM, qst);
-}
-
-void mp_emit_bc_import_star(emit_t *emit) {
-    emit_bc_pre(emit, -1);
-    emit_write_bytecode_byte(emit, MP_BC_IMPORT_STAR);
+void mp_emit_bc_import(emit_t *emit, qstr qst, int kind) {
+    MP_STATIC_ASSERT(MP_BC_IMPORT_NAME + MP_EMIT_IMPORT_NAME == MP_BC_IMPORT_NAME);
+    MP_STATIC_ASSERT(MP_BC_IMPORT_NAME + MP_EMIT_IMPORT_FROM == MP_BC_IMPORT_FROM);
+    if (kind == MP_EMIT_IMPORT_FROM) {
+        emit_bc_pre(emit, 1);
+    } else {
+        emit_bc_pre(emit, -1);
+    }
+    if (kind == MP_EMIT_IMPORT_STAR) {
+        emit_write_bytecode_byte(emit, MP_BC_IMPORT_STAR);
+    } else {
+        emit_write_bytecode_byte_qstr(emit, MP_BC_IMPORT_NAME + kind, qst);
+    }
 }
 
 void mp_emit_bc_load_const_tok(emit_t *emit, mp_token_kind_t tok) {
@@ -552,43 +556,24 @@ void mp_emit_bc_load_null(emit_t *emit) {
     emit_write_bytecode_byte(emit, MP_BC_LOAD_NULL);
 }
 
-void mp_emit_bc_load_fast(emit_t *emit, qstr qst, mp_uint_t local_num) {
+void mp_emit_bc_load_local(emit_t *emit, qstr qst, mp_uint_t local_num, int kind) {
+    MP_STATIC_ASSERT(MP_BC_LOAD_FAST_N + MP_EMIT_IDOP_LOCAL_FAST == MP_BC_LOAD_FAST_N);
+    MP_STATIC_ASSERT(MP_BC_LOAD_FAST_N + MP_EMIT_IDOP_LOCAL_DEREF == MP_BC_LOAD_DEREF);
     (void)qst;
     emit_bc_pre(emit, 1);
-    if (local_num <= 15) {
+    if (kind == MP_EMIT_IDOP_LOCAL_FAST && local_num <= 15) {
         emit_write_bytecode_byte(emit, MP_BC_LOAD_FAST_MULTI + local_num);
     } else {
-        emit_write_bytecode_byte_uint(emit, MP_BC_LOAD_FAST_N, local_num);
-    }
-}
-
-void mp_emit_bc_load_deref(emit_t *emit, qstr qst, mp_uint_t local_num) {
-    (void)qst;
-    emit_bc_pre(emit, 1);
-    emit_write_bytecode_byte_uint(emit, MP_BC_LOAD_DEREF, local_num);
-}
-
-void mp_emit_bc_load_name(emit_t *emit, qstr qst) {
-    (void)qst;
-    emit_bc_pre(emit, 1);
-    emit_write_bytecode_byte_qstr(emit, MP_BC_LOAD_NAME, qst);
-    if (MICROPY_OPT_CACHE_MAP_LOOKUP_IN_BYTECODE_DYNAMIC) {
-        emit_write_bytecode_byte(emit, 0);
+        emit_write_bytecode_byte_uint(emit, MP_BC_LOAD_FAST_N + kind, local_num);
     }
 }
 
-void mp_emit_bc_load_global(emit_t *emit, qstr qst) {
+void mp_emit_bc_load_global(emit_t *emit, qstr qst, int kind) {
+    MP_STATIC_ASSERT(MP_BC_LOAD_NAME + MP_EMIT_IDOP_GLOBAL_NAME == MP_BC_LOAD_NAME);
+    MP_STATIC_ASSERT(MP_BC_LOAD_NAME + MP_EMIT_IDOP_GLOBAL_GLOBAL == MP_BC_LOAD_GLOBAL);
     (void)qst;
     emit_bc_pre(emit, 1);
-    emit_write_bytecode_byte_qstr(emit, MP_BC_LOAD_GLOBAL, qst);
-    if (MICROPY_OPT_CACHE_MAP_LOOKUP_IN_BYTECODE_DYNAMIC) {
-        emit_write_bytecode_byte(emit, 0);
-    }
-}
-
-void mp_emit_bc_load_attr(emit_t *emit, qstr qst) {
-    emit_bc_pre(emit, 0);
-    emit_write_bytecode_byte_qstr(emit, MP_BC_LOAD_ATTR, qst);
+    emit_write_bytecode_byte_qstr(emit, MP_BC_LOAD_NAME + kind, qst);
     if (MICROPY_OPT_CACHE_MAP_LOOKUP_IN_BYTECODE_DYNAMIC) {
         emit_write_bytecode_byte(emit, 0);
     }
@@ -604,80 +589,68 @@ void mp_emit_bc_load_build_class(emit_t *emit) {
     emit_write_bytecode_byte(emit, MP_BC_LOAD_BUILD_CLASS);
 }
 
-void mp_emit_bc_load_subscr(emit_t *emit) {
-    emit_bc_pre(emit, -1);
-    emit_write_bytecode_byte(emit, MP_BC_LOAD_SUBSCR);
-}
-
-void mp_emit_bc_store_fast(emit_t *emit, qstr qst, mp_uint_t local_num) {
-    (void)qst;
-    emit_bc_pre(emit, -1);
-    if (local_num <= 15) {
-        emit_write_bytecode_byte(emit, MP_BC_STORE_FAST_MULTI + local_num);
+void mp_emit_bc_subscr(emit_t *emit, int kind) {
+    if (kind == MP_EMIT_SUBSCR_LOAD) {
+        emit_bc_pre(emit, -1);
+        emit_write_bytecode_byte(emit, MP_BC_LOAD_SUBSCR);
     } else {
-        emit_write_bytecode_byte_uint(emit, MP_BC_STORE_FAST_N, local_num);
+        if (kind == MP_EMIT_SUBSCR_DELETE) {
+            mp_emit_bc_load_null(emit);
+            mp_emit_bc_rot_three(emit);
+        }
+        emit_bc_pre(emit, -3);
+        emit_write_bytecode_byte(emit, MP_BC_STORE_SUBSCR);
     }
 }
 
-void mp_emit_bc_store_deref(emit_t *emit, qstr qst, mp_uint_t local_num) {
-    (void)qst;
-    emit_bc_pre(emit, -1);
-    emit_write_bytecode_byte_uint(emit, MP_BC_STORE_DEREF, local_num);
-}
-
-void mp_emit_bc_store_name(emit_t *emit, qstr qst) {
-    emit_bc_pre(emit, -1);
-    emit_write_bytecode_byte_qstr(emit, MP_BC_STORE_NAME, qst);
-}
-
-void mp_emit_bc_store_global(emit_t *emit, qstr qst) {
-    emit_bc_pre(emit, -1);
-    emit_write_bytecode_byte_qstr(emit, MP_BC_STORE_GLOBAL, qst);
-}
-
-void mp_emit_bc_store_attr(emit_t *emit, qstr qst) {
-    emit_bc_pre(emit, -2);
-    emit_write_bytecode_byte_qstr(emit, MP_BC_STORE_ATTR, qst);
+void mp_emit_bc_attr(emit_t *emit, qstr qst, int kind) {
+    if (kind == MP_EMIT_ATTR_LOAD) {
+        emit_bc_pre(emit, 0);
+        emit_write_bytecode_byte_qstr(emit, MP_BC_LOAD_ATTR, qst);
+    } else {
+        if (kind == MP_EMIT_ATTR_DELETE) {
+            mp_emit_bc_load_null(emit);
+            mp_emit_bc_rot_two(emit);
+        }
+        emit_bc_pre(emit, -2);
+        emit_write_bytecode_byte_qstr(emit, MP_BC_STORE_ATTR, qst);
+    }
     if (MICROPY_OPT_CACHE_MAP_LOOKUP_IN_BYTECODE_DYNAMIC) {
         emit_write_bytecode_byte(emit, 0);
     }
 }
 
-void mp_emit_bc_store_subscr(emit_t *emit) {
-    emit_bc_pre(emit, -3);
-    emit_write_bytecode_byte(emit, MP_BC_STORE_SUBSCR);
-}
-
-void mp_emit_bc_delete_fast(emit_t *emit, qstr qst, mp_uint_t local_num) {
+void mp_emit_bc_store_local(emit_t *emit, qstr qst, mp_uint_t local_num, int kind) {
+    MP_STATIC_ASSERT(MP_BC_STORE_FAST_N + MP_EMIT_IDOP_LOCAL_FAST == MP_BC_STORE_FAST_N);
+    MP_STATIC_ASSERT(MP_BC_STORE_FAST_N + MP_EMIT_IDOP_LOCAL_DEREF == MP_BC_STORE_DEREF);
     (void)qst;
-    emit_write_bytecode_byte_uint(emit, MP_BC_DELETE_FAST, local_num);
+    emit_bc_pre(emit, -1);
+    if (kind == MP_EMIT_IDOP_LOCAL_FAST && local_num <= 15) {
+        emit_write_bytecode_byte(emit, MP_BC_STORE_FAST_MULTI + local_num);
+    } else {
+        emit_write_bytecode_byte_uint(emit, MP_BC_STORE_FAST_N + kind, local_num);
+    }
 }
 
-void mp_emit_bc_delete_deref(emit_t *emit, qstr qst, mp_uint_t local_num) {
-    (void)qst;
-    emit_write_bytecode_byte_uint(emit, MP_BC_DELETE_DEREF, local_num);
+void mp_emit_bc_store_global(emit_t *emit, qstr qst, int kind) {
+    MP_STATIC_ASSERT(MP_BC_STORE_NAME + MP_EMIT_IDOP_GLOBAL_NAME == MP_BC_STORE_NAME);
+    MP_STATIC_ASSERT(MP_BC_STORE_NAME + MP_EMIT_IDOP_GLOBAL_GLOBAL == MP_BC_STORE_GLOBAL);
+    emit_bc_pre(emit, -1);
+    emit_write_bytecode_byte_qstr(emit, MP_BC_STORE_NAME + kind, qst);
 }
 
-void mp_emit_bc_delete_name(emit_t *emit, qstr qst) {
-    emit_bc_pre(emit, 0);
-    emit_write_bytecode_byte_qstr(emit, MP_BC_DELETE_NAME, qst);
+void mp_emit_bc_delete_local(emit_t *emit, qstr qst, mp_uint_t local_num, int kind) {
+    MP_STATIC_ASSERT(MP_BC_DELETE_FAST + MP_EMIT_IDOP_LOCAL_FAST == MP_BC_DELETE_FAST);
+    MP_STATIC_ASSERT(MP_BC_DELETE_FAST + MP_EMIT_IDOP_LOCAL_DEREF == MP_BC_DELETE_DEREF);
+    (void)qst;
+    emit_write_bytecode_byte_uint(emit, MP_BC_DELETE_FAST + kind, local_num);
 }
 
-void mp_emit_bc_delete_global(emit_t *emit, qstr qst) {
+void mp_emit_bc_delete_global(emit_t *emit, qstr qst, int kind) {
+    MP_STATIC_ASSERT(MP_BC_DELETE_NAME + MP_EMIT_IDOP_GLOBAL_NAME == MP_BC_DELETE_NAME);
+    MP_STATIC_ASSERT(MP_BC_DELETE_NAME + MP_EMIT_IDOP_GLOBAL_GLOBAL == MP_BC_DELETE_GLOBAL);
     emit_bc_pre(emit, 0);
-    emit_write_bytecode_byte_qstr(emit, MP_BC_DELETE_GLOBAL, qst);
-}
-
-void mp_emit_bc_delete_attr(emit_t *emit, qstr qst) {
-    mp_emit_bc_load_null(emit);
-    mp_emit_bc_rot_two(emit);
-    mp_emit_bc_store_attr(emit, qst);
-}
-
-void mp_emit_bc_delete_subscr(emit_t *emit) {
-    mp_emit_bc_load_null(emit);
-    mp_emit_bc_rot_three(emit);
-    mp_emit_bc_store_subscr(emit);
+    emit_write_bytecode_byte_qstr(emit, MP_BC_DELETE_NAME + kind, qst);
 }
 
 void mp_emit_bc_dup_top(emit_t *emit) {
@@ -746,11 +719,18 @@ void mp_emit_bc_unwind_jump(emit_t *emit, mp_uint_t label, mp_uint_t except_dept
     }
 }
 
-void mp_emit_bc_setup_with(emit_t *emit, mp_uint_t label) {
+void mp_emit_bc_setup_block(emit_t *emit, mp_uint_t label, int kind) {
+    MP_STATIC_ASSERT(MP_BC_SETUP_WITH + MP_EMIT_SETUP_BLOCK_WITH == MP_BC_SETUP_WITH);
+    MP_STATIC_ASSERT(MP_BC_SETUP_WITH + MP_EMIT_SETUP_BLOCK_EXCEPT == MP_BC_SETUP_EXCEPT);
+    MP_STATIC_ASSERT(MP_BC_SETUP_WITH + MP_EMIT_SETUP_BLOCK_FINALLY == MP_BC_SETUP_FINALLY);
+    if (kind == MP_EMIT_SETUP_BLOCK_WITH) {
     // The SETUP_WITH opcode pops ctx_mgr from the top of the stack
     // and then pushes 3 entries: __exit__, ctx_mgr, as_value.
-    emit_bc_pre(emit, 2);
-    emit_write_bytecode_byte_unsigned_label(emit, MP_BC_SETUP_WITH, label);
+        emit_bc_pre(emit, 2);
+    } else {
+        emit_bc_pre(emit, 0);
+    }
+    emit_write_bytecode_byte_unsigned_label(emit, MP_BC_SETUP_WITH + kind, label);
 }
 
 void mp_emit_bc_with_cleanup(emit_t *emit, mp_uint_t label) {
@@ -759,17 +739,7 @@ void mp_emit_bc_with_cleanup(emit_t *emit, mp_uint_t label) {
     mp_emit_bc_label_assign(emit, label);
     emit_bc_pre(emit, 2); // ensure we have enough stack space to call the __exit__ method
     emit_write_bytecode_byte(emit, MP_BC_WITH_CLEANUP);
-    emit_bc_pre(emit, -4); // cancel the 2 above, plus the 2 from mp_emit_bc_setup_with
-}
-
-void mp_emit_bc_setup_except(emit_t *emit, mp_uint_t label) {
-    emit_bc_pre(emit, 0);
-    emit_write_bytecode_byte_unsigned_label(emit, MP_BC_SETUP_EXCEPT, label);
-}
-
-void mp_emit_bc_setup_finally(emit_t *emit, mp_uint_t label) {
-    emit_bc_pre(emit, 0);
-    emit_write_bytecode_byte_unsigned_label(emit, MP_BC_SETUP_FINALLY, label);
+    emit_bc_pre(emit, -4); // cancel the 2 above, plus the 2 from mp_emit_bc_setup_block(MP_EMIT_SETUP_BLOCK_WITH)
 }
 
 void mp_emit_bc_end_finally(emit_t *emit) {
@@ -823,19 +793,18 @@ void mp_emit_bc_binary_op(emit_t *emit, mp_binary_op_t op) {
     }
 }
 
-void mp_emit_bc_build_tuple(emit_t *emit, mp_uint_t n_args) {
-    emit_bc_pre(emit, 1 - n_args);
-    emit_write_bytecode_byte_uint(emit, MP_BC_BUILD_TUPLE, n_args);
-}
-
-void mp_emit_bc_build_list(emit_t *emit, mp_uint_t n_args) {
-    emit_bc_pre(emit, 1 - n_args);
-    emit_write_bytecode_byte_uint(emit, MP_BC_BUILD_LIST, n_args);
-}
-
-void mp_emit_bc_build_map(emit_t *emit, mp_uint_t n_args) {
-    emit_bc_pre(emit, 1);
-    emit_write_bytecode_byte_uint(emit, MP_BC_BUILD_MAP, n_args);
+void mp_emit_bc_build(emit_t *emit, mp_uint_t n_args, int kind) {
+    MP_STATIC_ASSERT(MP_BC_BUILD_TUPLE + MP_EMIT_BUILD_TUPLE == MP_BC_BUILD_TUPLE);
+    MP_STATIC_ASSERT(MP_BC_BUILD_TUPLE + MP_EMIT_BUILD_LIST == MP_BC_BUILD_LIST);
+    MP_STATIC_ASSERT(MP_BC_BUILD_TUPLE + MP_EMIT_BUILD_MAP == MP_BC_BUILD_MAP);
+    MP_STATIC_ASSERT(MP_BC_BUILD_TUPLE + MP_EMIT_BUILD_SET == MP_BC_BUILD_SET);
+    MP_STATIC_ASSERT(MP_BC_BUILD_TUPLE + MP_EMIT_BUILD_SLICE == MP_BC_BUILD_SLICE);
+    if (kind == MP_EMIT_BUILD_MAP) {
+        emit_bc_pre(emit, 1);
+    } else {
+        emit_bc_pre(emit, 1 - n_args);
+    }
+    emit_write_bytecode_byte_uint(emit, MP_BC_BUILD_TUPLE + kind, n_args);
 }
 
 void mp_emit_bc_store_map(emit_t *emit) {
@@ -843,20 +812,6 @@ void mp_emit_bc_store_map(emit_t *emit) {
     emit_write_bytecode_byte(emit, MP_BC_STORE_MAP);
 }
 
-#if MICROPY_PY_BUILTINS_SET
-void mp_emit_bc_build_set(emit_t *emit, mp_uint_t n_args) {
-    emit_bc_pre(emit, 1 - n_args);
-    emit_write_bytecode_byte_uint(emit, MP_BC_BUILD_SET, n_args);
-}
-#endif
-
-#if MICROPY_PY_BUILTINS_SLICE
-void mp_emit_bc_build_slice(emit_t *emit, mp_uint_t n_args) {
-    emit_bc_pre(emit, 1 - n_args);
-    emit_write_bytecode_byte_uint(emit, MP_BC_BUILD_SLICE, n_args);
-}
-#endif
-
 void mp_emit_bc_store_comp(emit_t *emit, scope_kind_t kind, mp_uint_t collection_stack_index) {
     int t;
     int n;
@@ -938,16 +893,11 @@ void mp_emit_bc_raise_varargs(emit_t *emit, mp_uint_t n_args) {
     emit_write_bytecode_byte_byte(emit, MP_BC_RAISE_VARARGS, n_args);
 }
 
-void mp_emit_bc_yield_value(emit_t *emit) {
-    emit_bc_pre(emit, 0);
-    emit->scope->scope_flags |= MP_SCOPE_FLAG_GENERATOR;
-    emit_write_bytecode_byte(emit, MP_BC_YIELD_VALUE);
-}
-
-void mp_emit_bc_yield_from(emit_t *emit) {
-    emit_bc_pre(emit, -1);
+void mp_emit_bc_yield(emit_t *emit, int kind) {
+    MP_STATIC_ASSERT(MP_BC_YIELD_VALUE + 1 == MP_BC_YIELD_FROM);
+    emit_bc_pre(emit, -kind);
     emit->scope->scope_flags |= MP_SCOPE_FLAG_GENERATOR;
-    emit_write_bytecode_byte(emit, MP_BC_YIELD_FROM);
+    emit_write_bytecode_byte(emit, MP_BC_YIELD_VALUE + kind);
 }
 
 void mp_emit_bc_start_except_handler(emit_t *emit) {
@@ -968,41 +918,29 @@ const emit_method_table_t emit_bc_method_table = {
     mp_emit_bc_set_source_line,
 
     {
-        mp_emit_bc_load_fast,
-        mp_emit_bc_load_deref,
-        mp_emit_bc_load_name,
+        mp_emit_bc_load_local,
         mp_emit_bc_load_global,
     },
     {
-        mp_emit_bc_store_fast,
-        mp_emit_bc_store_deref,
-        mp_emit_bc_store_name,
+        mp_emit_bc_store_local,
         mp_emit_bc_store_global,
     },
     {
-        mp_emit_bc_delete_fast,
-        mp_emit_bc_delete_deref,
-        mp_emit_bc_delete_name,
+        mp_emit_bc_delete_local,
         mp_emit_bc_delete_global,
     },
 
     mp_emit_bc_label_assign,
-    mp_emit_bc_import_name,
-    mp_emit_bc_import_from,
-    mp_emit_bc_import_star,
+    mp_emit_bc_import,
     mp_emit_bc_load_const_tok,
     mp_emit_bc_load_const_small_int,
     mp_emit_bc_load_const_str,
     mp_emit_bc_load_const_obj,
     mp_emit_bc_load_null,
-    mp_emit_bc_load_attr,
     mp_emit_bc_load_method,
     mp_emit_bc_load_build_class,
-    mp_emit_bc_load_subscr,
-    mp_emit_bc_store_attr,
-    mp_emit_bc_store_subscr,
-    mp_emit_bc_delete_attr,
-    mp_emit_bc_delete_subscr,
+    mp_emit_bc_subscr,
+    mp_emit_bc_attr,
     mp_emit_bc_dup_top,
     mp_emit_bc_dup_top_two,
     mp_emit_bc_pop_top,
@@ -1012,11 +950,8 @@ const emit_method_table_t emit_bc_method_table = {
     mp_emit_bc_pop_jump_if,
     mp_emit_bc_jump_if_or_pop,
     mp_emit_bc_unwind_jump,
-    mp_emit_bc_unwind_jump,
-    mp_emit_bc_setup_with,
+    mp_emit_bc_setup_block,
     mp_emit_bc_with_cleanup,
-    mp_emit_bc_setup_except,
-    mp_emit_bc_setup_finally,
     mp_emit_bc_end_finally,
     mp_emit_bc_get_iter,
     mp_emit_bc_for_iter,
@@ -1025,16 +960,8 @@ const emit_method_table_t emit_bc_method_table = {
     mp_emit_bc_pop_except,
     mp_emit_bc_unary_op,
     mp_emit_bc_binary_op,
-    mp_emit_bc_build_tuple,
-    mp_emit_bc_build_list,
-    mp_emit_bc_build_map,
+    mp_emit_bc_build,
     mp_emit_bc_store_map,
-    #if MICROPY_PY_BUILTINS_SET
-    mp_emit_bc_build_set,
-    #endif
-    #if MICROPY_PY_BUILTINS_SLICE
-    mp_emit_bc_build_slice,
-    #endif
     mp_emit_bc_store_comp,
     mp_emit_bc_unpack_sequence,
     mp_emit_bc_unpack_ex,
@@ -1044,31 +971,24 @@ const emit_method_table_t emit_bc_method_table = {
     mp_emit_bc_call_method,
     mp_emit_bc_return_value,
     mp_emit_bc_raise_varargs,
-    mp_emit_bc_yield_value,
-    mp_emit_bc_yield_from,
+    mp_emit_bc_yield,
 
     mp_emit_bc_start_except_handler,
     mp_emit_bc_end_except_handler,
 };
 #else
 const mp_emit_method_table_id_ops_t mp_emit_bc_method_table_load_id_ops = {
-    mp_emit_bc_load_fast,
-    mp_emit_bc_load_deref,
-    mp_emit_bc_load_name,
+    mp_emit_bc_load_local,
     mp_emit_bc_load_global,
 };
 
 const mp_emit_method_table_id_ops_t mp_emit_bc_method_table_store_id_ops = {
-    mp_emit_bc_store_fast,
-    mp_emit_bc_store_deref,
-    mp_emit_bc_store_name,
+    mp_emit_bc_store_local,
     mp_emit_bc_store_global,
 };
 
 const mp_emit_method_table_id_ops_t mp_emit_bc_method_table_delete_id_ops = {
-    mp_emit_bc_delete_fast,
-    mp_emit_bc_delete_deref,
-    mp_emit_bc_delete_name,
+    mp_emit_bc_delete_local,
     mp_emit_bc_delete_global,
 };
 #endif
diff --git a/py/emitcommon.c b/py/emitcommon.c
index 07b1dbb4c..89cc2c959 100644
--- a/py/emitcommon.c
+++ b/py/emitcommon.c
@@ -63,14 +63,14 @@ void mp_emit_common_id_op(emit_t *emit, const mp_emit_method_table_id_ops_t *emi
 
     // call the emit backend with the correct code
     if (id->kind == ID_INFO_KIND_GLOBAL_IMPLICIT) {
-        emit_method_table->name(emit, qst);
+        emit_method_table->global(emit, qst, MP_EMIT_IDOP_GLOBAL_NAME);
     } else if (id->kind == ID_INFO_KIND_GLOBAL_EXPLICIT) {
-        emit_method_table->global(emit, qst);
+        emit_method_table->global(emit, qst, MP_EMIT_IDOP_GLOBAL_GLOBAL);
     } else if (id->kind == ID_INFO_KIND_LOCAL) {
-        emit_method_table->fast(emit, qst, id->local_num);
+        emit_method_table->local(emit, qst, id->local_num, MP_EMIT_IDOP_LOCAL_FAST);
     } else {
         assert(id->kind == ID_INFO_KIND_CELL || id->kind == ID_INFO_KIND_FREE);
-        emit_method_table->deref(emit, qst, id->local_num);
+        emit_method_table->local(emit, qst, id->local_num, MP_EMIT_IDOP_LOCAL_DEREF);
     }
 }
 
diff --git a/py/emitglue.c b/py/emitglue.c
index d2add988f..74bf8ddca 100644
--- a/py/emitglue.c
+++ b/py/emitglue.c
@@ -55,7 +55,10 @@ mp_raw_code_t *mp_emit_glue_new_raw_code(void) {
     return rc;
 }
 
-void mp_emit_glue_assign_bytecode(mp_raw_code_t *rc, const byte *code, mp_uint_t len,
+void mp_emit_glue_assign_bytecode(mp_raw_code_t *rc, const byte *code,
+    #if MICROPY_PERSISTENT_CODE_SAVE || MICROPY_DEBUG_PRINTERS
+    size_t len,
+    #endif
     const mp_uint_t *const_table,
     #if MICROPY_PERSISTENT_CODE_SAVE
     uint16_t n_obj, uint16_t n_raw_code,
diff --git a/py/emitglue.h b/py/emitglue.h
index 43930333d..0830a0d5c 100644
--- a/py/emitglue.h
+++ b/py/emitglue.h
@@ -40,7 +40,7 @@ typedef enum {
 } mp_raw_code_kind_t;
 
 typedef struct _mp_raw_code_t {
-    mp_raw_code_kind_t kind : 3;
+    mp_uint_t kind : 3; // of type mp_raw_code_kind_t
     mp_uint_t scope_flags : 7;
     mp_uint_t n_pos_args : 11;
     union {
@@ -63,7 +63,10 @@ typedef struct _mp_raw_code_t {
 
 mp_raw_code_t *mp_emit_glue_new_raw_code(void);
 
-void mp_emit_glue_assign_bytecode(mp_raw_code_t *rc, const byte *code, mp_uint_t len,
+void mp_emit_glue_assign_bytecode(mp_raw_code_t *rc, const byte *code,
+    #if MICROPY_PERSISTENT_CODE_SAVE || MICROPY_DEBUG_PRINTERS
+    size_t len,
+    #endif
     const mp_uint_t *const_table,
     #if MICROPY_PERSISTENT_CODE_SAVE
     uint16_t n_obj, uint16_t n_raw_code,
diff --git a/py/emitnarm.c b/py/emitnarm.c
new file mode 100644
index 000000000..1b585f821
--- /dev/null
+++ b/py/emitnarm.c
@@ -0,0 +1,15 @@
+// ARM specific stuff
+
+#include "py/mpconfig.h"
+
+#if MICROPY_EMIT_ARM
+
+// This is defined so that the assembler exports generic assembler API macros
+#define GENERIC_ASM_API (1)
+#include "py/asmarm.h"
+
+#define N_ARM (1)
+#define EXPORT_FUN(name) emit_native_arm_##name
+#include "py/emitnative.c"
+
+#endif
diff --git a/py/emitnative.c b/py/emitnative.c
index 8e97dda11..ad8f04aac 100644
--- a/py/emitnative.c
+++ b/py/emitnative.c
@@ -57,102 +57,14 @@
 #endif
 
 // wrapper around everything in this file
-#if (MICROPY_EMIT_X64 && N_X64) \
-    || (MICROPY_EMIT_X86 && N_X86) \
-    || (MICROPY_EMIT_THUMB && N_THUMB) \
-    || (MICROPY_EMIT_ARM && N_ARM) \
-    || (MICROPY_EMIT_XTENSA && N_XTENSA) \
-
-// this is defined so that the assembler exports generic assembler API macros
-#define GENERIC_ASM_API (1)
-
-#if N_X64
-
-// x64 specific stuff
-#include "py/asmx64.h"
-#define EXPORT_FUN(name) emit_native_x64_##name
-
-#elif N_X86
-
-// x86 specific stuff
-
-STATIC byte mp_f_n_args[MP_F_NUMBER_OF] = {
-    [MP_F_CONVERT_OBJ_TO_NATIVE] = 2,
-    [MP_F_CONVERT_NATIVE_TO_OBJ] = 2,
-    [MP_F_LOAD_NAME] = 1,
-    [MP_F_LOAD_GLOBAL] = 1,
-    [MP_F_LOAD_BUILD_CLASS] = 0,
-    [MP_F_LOAD_ATTR] = 2,
-    [MP_F_LOAD_METHOD] = 3,
-    [MP_F_LOAD_SUPER_METHOD] = 2,
-    [MP_F_STORE_NAME] = 2,
-    [MP_F_STORE_GLOBAL] = 2,
-    [MP_F_STORE_ATTR] = 3,
-    [MP_F_OBJ_SUBSCR] = 3,
-    [MP_F_OBJ_IS_TRUE] = 1,
-    [MP_F_UNARY_OP] = 2,
-    [MP_F_BINARY_OP] = 3,
-    [MP_F_BUILD_TUPLE] = 2,
-    [MP_F_BUILD_LIST] = 2,
-    [MP_F_LIST_APPEND] = 2,
-    [MP_F_BUILD_MAP] = 1,
-    [MP_F_STORE_MAP] = 3,
-#if MICROPY_PY_BUILTINS_SET
-    [MP_F_BUILD_SET] = 2,
-    [MP_F_STORE_SET] = 2,
-#endif
-    [MP_F_MAKE_FUNCTION_FROM_RAW_CODE] = 3,
-    [MP_F_NATIVE_CALL_FUNCTION_N_KW] = 3,
-    [MP_F_CALL_METHOD_N_KW] = 3,
-    [MP_F_CALL_METHOD_N_KW_VAR] = 3,
-    [MP_F_NATIVE_GETITER] = 2,
-    [MP_F_NATIVE_ITERNEXT] = 1,
-    [MP_F_NLR_PUSH] = 1,
-    [MP_F_NLR_POP] = 0,
-    [MP_F_NATIVE_RAISE] = 1,
-    [MP_F_IMPORT_NAME] = 3,
-    [MP_F_IMPORT_FROM] = 2,
-    [MP_F_IMPORT_ALL] = 1,
-#if MICROPY_PY_BUILTINS_SLICE
-    [MP_F_NEW_SLICE] = 3,
-#endif
-    [MP_F_UNPACK_SEQUENCE] = 3,
-    [MP_F_UNPACK_EX] = 3,
-    [MP_F_DELETE_NAME] = 1,
-    [MP_F_DELETE_GLOBAL] = 1,
-    [MP_F_NEW_CELL] = 1,
-    [MP_F_MAKE_CLOSURE_FROM_RAW_CODE] = 3,
-    [MP_F_SETUP_CODE_STATE] = 5,
-    [MP_F_SMALL_INT_FLOOR_DIVIDE] = 2,
-    [MP_F_SMALL_INT_MODULO] = 2,
-};
-
-#include "py/asmx86.h"
-#define EXPORT_FUN(name) emit_native_x86_##name
-
-#elif N_THUMB
-
-// thumb specific stuff
-#include "py/asmthumb.h"
-#define EXPORT_FUN(name) emit_native_thumb_##name
-
-#elif N_ARM
-
-// ARM specific stuff
-#include "py/asmarm.h"
-#define EXPORT_FUN(name) emit_native_arm_##name
-
-#elif N_XTENSA
-
-// Xtensa specific stuff
-#include "py/asmxtensa.h"
-#define EXPORT_FUN(name) emit_native_xtensa_##name
-
-#else
-
-#error unknown native emitter
+#if N_X64 || N_X86 || N_THUMB || N_ARM || N_XTENSA
 
-#endif
+// define additional generic helper macros
+#define ASM_MOV_LOCAL_IMM_VIA(as, local_num, imm, reg_temp) \
+    do { \
+        ASM_MOV_REG_IMM((as), (reg_temp), (imm)); \
+        ASM_MOV_LOCAL_REG((as), (local_num), (reg_temp)); \
+    } while (false)
 
 #define EMIT_NATIVE_VIPER_TYPE_ERROR(emit, ...) do { \
         *emit->error_slot = mp_obj_new_exception_msg_varg(&mp_type_ViperTypeError, __VA_ARGS__); \
@@ -389,7 +301,7 @@ STATIC void emit_native_start_pass(emit_t *emit, pass_kind_t pass, scope_t *scop
                 ASM_MOV_REG_REG(emit->as, REG_LOCAL_3, REG_ARG_3);
             } else {
                 assert(i == 3); // should be true; max 4 args is checked above
-                ASM_MOV_REG_TO_LOCAL(emit->as, REG_ARG_4, i - REG_LOCAL_NUM);
+                ASM_MOV_LOCAL_REG(emit->as, i - REG_LOCAL_NUM, REG_ARG_4);
             }
         }
         #endif
@@ -418,14 +330,14 @@ STATIC void emit_native_start_pass(emit_t *emit, pass_kind_t pass, scope_t *scop
         #endif
 
         // set code_state.fun_bc
-        ASM_MOV_REG_TO_LOCAL(emit->as, REG_ARG_1, offsetof(mp_code_state_t, fun_bc) / sizeof(uintptr_t));
+        ASM_MOV_LOCAL_REG(emit->as, offsetof(mp_code_state_t, fun_bc) / sizeof(uintptr_t), REG_ARG_1);
 
         // set code_state.ip (offset from start of this function to prelude info)
         // XXX this encoding may change size
-        ASM_MOV_IMM_TO_LOCAL_USING(emit->as, emit->prelude_offset, offsetof(mp_code_state_t, ip) / sizeof(uintptr_t), REG_ARG_1);
+        ASM_MOV_LOCAL_IMM_VIA(emit->as, offsetof(mp_code_state_t, ip) / sizeof(uintptr_t), emit->prelude_offset, REG_ARG_1);
 
         // put address of code_state into first arg
-        ASM_MOV_LOCAL_ADDR_TO_REG(emit->as, 0, REG_ARG_1);
+        ASM_MOV_REG_LOCAL_ADDR(emit->as, REG_ARG_1, 0);
 
         // call mp_setup_code_state to prepare code_state structure
         #if N_THUMB
@@ -438,11 +350,11 @@ STATIC void emit_native_start_pass(emit_t *emit, pass_kind_t pass, scope_t *scop
 
         // cache some locals in registers
         if (scope->num_locals > 0) {
-            ASM_MOV_LOCAL_TO_REG(emit->as, STATE_START + emit->n_state - 1 - 0, REG_LOCAL_1);
+            ASM_MOV_REG_LOCAL(emit->as, REG_LOCAL_1, STATE_START + emit->n_state - 1 - 0);
             if (scope->num_locals > 1) {
-                ASM_MOV_LOCAL_TO_REG(emit->as, STATE_START + emit->n_state - 1 - 1, REG_LOCAL_2);
+                ASM_MOV_REG_LOCAL(emit->as, REG_LOCAL_2, STATE_START + emit->n_state - 1 - 1);
                 if (scope->num_locals > 2) {
-                    ASM_MOV_LOCAL_TO_REG(emit->as, STATE_START + emit->n_state - 1 - 2, REG_LOCAL_3);
+                    ASM_MOV_REG_LOCAL(emit->as, REG_LOCAL_3, STATE_START + emit->n_state - 1 - 2);
                 }
             }
         }
@@ -606,7 +518,7 @@ STATIC void need_reg_single(emit_t *emit, int reg_needed, int skip_stack_pos) {
             stack_info_t *si = &emit->stack_info[i];
             if (si->kind == STACK_REG && si->data.u_reg == reg_needed) {
                 si->kind = STACK_VALUE;
-                ASM_MOV_REG_TO_LOCAL(emit->as, si->data.u_reg, emit->stack_start + i);
+                ASM_MOV_LOCAL_REG(emit->as, emit->stack_start + i, si->data.u_reg);
             }
         }
     }
@@ -617,7 +529,7 @@ STATIC void need_reg_all(emit_t *emit) {
         stack_info_t *si = &emit->stack_info[i];
         if (si->kind == STACK_REG) {
             si->kind = STACK_VALUE;
-            ASM_MOV_REG_TO_LOCAL(emit->as, si->data.u_reg, emit->stack_start + i);
+            ASM_MOV_LOCAL_REG(emit->as, emit->stack_start + i, si->data.u_reg);
         }
     }
 }
@@ -629,7 +541,7 @@ STATIC void need_stack_settled(emit_t *emit) {
         if (si->kind == STACK_REG) {
             DEBUG_printf("    reg(%u) to local(%u)\n", si->data.u_reg, emit->stack_start + i);
             si->kind = STACK_VALUE;
-            ASM_MOV_REG_TO_LOCAL(emit->as, si->data.u_reg, emit->stack_start + i);
+            ASM_MOV_LOCAL_REG(emit->as, emit->stack_start + i, si->data.u_reg);
         }
     }
     for (int i = 0; i < emit->stack_size; i++) {
@@ -637,7 +549,7 @@ STATIC void need_stack_settled(emit_t *emit) {
         if (si->kind == STACK_IMM) {
             DEBUG_printf("    imm(" INT_FMT ") to local(%u)\n", si->data.u_imm, emit->stack_start + i);
             si->kind = STACK_VALUE;
-            ASM_MOV_IMM_TO_LOCAL_USING(emit->as, si->data.u_imm, emit->stack_start + i, REG_TEMP0);
+            ASM_MOV_LOCAL_IMM_VIA(emit->as, emit->stack_start + i, si->data.u_imm, REG_TEMP0);
         }
     }
 }
@@ -649,7 +561,7 @@ STATIC void emit_access_stack(emit_t *emit, int pos, vtype_kind_t *vtype, int re
     *vtype = si->vtype;
     switch (si->kind) {
         case STACK_VALUE:
-            ASM_MOV_LOCAL_TO_REG(emit->as, emit->stack_start + emit->stack_size - pos, reg_dest);
+            ASM_MOV_REG_LOCAL(emit->as, reg_dest, emit->stack_start + emit->stack_size - pos);
             break;
 
         case STACK_REG:
@@ -659,7 +571,7 @@ STATIC void emit_access_stack(emit_t *emit, int pos, vtype_kind_t *vtype, int re
             break;
 
         case STACK_IMM:
-            ASM_MOV_IMM_TO_REG(emit->as, si->data.u_imm, reg_dest);
+            ASM_MOV_REG_IMM(emit->as, reg_dest, si->data.u_imm);
             break;
     }
 }
@@ -671,7 +583,7 @@ STATIC void emit_fold_stack_top(emit_t *emit, int reg_dest) {
     si[0] = si[1];
     if (si->kind == STACK_VALUE) {
         // if folded element was on the stack we need to put it in a register
-        ASM_MOV_LOCAL_TO_REG(emit->as, emit->stack_start + emit->stack_size - 1, reg_dest);
+        ASM_MOV_REG_LOCAL(emit->as, reg_dest, emit->stack_start + emit->stack_size - 1);
         si->kind = STACK_REG;
         si->data.u_reg = reg_dest;
     }
@@ -765,30 +677,30 @@ STATIC void emit_call(emit_t *emit, mp_fun_kind_t fun_kind) {
 
 STATIC void emit_call_with_imm_arg(emit_t *emit, mp_fun_kind_t fun_kind, mp_int_t arg_val, int arg_reg) {
     need_reg_all(emit);
-    ASM_MOV_IMM_TO_REG(emit->as, arg_val, arg_reg);
+    ASM_MOV_REG_IMM(emit->as, arg_reg, arg_val);
     ASM_CALL_IND(emit->as, mp_fun_table[fun_kind], fun_kind);
 }
 
 // the first arg is stored in the code aligned on a mp_uint_t boundary
 STATIC void emit_call_with_imm_arg_aligned(emit_t *emit, mp_fun_kind_t fun_kind, mp_int_t arg_val, int arg_reg) {
     need_reg_all(emit);
-    ASM_MOV_ALIGNED_IMM_TO_REG(emit->as, arg_val, arg_reg);
+    ASM_MOV_REG_ALIGNED_IMM(emit->as, arg_reg, arg_val);
     ASM_CALL_IND(emit->as, mp_fun_table[fun_kind], fun_kind);
 }
 
 STATIC void emit_call_with_2_imm_args(emit_t *emit, mp_fun_kind_t fun_kind, mp_int_t arg_val1, int arg_reg1, mp_int_t arg_val2, int arg_reg2) {
     need_reg_all(emit);
-    ASM_MOV_IMM_TO_REG(emit->as, arg_val1, arg_reg1);
-    ASM_MOV_IMM_TO_REG(emit->as, arg_val2, arg_reg2);
+    ASM_MOV_REG_IMM(emit->as, arg_reg1, arg_val1);
+    ASM_MOV_REG_IMM(emit->as, arg_reg2, arg_val2);
     ASM_CALL_IND(emit->as, mp_fun_table[fun_kind], fun_kind);
 }
 
 // the first arg is stored in the code aligned on a mp_uint_t boundary
 STATIC void emit_call_with_3_imm_args_and_first_aligned(emit_t *emit, mp_fun_kind_t fun_kind, mp_int_t arg_val1, int arg_reg1, mp_int_t arg_val2, int arg_reg2, mp_int_t arg_val3, int arg_reg3) {
     need_reg_all(emit);
-    ASM_MOV_ALIGNED_IMM_TO_REG(emit->as, arg_val1, arg_reg1);
-    ASM_MOV_IMM_TO_REG(emit->as, arg_val2, arg_reg2);
-    ASM_MOV_IMM_TO_REG(emit->as, arg_val3, arg_reg3);
+    ASM_MOV_REG_ALIGNED_IMM(emit->as, arg_reg1, arg_val1);
+    ASM_MOV_REG_IMM(emit->as, arg_reg2, arg_val2);
+    ASM_MOV_REG_IMM(emit->as, arg_reg3, arg_val3);
     ASM_CALL_IND(emit->as, mp_fun_table[fun_kind], fun_kind);
 }
 
@@ -808,19 +720,19 @@ STATIC void emit_get_stack_pointer_to_reg_for_pop(emit_t *emit, mp_uint_t reg_de
             si->kind = STACK_VALUE;
             switch (si->vtype) {
                 case VTYPE_PYOBJ:
-                    ASM_MOV_IMM_TO_LOCAL_USING(emit->as, si->data.u_imm, emit->stack_start + emit->stack_size - 1 - i, reg_dest);
+                    ASM_MOV_LOCAL_IMM_VIA(emit->as, emit->stack_start + emit->stack_size - 1 - i, si->data.u_imm, reg_dest);
                     break;
                 case VTYPE_BOOL:
                     if (si->data.u_imm == 0) {
-                        ASM_MOV_IMM_TO_LOCAL_USING(emit->as, (mp_uint_t)mp_const_false, emit->stack_start + emit->stack_size - 1 - i, reg_dest);
+                        ASM_MOV_LOCAL_IMM_VIA(emit->as, emit->stack_start + emit->stack_size - 1 - i, (mp_uint_t)mp_const_false, reg_dest);
                     } else {
-                        ASM_MOV_IMM_TO_LOCAL_USING(emit->as, (mp_uint_t)mp_const_true, emit->stack_start + emit->stack_size - 1 - i, reg_dest);
+                        ASM_MOV_LOCAL_IMM_VIA(emit->as, emit->stack_start + emit->stack_size - 1 - i, (mp_uint_t)mp_const_true, reg_dest);
                     }
                     si->vtype = VTYPE_PYOBJ;
                     break;
                 case VTYPE_INT:
                 case VTYPE_UINT:
-                    ASM_MOV_IMM_TO_LOCAL_USING(emit->as, (uintptr_t)MP_OBJ_NEW_SMALL_INT(si->data.u_imm), emit->stack_start + emit->stack_size - 1 - i, reg_dest);
+                    ASM_MOV_LOCAL_IMM_VIA(emit->as, emit->stack_start + emit->stack_size - 1 - i, (uintptr_t)MP_OBJ_NEW_SMALL_INT(si->data.u_imm), reg_dest);
                     si->vtype = VTYPE_PYOBJ;
                     break;
                 default:
@@ -838,9 +750,9 @@ STATIC void emit_get_stack_pointer_to_reg_for_pop(emit_t *emit, mp_uint_t reg_de
         stack_info_t *si = &emit->stack_info[emit->stack_size - 1 - i];
         if (si->vtype != VTYPE_PYOBJ) {
             mp_uint_t local_num = emit->stack_start + emit->stack_size - 1 - i;
-            ASM_MOV_LOCAL_TO_REG(emit->as, local_num, REG_ARG_1);
+            ASM_MOV_REG_LOCAL(emit->as, REG_ARG_1, local_num);
             emit_call_with_imm_arg(emit, MP_F_CONVERT_NATIVE_TO_OBJ, si->vtype, REG_ARG_2); // arg2 = type
-            ASM_MOV_REG_TO_LOCAL(emit->as, REG_RET, local_num);
+            ASM_MOV_LOCAL_REG(emit->as, local_num, REG_RET);
             si->vtype = VTYPE_PYOBJ;
             DEBUG_printf("  convert_native_to_obj(local_num=" UINT_FMT ")\n", local_num);
         }
@@ -848,7 +760,7 @@ STATIC void emit_get_stack_pointer_to_reg_for_pop(emit_t *emit, mp_uint_t reg_de
 
     // Adujust the stack for a pop of n_pop items, and load the stack pointer into reg_dest.
     adjust_stack(emit, -n_pop);
-    ASM_MOV_LOCAL_ADDR_TO_REG(emit->as, emit->stack_start + emit->stack_size, reg_dest);
+    ASM_MOV_REG_LOCAL_ADDR(emit->as, reg_dest, emit->stack_start + emit->stack_size);
 }
 
 // vtype of all n_push objects is VTYPE_PYOBJ
@@ -858,7 +770,7 @@ STATIC void emit_get_stack_pointer_to_reg_for_push(emit_t *emit, mp_uint_t reg_d
         emit->stack_info[emit->stack_size + i].kind = STACK_VALUE;
         emit->stack_info[emit->stack_size + i].vtype = VTYPE_PYOBJ;
     }
-    ASM_MOV_LOCAL_ADDR_TO_REG(emit->as, emit->stack_start + emit->stack_size, reg_dest);
+    ASM_MOV_REG_LOCAL_ADDR(emit->as, reg_dest, emit->stack_start + emit->stack_size);
     adjust_stack(emit, n_push);
 }
 
@@ -881,7 +793,7 @@ STATIC void emit_native_import_name(emit_t *emit, qstr qst) {
         stack_info_t *top = peek_stack(emit, 0);
         if (top->vtype == VTYPE_PTR_NONE) {
             emit_pre_pop_discard(emit);
-            ASM_MOV_IMM_TO_REG(emit->as, (mp_uint_t)mp_const_none, REG_ARG_2);
+            ASM_MOV_REG_IMM(emit->as, REG_ARG_2, (mp_uint_t)mp_const_none);
         } else {
             vtype_kind_t vtype_fromlist;
             emit_pre_pop_reg(emit, &vtype_fromlist, REG_ARG_2);
@@ -891,7 +803,7 @@ STATIC void emit_native_import_name(emit_t *emit, qstr qst) {
         // level argument should be an immediate integer
         top = peek_stack(emit, 0);
         assert(top->vtype == VTYPE_INT && top->kind == STACK_IMM);
-        ASM_MOV_IMM_TO_REG(emit->as, (mp_uint_t)MP_OBJ_NEW_SMALL_INT(top->data.u_imm), REG_ARG_3);
+        ASM_MOV_REG_IMM(emit->as, REG_ARG_3, (mp_uint_t)MP_OBJ_NEW_SMALL_INT(top->data.u_imm));
         emit_pre_pop_discard(emit);
 
     } else {
@@ -925,6 +837,16 @@ STATIC void emit_native_import_star(emit_t *emit) {
     emit_post(emit);
 }
 
+STATIC void emit_native_import(emit_t *emit, qstr qst, int kind) {
+    if (kind == MP_EMIT_IMPORT_NAME) {
+        emit_native_import_name(emit, qst);
+    } else if (kind == MP_EMIT_IMPORT_FROM) {
+        emit_native_import_from(emit, qst);
+    } else {
+        emit_native_import_star(emit);
+    }
+}
+
 STATIC void emit_native_load_const_tok(emit_t *emit, mp_token_kind_t tok) {
     DEBUG_printf("load_const_tok(tok=%u)\n", tok);
     emit_native_pre(emit);
@@ -981,7 +903,7 @@ STATIC void emit_native_load_const_str(emit_t *emit, qstr qst) {
 STATIC void emit_native_load_const_obj(emit_t *emit, mp_obj_t obj) {
     emit_native_pre(emit);
     need_reg_single(emit, REG_RET, 0);
-    ASM_MOV_ALIGNED_IMM_TO_REG(emit->as, (mp_uint_t)obj, REG_RET);
+    ASM_MOV_REG_ALIGNED_IMM(emit->as, REG_RET, (mp_uint_t)obj);
     emit_post_push_reg(emit, VTYPE_PYOBJ, REG_RET);
 }
 
@@ -1006,9 +928,9 @@ STATIC void emit_native_load_fast(emit_t *emit, qstr qst, mp_uint_t local_num) {
     } else {
         need_reg_single(emit, REG_TEMP0, 0);
         if (emit->do_viper_types) {
-            ASM_MOV_LOCAL_TO_REG(emit->as, local_num - REG_LOCAL_NUM, REG_TEMP0);
+            ASM_MOV_REG_LOCAL(emit->as, REG_TEMP0, local_num - REG_LOCAL_NUM);
         } else {
-            ASM_MOV_LOCAL_TO_REG(emit->as, STATE_START + emit->n_state - 1 - local_num, REG_TEMP0);
+            ASM_MOV_REG_LOCAL(emit->as, REG_TEMP0, STATE_START + emit->n_state - 1 - local_num);
         }
         emit_post_push_reg(emit, vtype, REG_TEMP0);
     }
@@ -1026,33 +948,47 @@ STATIC void emit_native_load_deref(emit_t *emit, qstr qst, mp_uint_t local_num)
     emit_post_push_reg(emit, VTYPE_PYOBJ, REG_RET);
 }
 
-STATIC void emit_native_load_name(emit_t *emit, qstr qst) {
-    DEBUG_printf("load_name(%s)\n", qstr_str(qst));
-    emit_native_pre(emit);
-    emit_call_with_imm_arg(emit, MP_F_LOAD_NAME, qst, REG_ARG_1);
-    emit_post_push_reg(emit, VTYPE_PYOBJ, REG_RET);
+STATIC void emit_native_load_local(emit_t *emit, qstr qst, mp_uint_t local_num, int kind) {
+    if (kind == MP_EMIT_IDOP_LOCAL_FAST) {
+        emit_native_load_fast(emit, qst, local_num);
+    } else {
+        emit_native_load_deref(emit, qst, local_num);
+    }
 }
 
-STATIC void emit_native_load_global(emit_t *emit, qstr qst) {
-    DEBUG_printf("load_global(%s)\n", qstr_str(qst));
+STATIC void emit_native_load_global(emit_t *emit, qstr qst, int kind) {
+    MP_STATIC_ASSERT(MP_F_LOAD_NAME + MP_EMIT_IDOP_GLOBAL_NAME == MP_F_LOAD_NAME);
+    MP_STATIC_ASSERT(MP_F_LOAD_NAME + MP_EMIT_IDOP_GLOBAL_GLOBAL == MP_F_LOAD_GLOBAL);
     emit_native_pre(emit);
-    // check for builtin casting operators
-    if (emit->do_viper_types && qst == MP_QSTR_int) {
-        emit_post_push_imm(emit, VTYPE_BUILTIN_CAST, VTYPE_INT);
-    } else if (emit->do_viper_types && qst == MP_QSTR_uint) {
-        emit_post_push_imm(emit, VTYPE_BUILTIN_CAST, VTYPE_UINT);
-    } else if (emit->do_viper_types && qst == MP_QSTR_ptr) {
-        emit_post_push_imm(emit, VTYPE_BUILTIN_CAST, VTYPE_PTR);
-    } else if (emit->do_viper_types && qst == MP_QSTR_ptr8) {
-        emit_post_push_imm(emit, VTYPE_BUILTIN_CAST, VTYPE_PTR8);
-    } else if (emit->do_viper_types && qst == MP_QSTR_ptr16) {
-        emit_post_push_imm(emit, VTYPE_BUILTIN_CAST, VTYPE_PTR16);
-    } else if (emit->do_viper_types && qst == MP_QSTR_ptr32) {
-        emit_post_push_imm(emit, VTYPE_BUILTIN_CAST, VTYPE_PTR32);
+    if (kind == MP_EMIT_IDOP_GLOBAL_NAME) {
+        DEBUG_printf("load_name(%s)\n", qstr_str(qst));
     } else {
-        emit_call_with_imm_arg(emit, MP_F_LOAD_GLOBAL, qst, REG_ARG_1);
-        emit_post_push_reg(emit, VTYPE_PYOBJ, REG_RET);
+        DEBUG_printf("load_global(%s)\n", qstr_str(qst));
+        if (emit->do_viper_types) {
+            // check for builtin casting operators
+            if (qst == MP_QSTR_int) {
+                emit_post_push_imm(emit, VTYPE_BUILTIN_CAST, VTYPE_INT);
+                return;
+            } else if (qst == MP_QSTR_uint) {
+                emit_post_push_imm(emit, VTYPE_BUILTIN_CAST, VTYPE_UINT);
+                return;
+            } else if (qst == MP_QSTR_ptr) {
+                emit_post_push_imm(emit, VTYPE_BUILTIN_CAST, VTYPE_PTR);
+                return;
+            } else if (qst == MP_QSTR_ptr8) {
+                emit_post_push_imm(emit, VTYPE_BUILTIN_CAST, VTYPE_PTR8);
+                return;
+            } else if (qst == MP_QSTR_ptr16) {
+                emit_post_push_imm(emit, VTYPE_BUILTIN_CAST, VTYPE_PTR16);
+                return;
+            } else if (qst == MP_QSTR_ptr32) {
+                emit_post_push_imm(emit, VTYPE_BUILTIN_CAST, VTYPE_PTR32);
+                return;
+            }
+        }
     }
+    emit_call_with_imm_arg(emit, MP_F_LOAD_NAME + kind, qst, REG_ARG_1);
+    emit_post_push_reg(emit, VTYPE_PYOBJ, REG_RET);
 }
 
 STATIC void emit_native_load_attr(emit_t *emit, qstr qst) {
@@ -1134,7 +1070,7 @@ STATIC void emit_native_load_subscr(emit_t *emit) {
                             break;
                         }
                         #endif
-                        ASM_MOV_IMM_TO_REG(emit->as, index_value, reg_index);
+                        ASM_MOV_REG_IMM(emit->as, reg_index, index_value);
                         ASM_ADD_REG_REG(emit->as, reg_index, reg_base); // add index to base
                         reg_base = reg_index;
                     }
@@ -1151,7 +1087,7 @@ STATIC void emit_native_load_subscr(emit_t *emit) {
                             break;
                         }
                         #endif
-                        ASM_MOV_IMM_TO_REG(emit->as, index_value << 1, reg_index);
+                        ASM_MOV_REG_IMM(emit->as, reg_index, index_value << 1);
                         ASM_ADD_REG_REG(emit->as, reg_index, reg_base); // add 2*index to base
                         reg_base = reg_index;
                     }
@@ -1168,7 +1104,7 @@ STATIC void emit_native_load_subscr(emit_t *emit) {
                             break;
                         }
                         #endif
-                        ASM_MOV_IMM_TO_REG(emit->as, index_value << 2, reg_index);
+                        ASM_MOV_REG_IMM(emit->as, reg_index, index_value << 2);
                         ASM_ADD_REG_REG(emit->as, reg_index, reg_base); // add 4*index to base
                         reg_base = reg_index;
                     }
@@ -1233,9 +1169,9 @@ STATIC void emit_native_store_fast(emit_t *emit, qstr qst, mp_uint_t local_num)
     } else {
         emit_pre_pop_reg(emit, &vtype, REG_TEMP0);
         if (emit->do_viper_types) {
-            ASM_MOV_REG_TO_LOCAL(emit->as, REG_TEMP0, local_num - REG_LOCAL_NUM);
+            ASM_MOV_LOCAL_REG(emit->as, local_num - REG_LOCAL_NUM, REG_TEMP0);
         } else {
-            ASM_MOV_REG_TO_LOCAL(emit->as, REG_TEMP0, STATE_START + emit->n_state - 1 - local_num);
+            ASM_MOV_LOCAL_REG(emit->as, STATE_START + emit->n_state - 1 - local_num, REG_TEMP0);
         }
     }
     emit_post(emit);
@@ -1266,25 +1202,33 @@ STATIC void emit_native_store_deref(emit_t *emit, qstr qst, mp_uint_t local_num)
     emit_post(emit);
 }
 
-STATIC void emit_native_store_name(emit_t *emit, qstr qst) {
-    // mp_store_name, but needs conversion of object (maybe have mp_viper_store_name(obj, type))
-    vtype_kind_t vtype;
-    emit_pre_pop_reg(emit, &vtype, REG_ARG_2);
-    assert(vtype == VTYPE_PYOBJ);
-    emit_call_with_imm_arg(emit, MP_F_STORE_NAME, qst, REG_ARG_1); // arg1 = name
-    emit_post(emit);
+STATIC void emit_native_store_local(emit_t *emit, qstr qst, mp_uint_t local_num, int kind) {
+    if (kind == MP_EMIT_IDOP_LOCAL_FAST) {
+        emit_native_store_fast(emit, qst, local_num);
+    } else {
+        emit_native_store_deref(emit, qst, local_num);
+    }
 }
 
-STATIC void emit_native_store_global(emit_t *emit, qstr qst) {
-    vtype_kind_t vtype = peek_vtype(emit, 0);
-    if (vtype == VTYPE_PYOBJ) {
+STATIC void emit_native_store_global(emit_t *emit, qstr qst, int kind) {
+    MP_STATIC_ASSERT(MP_F_STORE_NAME + MP_EMIT_IDOP_GLOBAL_NAME == MP_F_STORE_NAME);
+    MP_STATIC_ASSERT(MP_F_STORE_NAME + MP_EMIT_IDOP_GLOBAL_GLOBAL == MP_F_STORE_GLOBAL);
+    if (kind == MP_EMIT_IDOP_GLOBAL_NAME) {
+        // mp_store_name, but needs conversion of object (maybe have mp_viper_store_name(obj, type))
+        vtype_kind_t vtype;
         emit_pre_pop_reg(emit, &vtype, REG_ARG_2);
+        assert(vtype == VTYPE_PYOBJ);
     } else {
-        emit_pre_pop_reg(emit, &vtype, REG_ARG_1);
-        emit_call_with_imm_arg(emit, MP_F_CONVERT_NATIVE_TO_OBJ, vtype, REG_ARG_2); // arg2 = type
-        ASM_MOV_REG_REG(emit->as, REG_ARG_2, REG_RET);
+        vtype_kind_t vtype = peek_vtype(emit, 0);
+        if (vtype == VTYPE_PYOBJ) {
+            emit_pre_pop_reg(emit, &vtype, REG_ARG_2);
+        } else {
+            emit_pre_pop_reg(emit, &vtype, REG_ARG_1);
+            emit_call_with_imm_arg(emit, MP_F_CONVERT_NATIVE_TO_OBJ, vtype, REG_ARG_2); // arg2 = type
+            ASM_MOV_REG_REG(emit->as, REG_ARG_2, REG_RET);
+        }
     }
-    emit_call_with_imm_arg(emit, MP_F_STORE_GLOBAL, qst, REG_ARG_1); // arg1 = name
+    emit_call_with_imm_arg(emit, MP_F_STORE_NAME + kind, qst, REG_ARG_1); // arg1 = name
     emit_post(emit);
 }
 
@@ -1354,7 +1298,7 @@ STATIC void emit_native_store_subscr(emit_t *emit) {
                             break;
                         }
                         #endif
-                        ASM_MOV_IMM_TO_REG(emit->as, index_value, reg_index);
+                        ASM_MOV_REG_IMM(emit->as, reg_index, index_value);
                         #if N_ARM
                         asm_arm_strb_reg_reg_reg(emit->as, reg_value, reg_base, reg_index);
                         return;
@@ -1375,7 +1319,7 @@ STATIC void emit_native_store_subscr(emit_t *emit) {
                             break;
                         }
                         #endif
-                        ASM_MOV_IMM_TO_REG(emit->as, index_value << 1, reg_index);
+                        ASM_MOV_REG_IMM(emit->as, reg_index, index_value << 1);
                         #if N_ARM
                         asm_arm_strh_reg_reg_reg(emit->as, reg_value, reg_base, reg_index);
                         return;
@@ -1396,7 +1340,7 @@ STATIC void emit_native_store_subscr(emit_t *emit) {
                             break;
                         }
                         #endif
-                        ASM_MOV_IMM_TO_REG(emit->as, index_value << 2, reg_index);
+                        ASM_MOV_REG_IMM(emit->as, reg_index, index_value << 2);
                         #if N_ARM
                         asm_arm_str_reg_reg_reg(emit->as, reg_value, reg_base, reg_index);
                         return;
@@ -1477,30 +1421,23 @@ STATIC void emit_native_store_subscr(emit_t *emit) {
     }
 }
 
-STATIC void emit_native_delete_fast(emit_t *emit, qstr qst, mp_uint_t local_num) {
-    // TODO: This is not compliant implementation. We could use MP_OBJ_SENTINEL
-    // to mark deleted vars but then every var would need to be checked on
-    // each access. Very inefficient, so just set value to None to enable GC.
-    emit_native_load_const_tok(emit, MP_TOKEN_KW_NONE);
-    emit_native_store_fast(emit, qst, local_num);
-}
-
-STATIC void emit_native_delete_deref(emit_t *emit, qstr qst, mp_uint_t local_num) {
-    // TODO implement me!
-    (void)emit;
-    (void)qst;
-    (void)local_num;
-}
-
-STATIC void emit_native_delete_name(emit_t *emit, qstr qst) {
-    emit_native_pre(emit);
-    emit_call_with_imm_arg(emit, MP_F_DELETE_NAME, qst, REG_ARG_1);
-    emit_post(emit);
+STATIC void emit_native_delete_local(emit_t *emit, qstr qst, mp_uint_t local_num, int kind) {
+    if (kind == MP_EMIT_IDOP_LOCAL_FAST) {
+        // TODO: This is not compliant implementation. We could use MP_OBJ_SENTINEL
+        // to mark deleted vars but then every var would need to be checked on
+        // each access. Very inefficient, so just set value to None to enable GC.
+        emit_native_load_const_tok(emit, MP_TOKEN_KW_NONE);
+        emit_native_store_fast(emit, qst, local_num);
+    } else {
+        // TODO implement me!
+    }
 }
 
-STATIC void emit_native_delete_global(emit_t *emit, qstr qst) {
+STATIC void emit_native_delete_global(emit_t *emit, qstr qst, int kind) {
+    MP_STATIC_ASSERT(MP_F_DELETE_NAME + MP_EMIT_IDOP_GLOBAL_NAME == MP_F_DELETE_NAME);
+    MP_STATIC_ASSERT(MP_F_DELETE_NAME + MP_EMIT_IDOP_GLOBAL_GLOBAL == MP_F_DELETE_GLOBAL);
     emit_native_pre(emit);
-    emit_call_with_imm_arg(emit, MP_F_DELETE_GLOBAL, qst, REG_ARG_1);
+    emit_call_with_imm_arg(emit, MP_F_DELETE_NAME + kind, qst, REG_ARG_1);
     emit_post(emit);
 }
 
@@ -1520,6 +1457,26 @@ STATIC void emit_native_delete_subscr(emit_t *emit) {
     emit_call_with_imm_arg(emit, MP_F_OBJ_SUBSCR, (mp_uint_t)MP_OBJ_NULL, REG_ARG_3);
 }
 
+STATIC void emit_native_subscr(emit_t *emit, int kind) {
+    if (kind == MP_EMIT_SUBSCR_LOAD) {
+        emit_native_load_subscr(emit);
+    } else if (kind == MP_EMIT_SUBSCR_STORE) {
+        emit_native_store_subscr(emit);
+    } else {
+        emit_native_delete_subscr(emit);
+    }
+}
+
+STATIC void emit_native_attr(emit_t *emit, qstr qst, int kind) {
+    if (kind == MP_EMIT_ATTR_LOAD) {
+        emit_native_load_attr(emit, qst);
+    } else if (kind == MP_EMIT_ATTR_STORE) {
+        emit_native_store_attr(emit, qst);
+    } else {
+        emit_native_delete_attr(emit, qst);
+    }
+}
+
 STATIC void emit_native_dup_top(emit_t *emit) {
     DEBUG_printf("dup_top\n");
     vtype_kind_t vtype;
@@ -1613,16 +1570,11 @@ STATIC void emit_native_jump_if_or_pop(emit_t *emit, bool cond, mp_uint_t label)
     emit_post(emit);
 }
 
-STATIC void emit_native_break_loop(emit_t *emit, mp_uint_t label, mp_uint_t except_depth) {
+STATIC void emit_native_unwind_jump(emit_t *emit, mp_uint_t label, mp_uint_t except_depth) {
     (void)except_depth;
     emit_native_jump(emit, label & ~MP_EMIT_BREAK_FROM_FOR); // TODO properly
 }
 
-STATIC void emit_native_continue_loop(emit_t *emit, mp_uint_t label, mp_uint_t except_depth) {
-    (void)except_depth;
-    emit_native_jump(emit, label); // TODO properly
-}
-
 STATIC void emit_native_setup_with(emit_t *emit, mp_uint_t label) {
     // the context manager is on the top of the stack
     // stack: (..., ctx_mgr)
@@ -1665,6 +1617,21 @@ STATIC void emit_native_setup_with(emit_t *emit, mp_uint_t label) {
     // stack: (..., __exit__, self, as_value, nlr_buf, as_value)
 }
 
+STATIC void emit_native_setup_block(emit_t *emit, mp_uint_t label, int kind) {
+    if (kind == MP_EMIT_SETUP_BLOCK_WITH) {
+        emit_native_setup_with(emit, label);
+    } else {
+        // Set up except and finally
+        emit_native_pre(emit);
+        // need to commit stack because we may jump elsewhere
+        need_stack_settled(emit);
+        emit_get_stack_pointer_to_reg_for_push(emit, REG_ARG_1, sizeof(nlr_buf_t) / sizeof(mp_uint_t)); // arg1 = pointer to nlr buf
+        emit_call(emit, MP_F_NLR_PUSH);
+        ASM_JUMP_IF_REG_NONZERO(emit->as, REG_RET, label);
+        emit_post(emit);
+    }
+}
+
 STATIC void emit_native_with_cleanup(emit_t *emit, mp_uint_t label) {
     // note: label+1 is available as an auxiliary label
 
@@ -1734,20 +1701,6 @@ STATIC void emit_native_with_cleanup(emit_t *emit, mp_uint_t label) {
     emit_native_label_assign(emit, label + 1);
 }
 
-STATIC void emit_native_setup_except(emit_t *emit, mp_uint_t label) {
-    emit_native_pre(emit);
-    // need to commit stack because we may jump elsewhere
-    need_stack_settled(emit);
-    emit_get_stack_pointer_to_reg_for_push(emit, REG_ARG_1, sizeof(nlr_buf_t) / sizeof(mp_uint_t)); // arg1 = pointer to nlr buf
-    emit_call(emit, MP_F_NLR_PUSH);
-    ASM_JUMP_IF_REG_NONZERO(emit->as, REG_RET, label);
-    emit_post(emit);
-}
-
-STATIC void emit_native_setup_finally(emit_t *emit, mp_uint_t label) {
-    emit_native_setup_except(emit, label);
-}
-
 STATIC void emit_native_end_finally(emit_t *emit) {
     // logic:
     //   exc = pop_stack
@@ -1773,7 +1726,7 @@ STATIC void emit_native_get_iter(emit_t *emit, bool use_stack) {
         emit_call(emit, MP_F_NATIVE_GETITER);
     } else {
         // mp_getiter will allocate the iter_buf on the heap
-        ASM_MOV_IMM_TO_REG(emit->as, 0, REG_ARG_2);
+        ASM_MOV_REG_IMM(emit->as, REG_ARG_2, 0);
         emit_call(emit, MP_F_NATIVE_GETITER);
         emit_post_push_reg(emit, VTYPE_PYOBJ, REG_RET);
     }
@@ -1784,7 +1737,7 @@ STATIC void emit_native_for_iter(emit_t *emit, mp_uint_t label) {
     emit_get_stack_pointer_to_reg_for_pop(emit, REG_ARG_1, MP_OBJ_ITER_BUF_NSLOTS);
     adjust_stack(emit, MP_OBJ_ITER_BUF_NSLOTS);
     emit_call(emit, MP_F_NATIVE_ITERNEXT);
-    ASM_MOV_IMM_TO_REG(emit->as, (mp_uint_t)MP_OBJ_STOP_ITERATION, REG_TEMP1);
+    ASM_MOV_REG_IMM(emit->as, REG_TEMP1, (mp_uint_t)MP_OBJ_STOP_ITERATION);
     ASM_JUMP_IF_REG_EQ(emit->as, REG_RET, REG_TEMP1, label);
     emit_post_push_reg(emit, VTYPE_PYOBJ, REG_RET);
 }
@@ -1998,26 +1951,29 @@ STATIC void emit_native_binary_op(emit_t *emit, mp_binary_op_t op) {
     }
 }
 
-STATIC void emit_native_build_tuple(emit_t *emit, mp_uint_t n_args) {
+#if MICROPY_PY_BUILTINS_SLICE
+STATIC void emit_native_build_slice(emit_t *emit, mp_uint_t n_args);
+#endif
+
+STATIC void emit_native_build(emit_t *emit, mp_uint_t n_args, int kind) {
     // for viper: call runtime, with types of args
     //   if wrapped in byte_array, or something, allocates memory and fills it
+    MP_STATIC_ASSERT(MP_F_BUILD_TUPLE + MP_EMIT_BUILD_TUPLE == MP_F_BUILD_TUPLE);
+    MP_STATIC_ASSERT(MP_F_BUILD_TUPLE + MP_EMIT_BUILD_LIST == MP_F_BUILD_LIST);
+    MP_STATIC_ASSERT(MP_F_BUILD_TUPLE + MP_EMIT_BUILD_MAP == MP_F_BUILD_MAP);
+    MP_STATIC_ASSERT(MP_F_BUILD_TUPLE + MP_EMIT_BUILD_SET == MP_F_BUILD_SET);
+    #if MICROPY_PY_BUILTINS_SLICE
+    if (kind == MP_EMIT_BUILD_SLICE) {
+        emit_native_build_slice(emit, n_args);
+        return;
+    }
+    #endif
     emit_native_pre(emit);
-    emit_get_stack_pointer_to_reg_for_pop(emit, REG_ARG_2, n_args); // pointer to items
-    emit_call_with_imm_arg(emit, MP_F_BUILD_TUPLE, n_args, REG_ARG_1);
-    emit_post_push_reg(emit, VTYPE_PYOBJ, REG_RET); // new tuple
-}
-
-STATIC void emit_native_build_list(emit_t *emit, mp_uint_t n_args) {
-    emit_native_pre(emit);
-    emit_get_stack_pointer_to_reg_for_pop(emit, REG_ARG_2, n_args); // pointer to items
-    emit_call_with_imm_arg(emit, MP_F_BUILD_LIST, n_args, REG_ARG_1);
-    emit_post_push_reg(emit, VTYPE_PYOBJ, REG_RET); // new list
-}
-
-STATIC void emit_native_build_map(emit_t *emit, mp_uint_t n_args) {
-    emit_native_pre(emit);
-    emit_call_with_imm_arg(emit, MP_F_BUILD_MAP, n_args, REG_ARG_1);
-    emit_post_push_reg(emit, VTYPE_PYOBJ, REG_RET); // new map
+    if (kind == MP_EMIT_BUILD_TUPLE || kind == MP_EMIT_BUILD_LIST || kind == MP_EMIT_BUILD_SET) {
+        emit_get_stack_pointer_to_reg_for_pop(emit, REG_ARG_2, n_args); // pointer to items
+    }
+    emit_call_with_imm_arg(emit, MP_F_BUILD_TUPLE + kind, n_args, REG_ARG_1);
+    emit_post_push_reg(emit, VTYPE_PYOBJ, REG_RET); // new tuple/list/map/set
 }
 
 STATIC void emit_native_store_map(emit_t *emit) {
@@ -2030,15 +1986,6 @@ STATIC void emit_native_store_map(emit_t *emit) {
     emit_post_push_reg(emit, VTYPE_PYOBJ, REG_RET); // map
 }
 
-#if MICROPY_PY_BUILTINS_SET
-STATIC void emit_native_build_set(emit_t *emit, mp_uint_t n_args) {
-    emit_native_pre(emit);
-    emit_get_stack_pointer_to_reg_for_pop(emit, REG_ARG_2, n_args); // pointer to items
-    emit_call_with_imm_arg(emit, MP_F_BUILD_SET, n_args, REG_ARG_1);
-    emit_post_push_reg(emit, VTYPE_PYOBJ, REG_RET); // new set
-}
-#endif
-
 #if MICROPY_PY_BUILTINS_SLICE
 STATIC void emit_native_build_slice(emit_t *emit, mp_uint_t n_args) {
     DEBUG_printf("build_slice %d\n", n_args);
@@ -2128,12 +2075,12 @@ STATIC void emit_native_make_closure(emit_t *emit, scope_t *scope, mp_uint_t n_c
     emit_native_pre(emit);
     if (n_pos_defaults == 0 && n_kw_defaults == 0) {
         emit_get_stack_pointer_to_reg_for_pop(emit, REG_ARG_3, n_closed_over);
-        ASM_MOV_IMM_TO_REG(emit->as, n_closed_over, REG_ARG_2);
+        ASM_MOV_REG_IMM(emit->as, REG_ARG_2, n_closed_over);
     } else {
         emit_get_stack_pointer_to_reg_for_pop(emit, REG_ARG_3, n_closed_over + 2);
-        ASM_MOV_IMM_TO_REG(emit->as, 0x100 | n_closed_over, REG_ARG_2);
+        ASM_MOV_REG_IMM(emit->as, REG_ARG_2, 0x100 | n_closed_over);
     }
-    ASM_MOV_ALIGNED_IMM_TO_REG(emit->as, (mp_uint_t)scope->raw_code, REG_ARG_1);
+    ASM_MOV_REG_ALIGNED_IMM(emit->as, REG_ARG_1, (mp_uint_t)scope->raw_code);
     ASM_CALL_IND(emit->as, mp_fun_table[MP_F_MAKE_CLOSURE_FROM_RAW_CODE], MP_F_MAKE_CLOSURE_FROM_RAW_CODE);
     emit_post_push_reg(emit, VTYPE_PYOBJ, REG_RET);
 }
@@ -2212,9 +2159,9 @@ STATIC void emit_native_return_value(emit_t *emit) {
         if (peek_vtype(emit, 0) == VTYPE_PTR_NONE) {
             emit_pre_pop_discard(emit);
             if (emit->return_vtype == VTYPE_PYOBJ) {
-                ASM_MOV_IMM_TO_REG(emit->as, (mp_uint_t)mp_const_none, REG_RET);
+                ASM_MOV_REG_IMM(emit->as, REG_RET, (mp_uint_t)mp_const_none);
             } else {
-                ASM_MOV_IMM_TO_REG(emit->as, 0, REG_RET);
+                ASM_MOV_REG_IMM(emit->as, REG_RET, 0);
             }
         } else {
             vtype_kind_t vtype;
@@ -2245,16 +2192,12 @@ STATIC void emit_native_raise_varargs(emit_t *emit, mp_uint_t n_args) {
     emit_call(emit, MP_F_NATIVE_RAISE);
 }
 
-STATIC void emit_native_yield_value(emit_t *emit) {
+STATIC void emit_native_yield(emit_t *emit, int kind) {
     // not supported (for now)
     (void)emit;
+    (void)kind;
     mp_raise_NotImplementedError("native yield");
 }
-STATIC void emit_native_yield_from(emit_t *emit) {
-    // not supported (for now)
-    (void)emit;
-    mp_raise_NotImplementedError("native yield from");
-}
 
 STATIC void emit_native_start_except_handler(emit_t *emit) {
     // This instruction follows an nlr_pop, so the stack counter is back to zero, when really
@@ -2280,41 +2223,29 @@ const emit_method_table_t EXPORT_FUN(method_table) = {
     emit_native_set_source_line,
 
     {
-        emit_native_load_fast,
-        emit_native_load_deref,
-        emit_native_load_name,
+        emit_native_load_local,
         emit_native_load_global,
     },
     {
-        emit_native_store_fast,
-        emit_native_store_deref,
-        emit_native_store_name,
+        emit_native_store_local,
         emit_native_store_global,
     },
     {
-        emit_native_delete_fast,
-        emit_native_delete_deref,
-        emit_native_delete_name,
+        emit_native_delete_local,
         emit_native_delete_global,
     },
 
     emit_native_label_assign,
-    emit_native_import_name,
-    emit_native_import_from,
-    emit_native_import_star,
+    emit_native_import,
     emit_native_load_const_tok,
     emit_native_load_const_small_int,
     emit_native_load_const_str,
     emit_native_load_const_obj,
     emit_native_load_null,
-    emit_native_load_attr,
     emit_native_load_method,
     emit_native_load_build_class,
-    emit_native_load_subscr,
-    emit_native_store_attr,
-    emit_native_store_subscr,
-    emit_native_delete_attr,
-    emit_native_delete_subscr,
+    emit_native_subscr,
+    emit_native_attr,
     emit_native_dup_top,
     emit_native_dup_top_two,
     emit_native_pop_top,
@@ -2323,12 +2254,9 @@ const emit_method_table_t EXPORT_FUN(method_table) = {
     emit_native_jump,
     emit_native_pop_jump_if,
     emit_native_jump_if_or_pop,
-    emit_native_break_loop,
-    emit_native_continue_loop,
-    emit_native_setup_with,
+    emit_native_unwind_jump,
+    emit_native_setup_block,
     emit_native_with_cleanup,
-    emit_native_setup_except,
-    emit_native_setup_finally,
     emit_native_end_finally,
     emit_native_get_iter,
     emit_native_for_iter,
@@ -2337,16 +2265,8 @@ const emit_method_table_t EXPORT_FUN(method_table) = {
     emit_native_pop_except,
     emit_native_unary_op,
     emit_native_binary_op,
-    emit_native_build_tuple,
-    emit_native_build_list,
-    emit_native_build_map,
+    emit_native_build,
     emit_native_store_map,
-    #if MICROPY_PY_BUILTINS_SET
-    emit_native_build_set,
-    #endif
-    #if MICROPY_PY_BUILTINS_SLICE
-    emit_native_build_slice,
-    #endif
     emit_native_store_comp,
     emit_native_unpack_sequence,
     emit_native_unpack_ex,
@@ -2356,8 +2276,7 @@ const emit_method_table_t EXPORT_FUN(method_table) = {
     emit_native_call_method,
     emit_native_return_value,
     emit_native_raise_varargs,
-    emit_native_yield_value,
-    emit_native_yield_from,
+    emit_native_yield,
 
     emit_native_start_except_handler,
     emit_native_end_except_handler,
diff --git a/py/emitnthumb.c b/py/emitnthumb.c
new file mode 100644
index 000000000..2b68ca3a1
--- /dev/null
+++ b/py/emitnthumb.c
@@ -0,0 +1,15 @@
+// thumb specific stuff
+
+#include "py/mpconfig.h"
+
+#if MICROPY_EMIT_THUMB
+
+// this is defined so that the assembler exports generic assembler API macros
+#define GENERIC_ASM_API (1)
+#include "py/asmthumb.h"
+
+#define N_THUMB (1)
+#define EXPORT_FUN(name) emit_native_thumb_##name
+#include "py/emitnative.c"
+
+#endif
diff --git a/py/emitnx64.c b/py/emitnx64.c
new file mode 100644
index 000000000..b9800f636
--- /dev/null
+++ b/py/emitnx64.c
@@ -0,0 +1,15 @@
+// x64 specific stuff
+
+#include "py/mpconfig.h"
+
+#if MICROPY_EMIT_X64
+
+// This is defined so that the assembler exports generic assembler API macros
+#define GENERIC_ASM_API (1)
+#include "py/asmx64.h"
+
+#define N_X64 (1)
+#define EXPORT_FUN(name) emit_native_x64_##name
+#include "py/emitnative.c"
+
+#endif
diff --git a/py/emitnx86.c b/py/emitnx86.c
new file mode 100644
index 000000000..5d2bbb267
--- /dev/null
+++ b/py/emitnx86.c
@@ -0,0 +1,68 @@
+// x86 specific stuff
+
+#include "py/mpconfig.h"
+#include "py/runtime0.h"
+
+#if MICROPY_EMIT_X86
+
+// This is defined so that the assembler exports generic assembler API macros
+#define GENERIC_ASM_API (1)
+#include "py/asmx86.h"
+
+// x86 needs a table to know how many args a given function has
+STATIC byte mp_f_n_args[MP_F_NUMBER_OF] = {
+    [MP_F_CONVERT_OBJ_TO_NATIVE] = 2,
+    [MP_F_CONVERT_NATIVE_TO_OBJ] = 2,
+    [MP_F_LOAD_NAME] = 1,
+    [MP_F_LOAD_GLOBAL] = 1,
+    [MP_F_LOAD_BUILD_CLASS] = 0,
+    [MP_F_LOAD_ATTR] = 2,
+    [MP_F_LOAD_METHOD] = 3,
+    [MP_F_LOAD_SUPER_METHOD] = 2,
+    [MP_F_STORE_NAME] = 2,
+    [MP_F_STORE_GLOBAL] = 2,
+    [MP_F_STORE_ATTR] = 3,
+    [MP_F_OBJ_SUBSCR] = 3,
+    [MP_F_OBJ_IS_TRUE] = 1,
+    [MP_F_UNARY_OP] = 2,
+    [MP_F_BINARY_OP] = 3,
+    [MP_F_BUILD_TUPLE] = 2,
+    [MP_F_BUILD_LIST] = 2,
+    [MP_F_LIST_APPEND] = 2,
+    [MP_F_BUILD_MAP] = 1,
+    [MP_F_STORE_MAP] = 3,
+    #if MICROPY_PY_BUILTINS_SET
+    [MP_F_BUILD_SET] = 2,
+    [MP_F_STORE_SET] = 2,
+    #endif
+    [MP_F_MAKE_FUNCTION_FROM_RAW_CODE] = 3,
+    [MP_F_NATIVE_CALL_FUNCTION_N_KW] = 3,
+    [MP_F_CALL_METHOD_N_KW] = 3,
+    [MP_F_CALL_METHOD_N_KW_VAR] = 3,
+    [MP_F_NATIVE_GETITER] = 2,
+    [MP_F_NATIVE_ITERNEXT] = 1,
+    [MP_F_NLR_PUSH] = 1,
+    [MP_F_NLR_POP] = 0,
+    [MP_F_NATIVE_RAISE] = 1,
+    [MP_F_IMPORT_NAME] = 3,
+    [MP_F_IMPORT_FROM] = 2,
+    [MP_F_IMPORT_ALL] = 1,
+    #if MICROPY_PY_BUILTINS_SLICE
+    [MP_F_NEW_SLICE] = 3,
+    #endif
+    [MP_F_UNPACK_SEQUENCE] = 3,
+    [MP_F_UNPACK_EX] = 3,
+    [MP_F_DELETE_NAME] = 1,
+    [MP_F_DELETE_GLOBAL] = 1,
+    [MP_F_NEW_CELL] = 1,
+    [MP_F_MAKE_CLOSURE_FROM_RAW_CODE] = 3,
+    [MP_F_SETUP_CODE_STATE] = 5,
+    [MP_F_SMALL_INT_FLOOR_DIVIDE] = 2,
+    [MP_F_SMALL_INT_MODULO] = 2,
+};
+
+#define N_X86 (1)
+#define EXPORT_FUN(name) emit_native_x86_##name
+#include "py/emitnative.c"
+
+#endif
diff --git a/py/emitnxtensa.c b/py/emitnxtensa.c
new file mode 100644
index 000000000..1a423e21e
--- /dev/null
+++ b/py/emitnxtensa.c
@@ -0,0 +1,15 @@
+// Xtensa specific stuff
+
+#include "py/mpconfig.h"
+
+#if MICROPY_EMIT_XTENSA
+
+// this is defined so that the assembler exports generic assembler API macros
+#define GENERIC_ASM_API (1)
+#include "py/asmxtensa.h"
+
+#define N_XTENSA (1)
+#define EXPORT_FUN(name) emit_native_xtensa_##name
+#include "py/emitnative.c"
+
+#endif
diff --git a/py/formatfloat.c b/py/formatfloat.c
index 4228f99ff..dc7fc1d1f 100644
--- a/py/formatfloat.c
+++ b/py/formatfloat.c
@@ -258,7 +258,7 @@ int mp_format_float(FPTYPE f, char *buf, size_t buf_size, char fmt, int prec, ch
         }
 
         // It can be that f was right on the edge of an entry in pos_pow needs to be reduced
-        if (f >= FPCONST(10.0)) {
+        if ((int)f >= 10) {
             e += 1;
             f *= FPCONST(0.1);
         }
@@ -330,7 +330,11 @@ int mp_format_float(FPTYPE f, char *buf, size_t buf_size, char fmt, int prec, ch
     // Print the digits of the mantissa
     for (int i = 0; i < num_digits; ++i, --dec) {
         int32_t d = (int32_t)f;
-        *s++ = '0' + d;
+        if (d < 0) {
+            *s++ = '0';
+        } else {
+            *s++ = '0' + d;
+        }
         if (dec == 0 && prec > 0) {
             *s++ = '.';
         }
@@ -341,7 +345,7 @@ int mp_format_float(FPTYPE f, char *buf, size_t buf_size, char fmt, int prec, ch
     // Round
     // If we print non-exponential format (i.e. 'f'), but a digit we're going
     // to round by (e) is too far away, then there's nothing to round.
-    if ((org_fmt != 'f' || e <= 1) && f >= FPCONST(5.0)) {
+    if ((org_fmt != 'f' || e <= num_digits) && f >= FPCONST(5.0)) {
         char *rs = s;
         rs--;
         while (1) {
diff --git a/py/gc.c b/py/gc.c
index 2c2354e4c..1f5cd8d01 100755
--- a/py/gc.c
+++ b/py/gc.c
@@ -47,6 +47,10 @@
 // make this 1 to dump the heap each time it changes
 #define EXTENSIVE_HEAP_PROFILING (0)
 
+// make this 1 to zero out swept memory to more eagerly
+// detect untraced object still in use
+#define CLEAR_ON_SWEEP (0)
+
 #define WORDS_PER_BLOCK ((MICROPY_BYTES_PER_GC_BLOCK) / BYTES_PER_WORD)
 #define BYTES_PER_BLOCK (MICROPY_BYTES_PER_GC_BLOCK)
 
@@ -201,29 +205,22 @@ bool gc_is_locked(void) {
         && ptr < (void*)MP_STATE_MEM(gc_pool_end)        /* must be below end of pool */ \
     )
 
-// ptr should be of type void*
-#define VERIFY_MARK_AND_PUSH(ptr) \
-    do { \
-        if (VERIFY_PTR(ptr)) { \
-            size_t _block = BLOCK_FROM_PTR(ptr); \
-            if (ATB_GET_KIND(_block) == AT_HEAD) { \
-                /* an unmarked head, mark it, and push it on gc stack */ \
-                DEBUG_printf("gc_mark(%p)\n", ptr); \
-                ATB_HEAD_TO_MARK(_block); \
-                if (MP_STATE_MEM(gc_sp) < &MP_STATE_MEM(gc_stack)[MICROPY_ALLOC_GC_STACK_SIZE]) { \
-                    *MP_STATE_MEM(gc_sp)++ = _block; \
-                } else { \
-                    MP_STATE_MEM(gc_stack_overflow) = 1; \
-                } \
-            } \
-        } \
-    } while (0)
-
-STATIC void gc_drain_stack(void) {
-    while (MP_STATE_MEM(gc_sp) > MP_STATE_MEM(gc_stack)) {
-        // pop the next block off the stack
-        size_t block = *--MP_STATE_MEM(gc_sp);
+#ifndef TRACE_MARK
+#if DEBUG_PRINT
+#define TRACE_MARK(block, ptr) DEBUG_printf("gc_mark(%p)\n", ptr)
+#else
+#define TRACE_MARK(block, ptr)
+#endif
+#endif
 
+// Take the given block as the topmost block on the stack. Check all it's
+// children: mark the unmarked child blocks and put those newly marked
+// blocks on the stack. When all children have been checked, pop off the
+// topmost block on the stack and repeat with that one.
+STATIC void gc_mark_subtree(size_t block) {
+    // Start with the block passed in the argument.
+    size_t sp = 0;
+    for (;;) {
         // work out number of consecutive blocks in the chain starting with this one
         size_t n_blocks = 0;
         do {
@@ -234,22 +231,41 @@ STATIC void gc_drain_stack(void) {
         void **ptrs = (void**)PTR_FROM_BLOCK(block);
         for (size_t i = n_blocks * BYTES_PER_BLOCK / sizeof(void*); i > 0; i--, ptrs++) {
             void *ptr = *ptrs;
-            VERIFY_MARK_AND_PUSH(ptr);
+            if (VERIFY_PTR(ptr)) {
+                // Mark and push this pointer
+                size_t childblock = BLOCK_FROM_PTR(ptr);
+                if (ATB_GET_KIND(childblock) == AT_HEAD) {
+                    // an unmarked head, mark it, and push it on gc stack
+                    TRACE_MARK(childblock, ptr);
+                    ATB_HEAD_TO_MARK(childblock);
+                    if (sp < MICROPY_ALLOC_GC_STACK_SIZE) {
+                        MP_STATE_MEM(gc_stack)[sp++] = childblock;
+                    } else {
+                        MP_STATE_MEM(gc_stack_overflow) = 1;
+                    }
+                }
+            }
         }
+
+        // Are there any blocks on the stack?
+        if (sp == 0) {
+            break; // No, stack is empty, we're done.
+        }
+
+        // pop the next block off the stack
+        block = MP_STATE_MEM(gc_stack)[--sp];
     }
 }
 
 STATIC void gc_deal_with_stack_overflow(void) {
     while (MP_STATE_MEM(gc_stack_overflow)) {
         MP_STATE_MEM(gc_stack_overflow) = 0;
-        MP_STATE_MEM(gc_sp) = MP_STATE_MEM(gc_stack);
 
         // scan entire memory looking for blocks which have been marked but not their children
         for (size_t block = 0; block < MP_STATE_MEM(gc_alloc_table_byte_len) * BLOCKS_PER_ATB; block++) {
             // trace (again) if mark bit set
             if (ATB_GET_KIND(block) == AT_MARK) {
-                *MP_STATE_MEM(gc_sp)++ = block;
-                gc_drain_stack();
+                gc_mark_subtree(block);
             }
         }
     }
@@ -288,6 +304,9 @@ STATIC void gc_sweep(void) {
 #endif
                 free_tail = 1;
                 ATB_ANY_TO_FREE(block);
+                #if CLEAR_ON_SWEEP
+                memset((void*)PTR_FROM_BLOCK(block), 0, BYTES_PER_BLOCK);
+                #endif
                 DEBUG_printf("gc_sweep(%x)\n", PTR_FROM_BLOCK(block));
 
                 #ifdef LOG_HEAP_ACTIVITY
@@ -301,6 +320,9 @@ STATIC void gc_sweep(void) {
             case AT_TAIL:
                 if (free_tail) {
                     ATB_ANY_TO_FREE(block);
+                    #if CLEAR_ON_SWEEP
+                    memset((void*)PTR_FROM_BLOCK(block), 0, BYTES_PER_BLOCK);
+                    #endif
                 }
                 break;
 
@@ -319,19 +341,34 @@ void gc_collect_start(void) {
     MP_STATE_MEM(gc_alloc_amount) = 0;
     #endif
     MP_STATE_MEM(gc_stack_overflow) = 0;
-    MP_STATE_MEM(gc_sp) = MP_STATE_MEM(gc_stack);
+
     // Trace root pointers.  This relies on the root pointers being organised
     // correctly in the mp_state_ctx structure.  We scan nlr_top, dict_locals,
     // dict_globals, then the root pointer section of mp_state_vm.
     void **ptrs = (void**)(void*)&mp_state_ctx;
-    gc_collect_root(ptrs, offsetof(mp_state_ctx_t, vm.qstr_last_chunk) / sizeof(void*));
+    size_t root_start = offsetof(mp_state_ctx_t, thread.dict_locals);
+    size_t root_end = offsetof(mp_state_ctx_t, vm.qstr_last_chunk);
+    gc_collect_root(ptrs + root_start / sizeof(void*), (root_end - root_start) / sizeof(void*));
+
+    #if MICROPY_ENABLE_PYSTACK
+    // Trace root pointers from the Python stack.
+    ptrs = (void**)(void*)MP_STATE_THREAD(pystack_start);
+    gc_collect_root(ptrs, (MP_STATE_THREAD(pystack_cur) - MP_STATE_THREAD(pystack_start)) / sizeof(void*));
+    #endif
 }
 
 void gc_collect_root(void **ptrs, size_t len) {
     for (size_t i = 0; i < len; i++) {
         void *ptr = ptrs[i];
-        VERIFY_MARK_AND_PUSH(ptr);
-        gc_drain_stack();
+        if (VERIFY_PTR(ptr)) {
+            size_t block = BLOCK_FROM_PTR(ptr);
+            if (ATB_GET_KIND(block) == AT_HEAD) {
+                // An unmarked head: mark it, and mark all its children
+                TRACE_MARK(block, ptr);
+                ATB_HEAD_TO_MARK(block);
+                gc_mark_subtree(block);
+            }
+        }
     }
 }
 
@@ -344,6 +381,13 @@ void gc_collect_end(void) {
     GC_EXIT();
 }
 
+void gc_sweep_all(void) {
+    GC_ENTER();
+    MP_STATE_MEM(gc_lock_depth)++;
+    MP_STATE_MEM(gc_stack_overflow) = 0;
+    gc_collect_end();
+}
+
 void gc_info(gc_info_t *info) {
     GC_ENTER();
     info->total = MP_STATE_MEM(gc_pool_end) - MP_STATE_MEM(gc_pool_start);
@@ -437,6 +481,7 @@ void *gc_alloc(size_t n_bytes, bool has_finaliser, bool long_lived) {
     if (!collected && MP_STATE_MEM(gc_alloc_amount) >= MP_STATE_MEM(gc_alloc_threshold)) {
         GC_EXIT();
         gc_collect();
+        collected = 1;
         GC_ENTER();
         collected = true;
     }
@@ -748,27 +793,18 @@ void *gc_realloc(void *ptr_in, size_t n_bytes, bool allow_move) {
 
     void *ptr = ptr_in;
 
-    // sanity check the ptr
-    if (!VERIFY_PTR(ptr)) {
-        return NULL;
-    }
-
-    // get first block
-    size_t block = BLOCK_FROM_PTR(ptr);
-
     GC_ENTER();
 
-    // sanity check the ptr is pointing to the head of a block
-    if (ATB_GET_KIND(block) != AT_HEAD) {
-        GC_EXIT();
-        return NULL;
-    }
-
     if (MP_STATE_MEM(gc_lock_depth) > 0) {
         GC_EXIT();
         return NULL;
     }
 
+    // get the GC block number corresponding to this pointer
+    assert(VERIFY_PTR(ptr));
+    size_t block = BLOCK_FROM_PTR(ptr);
+    assert(ATB_GET_KIND(block) == AT_HEAD);
+
     // compute number of new blocks that are requested
     size_t new_blocks = (n_bytes + BYTES_PER_BLOCK - 1) / BYTES_PER_BLOCK;
 
diff --git a/py/gc.h b/py/gc.h
index e5878e1ee..64f4b0d17 100644
--- a/py/gc.h
+++ b/py/gc.h
@@ -46,6 +46,10 @@ void gc_collect_root(void **ptrs, size_t len);
 void gc_collect_end(void);
 
 void *gc_alloc(size_t n_bytes, bool has_finaliser, bool long_lived);
+
+// Use this function to sweep the whole heap and run all finalisers
+void gc_sweep_all(void);
+
 void gc_free(void *ptr); // does not call finaliser
 size_t gc_nbytes(const void *ptr);
 bool gc_has_finaliser(const void *ptr);
diff --git a/py/grammar.h b/py/grammar.h
index 6abb1de8c..5a5b682ac 100644
--- a/py/grammar.h
+++ b/py/grammar.h
@@ -122,8 +122,8 @@ DEF_RULE_NC(augassign, or(12), tok(DEL_PLUS_EQUAL), tok(DEL_MINUS_EQUAL), tok(DE
 DEF_RULE(del_stmt, c(del_stmt), and(2), tok(KW_DEL), rule(exprlist))
 DEF_RULE(pass_stmt, c(generic_all_nodes), and(1), tok(KW_PASS))
 DEF_RULE_NC(flow_stmt, or(5), rule(break_stmt), rule(continue_stmt), rule(return_stmt), rule(raise_stmt), rule(yield_stmt))
-DEF_RULE(break_stmt, c(break_stmt), and(1), tok(KW_BREAK))
-DEF_RULE(continue_stmt, c(continue_stmt), and(1), tok(KW_CONTINUE))
+DEF_RULE(break_stmt, c(break_cont_stmt), and(1), tok(KW_BREAK))
+DEF_RULE(continue_stmt, c(break_cont_stmt), and(1), tok(KW_CONTINUE))
 DEF_RULE(return_stmt, c(return_stmt), and(2), tok(KW_RETURN), opt_rule(testlist))
 DEF_RULE(yield_stmt, c(yield_stmt), and(1), rule(yield_expr))
 DEF_RULE(raise_stmt, c(raise_stmt), and(2), tok(KW_RAISE), opt_rule(raise_stmt_arg))
@@ -157,8 +157,8 @@ DEF_RULE_NC(as_name, and_ident(2), tok(KW_AS), tok(NAME))
 DEF_RULE_NC(import_as_names, list_with_end, rule(import_as_name), tok(DEL_COMMA))
 DEF_RULE_NC(dotted_as_names, list, rule(dotted_as_name), tok(DEL_COMMA))
 DEF_RULE_NC(dotted_name, list, tok(NAME), tok(DEL_PERIOD))
-DEF_RULE(global_stmt, c(global_stmt), and(2), tok(KW_GLOBAL), rule(name_list))
-DEF_RULE(nonlocal_stmt, c(nonlocal_stmt), and(2), tok(KW_NONLOCAL), rule(name_list))
+DEF_RULE(global_stmt, c(global_nonlocal_stmt), and(2), tok(KW_GLOBAL), rule(name_list))
+DEF_RULE(nonlocal_stmt, c(global_nonlocal_stmt), and(2), tok(KW_NONLOCAL), rule(name_list))
 DEF_RULE_NC(name_list, list, tok(NAME), tok(DEL_COMMA))
 DEF_RULE(assert_stmt, c(assert_stmt), and(3), tok(KW_ASSERT), rule(test), opt_rule(assert_stmt_extra))
 DEF_RULE_NC(assert_stmt_extra, and_ident(2), tok(DEL_COMMA), rule(test))
@@ -231,8 +231,8 @@ DEF_RULE(lambdef_nocond, c(lambdef), and_blank(4), tok(KW_LAMBDA), opt_rule(vara
 // power: atom_expr ['**' factor]
 // atom_expr: 'await' atom trailer* | atom trailer*
 
-DEF_RULE(or_test, c(or_test), list, rule(and_test), tok(KW_OR))
-DEF_RULE(and_test, c(and_test), list, rule(not_test), tok(KW_AND))
+DEF_RULE(or_test, c(or_and_test), list, rule(and_test), tok(KW_OR))
+DEF_RULE(and_test, c(or_and_test), list, rule(not_test), tok(KW_AND))
 DEF_RULE_NC(not_test, or(2), rule(not_test_2), rule(comparison))
 DEF_RULE(not_test_2, c(not_test_2), and(2), tok(KW_NOT), rule(not_test))
 DEF_RULE(comparison, c(comparison), list, rule(expr), rule(comp_op))
@@ -241,9 +241,9 @@ DEF_RULE_NC(comp_op_not_in, and(2), tok(KW_NOT), tok(KW_IN))
 DEF_RULE_NC(comp_op_is, and(2), tok(KW_IS), opt_rule(comp_op_is_not))
 DEF_RULE_NC(comp_op_is_not, and(1), tok(KW_NOT))
 DEF_RULE(star_expr, c(star_expr), and(2), tok(OP_STAR), rule(expr))
-DEF_RULE(expr, c(expr), list, rule(xor_expr), tok(OP_PIPE))
-DEF_RULE(xor_expr, c(xor_expr), list, rule(and_expr), tok(OP_CARET))
-DEF_RULE(and_expr, c(and_expr), list, rule(shift_expr), tok(OP_AMPERSAND))
+DEF_RULE(expr, c(binary_op), list, rule(xor_expr), tok(OP_PIPE))
+DEF_RULE(xor_expr, c(binary_op), list, rule(and_expr), tok(OP_CARET))
+DEF_RULE(and_expr, c(binary_op), list, rule(shift_expr), tok(OP_AMPERSAND))
 DEF_RULE(shift_expr, c(term), list, rule(arith_expr), rule(shift_op))
 DEF_RULE_NC(shift_op, or(2), tok(OP_DBL_LESS), tok(OP_DBL_MORE))
 DEF_RULE(arith_expr, c(term), list, rule(term), rule(arith_op))
@@ -290,8 +290,8 @@ DEF_RULE(trailer_period, c(trailer_period), and(2), tok(DEL_PERIOD), tok(NAME))
 #if MICROPY_PY_BUILTINS_SLICE
 DEF_RULE(subscriptlist, c(generic_tuple), list_with_end, rule(subscript), tok(DEL_COMMA))
 DEF_RULE_NC(subscript, or(2), rule(subscript_3), rule(subscript_2))
-DEF_RULE(subscript_2, c(subscript_2), and_ident(2), rule(test), opt_rule(subscript_3))
-DEF_RULE(subscript_3, c(subscript_3), and(2), tok(DEL_COLON), opt_rule(subscript_3b))
+DEF_RULE(subscript_2, c(subscript), and_ident(2), rule(test), opt_rule(subscript_3))
+DEF_RULE(subscript_3, c(subscript), and(2), tok(DEL_COLON), opt_rule(subscript_3b))
 DEF_RULE_NC(subscript_3b, or(2), rule(subscript_3c), rule(subscript_3d))
 DEF_RULE_NC(subscript_3c, and(2), tok(DEL_COLON), opt_rule(test))
 DEF_RULE_NC(subscript_3d, and_ident(2), rule(test), opt_rule(sliceop))
diff --git a/py/lexer.c b/py/lexer.c
index 6017d69d6..e161700b1 100644
--- a/py/lexer.c
+++ b/py/lexer.c
@@ -590,6 +590,8 @@ void mp_lexer_to_next(mp_lexer_t *lex) {
                 }
                 vstr_add_char(&lex->vstr, CUR_CHAR(lex));
                 next_char(lex);
+            } else if (is_char(lex, '_')) {
+                next_char(lex);
             } else {
                 break;
             }
diff --git a/py/makeqstrdata.py b/py/makeqstrdata.py
index 38fde1a9c..3c0a60909 100644
--- a/py/makeqstrdata.py
+++ b/py/makeqstrdata.py
@@ -114,6 +114,9 @@ def parse_input_headers(infiles):
                 if ident == "":
                     # Sort empty qstr above all still
                     order = -200000
+                elif ident == "__dir__":
+                    # Put __dir__ after empty qstr for builtin dir() to work
+                    order = -190000
                 elif ident.startswith("__"):
                     order -= 100000
                 qstrs[ident] = (order, ident, qstr)
diff --git a/py/makeqstrdefs.py b/py/makeqstrdefs.py
index 0a45c585a..4253c1147 100644
--- a/py/makeqstrdefs.py
+++ b/py/makeqstrdefs.py
@@ -73,12 +73,16 @@ def qstr_unescape(qstr):
     return qstr
 
 def process_file(f):
+    re_line = re.compile(r"#[line]*\s\d+\s\"([^\"]+)\"")
+    re_qstr = re.compile(r'MP_QSTR_[_a-zA-Z0-9]+')
     output = []
     last_fname = None
     for line in f:
+        if line.isspace():
+            continue
         # match gcc-like output (# n "file") and msvc-like output (#line n "file")
-        if line and (line[0:2] == "# " or line[0:5] == "#line"):
-            m = re.match(r"#[line]*\s\d+\s\"([^\"]+)\"", line)
+        if line.startswith(('# ', '#line')):
+            m = re_line.match(line)
             assert m is not None
             fname = m.group(1)
             if not fname.endswith(".c"):
@@ -88,7 +92,7 @@ def process_file(f):
                 output = []
                 last_fname = fname
             continue
-        for match in re.findall(r'MP_QSTR_[_a-zA-Z0-9]+', line):
+        for match in re_qstr.findall(line):
             name = match.replace('MP_QSTR_', '')
             if name not in QSTRING_BLACK_LIST:
                 output.append('Q(' + qstr_unescape(name) + ')')
diff --git a/py/makeversionhdr.py b/py/makeversionhdr.py
index 1f82d5933..89a604aeb 100644
--- a/py/makeversionhdr.py
+++ b/py/makeversionhdr.py
@@ -100,7 +100,7 @@ def make_version_header(filename):
 
     # Only write the file if we need to
     if write_file:
-        print("Generating %s" % filename)
+        print("GEN %s" % filename)
         with open(filename, 'w') as f:
             f.write(file_data)
 
diff --git a/py/malloc.c b/py/malloc.c
index d6983ffdf..f190582ab 100644
--- a/py/malloc.c
+++ b/py/malloc.c
@@ -39,6 +39,9 @@
 #endif
 
 #if MICROPY_MEM_STATS
+#if !MICROPY_MALLOC_USES_ALLOCATED_SIZE
+#error MICROPY_MEM_STATS requires MICROPY_MALLOC_USES_ALLOCATED_SIZE
+#endif
 #define UPDATE_PEAK() { if (MP_STATE_MEM(current_bytes_allocated) > MP_STATE_MEM(peak_bytes_allocated)) MP_STATE_MEM(peak_bytes_allocated) = MP_STATE_MEM(current_bytes_allocated); }
 #endif
 
@@ -117,9 +120,6 @@ void *m_malloc_with_finaliser(size_t num_bytes) {
 
 void *m_malloc0(size_t num_bytes, bool long_lived) {
     void *ptr = m_malloc(num_bytes, long_lived);
-    if (ptr == NULL && num_bytes != 0) {
-        m_malloc_fail(num_bytes);
-    }
     // If this config is set then the GC clears all memory, so we don't need to.
     #if !MICROPY_GC_CONSERVATIVE_CLEAR
     memset(ptr, 0, num_bytes);
@@ -147,7 +147,11 @@ void *m_realloc(void *ptr, size_t new_num_bytes) {
     MP_STATE_MEM(current_bytes_allocated) += diff;
     UPDATE_PEAK();
 #endif
+    #if MICROPY_MALLOC_USES_ALLOCATED_SIZE
     DEBUG_printf("realloc %p, %d, %d : %p\n", ptr, old_num_bytes, new_num_bytes, new_ptr);
+    #else
+    DEBUG_printf("realloc %p, %d : %p\n", ptr, new_num_bytes, new_ptr);
+    #endif
     return new_ptr;
 }
 
@@ -171,7 +175,11 @@ void *m_realloc_maybe(void *ptr, size_t new_num_bytes, bool allow_move) {
         UPDATE_PEAK();
     }
 #endif
+    #if MICROPY_MALLOC_USES_ALLOCATED_SIZE
     DEBUG_printf("realloc %p, %d, %d : %p\n", ptr, old_num_bytes, new_num_bytes, new_ptr);
+    #else
+    DEBUG_printf("realloc %p, %d, %d : %p\n", ptr, new_num_bytes, new_ptr);
+    #endif
     return new_ptr;
 }
 
@@ -184,7 +192,11 @@ void m_free(void *ptr) {
 #if MICROPY_MEM_STATS
     MP_STATE_MEM(current_bytes_allocated) -= num_bytes;
 #endif
+    #if MICROPY_MALLOC_USES_ALLOCATED_SIZE
     DEBUG_printf("free %p, %d\n", ptr, num_bytes);
+    #else
+    DEBUG_printf("free %p\n", ptr);
+    #endif
 }
 
 #if MICROPY_MEM_STATS
diff --git a/py/map.c b/py/map.c
index 4f76b9b16..6abf4853f 100644
--- a/py/map.c
+++ b/py/map.c
@@ -33,6 +33,13 @@
 #include "py/misc.h"
 #include "py/runtime.h"
 
+#if MICROPY_DEBUG_VERBOSE // print debugging info
+#define DEBUG_PRINT (1)
+#else // don't print debugging info
+#define DEBUG_PRINT (0)
+#define DEBUG_printf(...) (void)0
+#endif
+
 // Fixed empty map. Useful when need to call kw-receiving functions
 // without any keywords from C, etc.
 const mp_map_t mp_const_empty_map = {
@@ -114,6 +121,7 @@ void mp_map_clear(mp_map_t *map) {
 STATIC void mp_map_rehash(mp_map_t *map) {
     size_t old_alloc = map->alloc;
     size_t new_alloc = get_hash_alloc_greater_or_equal_to(map->alloc + 1);
+    DEBUG_printf("mp_map_rehash(%p): " UINT_FMT " -> " UINT_FMT "\n", map, old_alloc, new_alloc);
     mp_map_elem_t *old_table = map->table;
     mp_map_elem_t *new_table = m_new0(mp_map_elem_t, new_alloc);
     // If we reach this point, table resizing succeeded, now we can edit the old map.
@@ -162,6 +170,7 @@ mp_map_elem_t *mp_map_lookup(mp_map_t *map, mp_obj_t index, mp_map_lookup_kind_t
     if (map->is_ordered) {
         for (mp_map_elem_t *elem = &map->table[0], *top = &map->table[map->used]; elem < top; elem++) {
             if (elem->key == index || (!compare_only_ptrs && mp_obj_equal(elem->key, index))) {
+                #if MICROPY_PY_COLLECTIONS_ORDEREDDICT
                 if (MP_UNLIKELY(lookup_kind == MP_MAP_LOOKUP_REMOVE_IF_FOUND)) {
                     // remove the found element by moving the rest of the array down
                     mp_obj_t value = elem->value;
@@ -172,9 +181,11 @@ mp_map_elem_t *mp_map_lookup(mp_map_t *map, mp_obj_t index, mp_map_lookup_kind_t
                     elem->key = MP_OBJ_NULL;
                     elem->value = value;
                 }
+                #endif
                 return elem;
             }
         }
+        #if MICROPY_PY_COLLECTIONS_ORDEREDDICT
         if (MP_LIKELY(lookup_kind != MP_MAP_LOOKUP_ADD_IF_NOT_FOUND)) {
             return NULL;
         }
@@ -190,6 +201,9 @@ mp_map_elem_t *mp_map_lookup(mp_map_t *map, mp_obj_t index, mp_map_lookup_kind_t
             map->all_keys_are_qstrs = 0;
         }
         return elem;
+        #else
+        return NULL;
+        #endif
     }
 
     // map is a hash table (not an ordered array), so do a hash lookup
diff --git a/py/misc.h b/py/misc.h
index d9a8efe7f..673568f22 100644
--- a/py/misc.h
+++ b/py/misc.h
@@ -52,6 +52,9 @@ typedef unsigned int uint;
 #define _MP_STRINGIFY(x) #x
 #define MP_STRINGIFY(x) _MP_STRINGIFY(x)
 
+// Static assertion macro
+#define MP_STATIC_ASSERT(cond) ((void)sizeof(char[1 - 2 * !(cond)]))
+
 /** memory allocation ******************************************/
 
 // TODO make a lazy m_renew that can increase by a smaller amount than requested (but by at least 1 more element)
@@ -70,8 +73,10 @@ typedef unsigned int uint;
 #define m_new_ll_obj_var_maybe(obj_type, var_type, var_num) ((obj_type*)m_malloc_maybe(sizeof(obj_type) + sizeof(var_type) * (var_num), true))
 #if MICROPY_ENABLE_FINALISER
 #define m_new_obj_with_finaliser(type) ((type*)(m_malloc_with_finaliser(sizeof(type))))
+#define m_new_obj_var_with_finaliser(type, var_type, var_num) ((type*)m_malloc_with_finaliser(sizeof(type) + sizeof(var_type) * (var_num)))
 #else
 #define m_new_obj_with_finaliser(type) m_new_obj(type)
+#define m_new_obj_var_with_finaliser(type, var_type, var_num) m_new_obj_var(type, var_type, var_num)
 #endif
 #if MICROPY_MALLOC_USES_ALLOCATED_SIZE
 #define m_renew(type, ptr, old_num, new_num) ((type*)(m_realloc((ptr), sizeof(type) * (old_num), sizeof(type) * (new_num))))
@@ -126,8 +131,15 @@ typedef uint32_t unichar;
 typedef uint unichar;
 #endif
 
+#if MICROPY_PY_BUILTINS_STR_UNICODE
 unichar utf8_get_char(const byte *s);
 const byte *utf8_next_char(const byte *s);
+size_t utf8_charlen(const byte *str, size_t len);
+#else
+static inline unichar utf8_get_char(const byte *s) { return *s; }
+static inline const byte *utf8_next_char(const byte *s) { return s + 1; }
+static inline size_t utf8_charlen(const byte *str, size_t len) { (void)str; return len; }
+#endif
 
 bool unichar_isspace(unichar c);
 bool unichar_isalpha(unichar c);
@@ -140,7 +152,6 @@ bool unichar_islower(unichar c);
 unichar unichar_tolower(unichar c);
 unichar unichar_toupper(unichar c);
 mp_uint_t unichar_xdigit_value(unichar c);
-mp_uint_t unichar_charlen(const char *str, mp_uint_t len);
 #define UTF8_IS_NONASCII(ch) ((ch) & 0x80)
 #define UTF8_IS_CONT(ch) (((ch) & 0xC0) == 0x80)
 
@@ -203,20 +214,6 @@ int DEBUG_printf(const char *fmt, ...);
 
 extern mp_uint_t mp_verbose_flag;
 
-// This is useful for unicode handling. Some CPU archs has
-// special instructions for efficient implementation of this
-// function (e.g. CLZ on ARM).
-// NOTE: this function is unused at the moment
-#ifndef count_lead_ones
-static inline mp_uint_t count_lead_ones(byte val) {
-    mp_uint_t c = 0;
-    for (byte mask = 0x80; val & mask; mask >>= 1) {
-        c++;
-    }
-    return c;
-}
-#endif
-
 /** float internals *************/
 
 #if MICROPY_PY_BUILTINS_FLOAT
diff --git a/py/mkenv.mk b/py/mkenv.mk
index 5f8cd902b..1b316c39d 100644
--- a/py/mkenv.mk
+++ b/py/mkenv.mk
@@ -67,9 +67,9 @@ CXX += -m32
 LD += -m32
 endif
 
-MAKE_FROZEN = $(TOP)/tools/make-frozen.py
+MAKE_FROZEN = $(PYTHON) $(TOP)/tools/make-frozen.py
 MPY_CROSS = $(TOP)/mpy-cross/mpy-cross
-MPY_TOOL = $(TOP)/tools/mpy-tool.py
+MPY_TOOL = $(PYTHON) $(TOP)/tools/mpy-tool.py
 PREPROCESS_FROZEN_MODULES = PYTHONPATH=$(TOP)/tools/python-semver $(TOP)/tools/preprocess_frozen_modules.py
 
 all:
diff --git a/py/mkrules.mk b/py/mkrules.mk
index ed66da64b..57a51194a 100644
--- a/py/mkrules.mk
+++ b/py/mkrules.mk
@@ -46,16 +46,14 @@ vpath %.c . $(TOP)
 $(BUILD)/%.o: %.c
 	$(call compile_c)
 
+QSTR_GEN_EXTRA_CFLAGS += -DNO_QSTR
+
 # frozen.c and frozen_mpy.c are created in $(BUILD), so use our rule
 # for those as well.
 vpath %.c . $(BUILD)
 $(BUILD)/%.o: %.c
 	$(call compile_c)
 
-# List all native flags since the current build system doesn't have
-# the MicroPython configuration available. However, these flags are
-# needed to extract all qstrings
-QSTR_GEN_EXTRA_CFLAGS += -DNO_QSTR -DN_X64 -DN_X86 -DN_THUMB -DN_ARM -DN_XTENSA
 QSTR_GEN_EXTRA_CFLAGS += -I$(BUILD)/tmp
 
 vpath %.c . $(TOP)
@@ -75,9 +73,13 @@ $(BUILD)/%.pp: %.c
 # to get built before we try to compile any of them.
 $(OBJ): | $(HEADER_BUILD)/qstrdefs.generated.h $(HEADER_BUILD)/mpversion.h
 
-$(HEADER_BUILD)/qstr.i.last: $(SRC_QSTR) | $(HEADER_BUILD)/mpversion.h
+# The logic for qstr regeneration is:
+# - if anything in QSTR_GLOBAL_DEPENDENCIES is newer, then process all source files ($^)
+# - else, if list of newer prerequisites ($?) is not empty, then process just these ($?)
+# - else, process all source files ($^) [this covers "make -B" which can set $? to empty]
+$(HEADER_BUILD)/qstr.i.last: $(SRC_QSTR) $(QSTR_GLOBAL_DEPENDENCIES) | $(HEADER_BUILD)/mpversion.h
 	$(ECHO) "GEN $@"
-	$(Q)$(CPP) $(QSTR_GEN_EXTRA_CFLAGS) $(CFLAGS) $(if $?,$?,$^) >$(HEADER_BUILD)/qstr.i.last;
+	$(Q)$(CPP) $(QSTR_GEN_EXTRA_CFLAGS) $(CFLAGS) $(if $(filter $?,$(QSTR_GLOBAL_DEPENDENCIES)),$^,$(if $?,$?,$^)) >$(HEADER_BUILD)/qstr.i.last;
 
 $(HEADER_BUILD)/qstr.split: $(HEADER_BUILD)/qstr.i.last
 	$(STEPECHO) "GEN $@"
@@ -130,7 +132,7 @@ xargs -n1 "$(abspath $(MPY_CROSS))" $(MPY_CROSS_FLAGS)
 # if the default will not work (mpz is the default).
 $(BUILD)/frozen_mpy.c: $(BUILD)/frozen_mpy $(BUILD)/genhdr/qstrdefs.generated.h
 	$(STEPECHO) "Creating $@"
-	$(Q)$(PYTHON) $(MPY_TOOL) $(MPY_TOOL_LONGINT_IMPL) -f -q $(BUILD)/genhdr/qstrdefs.preprocessed.h $(shell $(FIND) -L $(BUILD)/frozen_mpy -type f -name '*.mpy') > $@
+	$(Q)$(MPY_TOOL) $(MPY_TOOL_LONGINT_IMPL) -f -q $(BUILD)/genhdr/qstrdefs.preprocessed.h $(shell $(FIND) -L $(BUILD)/frozen_mpy -type f -name '*.mpy') > $@
 endif
 
 ifneq ($(PROG),)
@@ -171,6 +173,27 @@ clean:
 	$(RM) -rf $(BUILD) $(CLEAN_EXTRA)
 .PHONY: clean
 
+# Clean every non-git file from FROZEN_DIR/FROZEN_MPY_DIR, but making a backup.
+# We run rmdir below to avoid empty backup dir (it will silently fail if backup
+# is non-empty).
+clean-frozen:
+	if [ -n "$(FROZEN_MPY_DIR)" ]; then \
+	backup_dir=$(FROZEN_MPY_DIR).$$(date +%Y%m%dT%H%M%S); mkdir $$backup_dir; \
+	cd $(FROZEN_MPY_DIR); git status --ignored -u all -s . | awk ' {print $$2}' \
+	| xargs --no-run-if-empty cp --parents -t ../$$backup_dir; \
+	rmdir ../$$backup_dir 2>/dev/null || true; \
+	git clean -d -f .; \
+	fi
+
+	if [ -n "$(FROZEN_DIR)" ]; then \
+	backup_dir=$(FROZEN_DIR).$$(date +%Y%m%dT%H%M%S); mkdir $$backup_dir; \
+	cd $(FROZEN_DIR); git status --ignored -u all -s . | awk ' {print $$2}' \
+	| xargs --no-run-if-empty cp --parents -t ../$$backup_dir; \
+	rmdir ../$$backup_dir 2>/dev/null || true; \
+	git clean -d -f .; \
+	fi
+.PHONY: clean-frozen
+
 print-cfg:
 	$(ECHO) "PY_SRC = $(PY_SRC)"
 	$(ECHO) "BUILD  = $(BUILD)"
diff --git a/py/modbuiltins.c b/py/modbuiltins.c
index cea87b181..eb1a17204 100644
--- a/py/modbuiltins.c
+++ b/py/modbuiltins.c
@@ -137,7 +137,7 @@ MP_DEFINE_CONST_FUN_OBJ_1(mp_builtin_callable_obj, mp_builtin_callable);
 STATIC mp_obj_t mp_builtin_chr(mp_obj_t o_in) {
     #if MICROPY_PY_BUILTINS_STR_UNICODE
     mp_uint_t c = mp_obj_get_int(o_in);
-    char str[4];
+    uint8_t str[4];
     int len = 0;
     if (c < 0x80) {
         *str = c; len = 1;
@@ -159,12 +159,12 @@ STATIC mp_obj_t mp_builtin_chr(mp_obj_t o_in) {
     } else {
         mp_raise_ValueError("chr() arg not in range(0x110000)");
     }
-    return mp_obj_new_str(str, len, true);
+    return mp_obj_new_str_via_qstr((char*)str, len);
     #else
     mp_int_t ord = mp_obj_get_int(o_in);
     if (0 <= ord && ord <= 0xff) {
-        char str[1] = {ord};
-        return mp_obj_new_str(str, 1, true);
+        uint8_t str[1] = {ord};
+        return mp_obj_new_str_via_qstr((char*)str, 1);
     } else {
         mp_raise_ValueError("chr() arg not in range(256)");
     }
@@ -173,46 +173,31 @@ STATIC mp_obj_t mp_builtin_chr(mp_obj_t o_in) {
 MP_DEFINE_CONST_FUN_OBJ_1(mp_builtin_chr_obj, mp_builtin_chr);
 
 STATIC mp_obj_t mp_builtin_dir(size_t n_args, const mp_obj_t *args) {
-    // TODO make this function more general and less of a hack
-
-    mp_obj_dict_t *dict = NULL;
-    mp_map_t *members = NULL;
-    if (n_args == 0) {
-        // make a list of names in the local name space
-        dict = mp_locals_get();
-    } else { // n_args == 1
-        // make a list of names in the given object
-        if (MP_OBJ_IS_TYPE(args[0], &mp_type_module)) {
-            dict = mp_obj_module_get_globals(args[0]);
-        } else {
-            mp_obj_type_t *type;
-            if (MP_OBJ_IS_TYPE(args[0], &mp_type_type)) {
-                type = MP_OBJ_TO_PTR(args[0]);
-            } else {
-                type = mp_obj_get_type(args[0]);
-            }
-            if (type->locals_dict != NULL && type->locals_dict->base.type == &mp_type_dict) {
-                dict = type->locals_dict;
-            }
-        }
-        if (mp_obj_is_instance_type(mp_obj_get_type(args[0]))) {
-            mp_obj_instance_t *inst = MP_OBJ_TO_PTR(args[0]);
-            members = &inst->members;
-        }
-    }
-
     mp_obj_t dir = mp_obj_new_list(0, NULL);
-    if (dict != NULL) {
+    if (n_args == 0) {
+        // Make a list of names in the local namespace
+        mp_obj_dict_t *dict = mp_locals_get();
         for (size_t i = 0; i < dict->map.alloc; i++) {
             if (MP_MAP_SLOT_IS_FILLED(&dict->map, i)) {
                 mp_obj_list_append(dir, dict->map.table[i].key);
             }
         }
-    }
-    if (members != NULL) {
-        for (size_t i = 0; i < members->alloc; i++) {
-            if (MP_MAP_SLOT_IS_FILLED(members, i)) {
-                mp_obj_list_append(dir, members->table[i].key);
+    } else { // n_args == 1
+        // Make a list of names in the given object
+        // Implemented by probing all possible qstrs with mp_load_method_maybe
+        size_t nqstr = QSTR_TOTAL();
+        for (size_t i = MP_QSTR_ + 1; i < nqstr; ++i) {
+            mp_obj_t dest[2];
+            mp_load_method_protected(args[0], i, dest, false);
+            if (dest[0] != MP_OBJ_NULL) {
+                #if MICROPY_PY_ALL_SPECIAL_METHODS
+                // Support for __dir__: see if we can dispatch to this special method
+                // This relies on MP_QSTR__dir__ being first after MP_QSTR_
+                if (i == MP_QSTR___dir__ && dest[1] != MP_OBJ_NULL) {
+                    return mp_call_method_n_kw(0, 0, dest);
+                }
+                #endif
+                mp_obj_list_append(dir, MP_OBJ_NEW_QSTR(i));
             }
         }
     }
@@ -343,19 +328,19 @@ MP_DEFINE_CONST_FUN_OBJ_1(mp_builtin_oct_obj, mp_builtin_oct);
 
 STATIC mp_obj_t mp_builtin_ord(mp_obj_t o_in) {
     size_t len;
-    const char *str = mp_obj_str_get_data(o_in, &len);
+    const byte *str = (const byte*)mp_obj_str_get_data(o_in, &len);
     #if MICROPY_PY_BUILTINS_STR_UNICODE
     if (MP_OBJ_IS_STR(o_in)) {
-        len = unichar_charlen(str, len);
+        len = utf8_charlen(str, len);
         if (len == 1) {
-            return mp_obj_new_int(utf8_get_char((const byte*)str));
+            return mp_obj_new_int(utf8_get_char(str));
         }
     } else
     #endif
     {
         // a bytes object, or a str without unicode support (don't sign extend the char)
         if (len == 1) {
-            return MP_OBJ_NEW_SMALL_INT(((const byte*)str)[0]);
+            return MP_OBJ_NEW_SMALL_INT(str[0]);
         }
     }
 
@@ -383,46 +368,52 @@ STATIC mp_obj_t mp_builtin_pow(size_t n_args, const mp_obj_t *args) {
 }
 MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mp_builtin_pow_obj, 2, 3, mp_builtin_pow);
 
-STATIC mp_obj_t mp_builtin_print(size_t n_args, const mp_obj_t *args, mp_map_t *kwargs) {
-    mp_map_elem_t *sep_elem = mp_map_lookup(kwargs, MP_OBJ_NEW_QSTR(MP_QSTR_sep), MP_MAP_LOOKUP);
-    mp_map_elem_t *end_elem = mp_map_lookup(kwargs, MP_OBJ_NEW_QSTR(MP_QSTR_end), MP_MAP_LOOKUP);
-    const char *sep_data = " ";
-    size_t sep_len = 1;
-    const char *end_data = "\n";
-    size_t end_len = 1;
-    if (sep_elem != NULL && sep_elem->value != mp_const_none) {
-        sep_data = mp_obj_str_get_data(sep_elem->value, &sep_len);
-    }
-    if (end_elem != NULL && end_elem->value != mp_const_none) {
-        end_data = mp_obj_str_get_data(end_elem->value, &end_len);
-    }
-    #if MICROPY_PY_IO && MICROPY_PY_SYS_STDFILES
-    void *stream_obj = &mp_sys_stdout_obj;
-    mp_map_elem_t *file_elem = mp_map_lookup(kwargs, MP_OBJ_NEW_QSTR(MP_QSTR_file), MP_MAP_LOOKUP);
-    if (file_elem != NULL && file_elem->value != mp_const_none) {
-        stream_obj = MP_OBJ_TO_PTR(file_elem->value); // XXX may not be a concrete object
-    }
+STATIC mp_obj_t mp_builtin_print(size_t n_args, const mp_obj_t *pos_args, mp_map_t *kw_args) {
+    enum { ARG_sep, ARG_end, ARG_file };
+    static const mp_arg_t allowed_args[] = {
+        { MP_QSTR_sep, MP_ARG_KW_ONLY | MP_ARG_OBJ, {.u_rom_obj = MP_ROM_QSTR(MP_QSTR__space_)} },
+        { MP_QSTR_end, MP_ARG_KW_ONLY | MP_ARG_OBJ, {.u_rom_obj = MP_ROM_QSTR(MP_QSTR__0x0a_)} },
+        #if MICROPY_PY_IO && MICROPY_PY_SYS_STDFILES
+        { MP_QSTR_file, MP_ARG_KW_ONLY | MP_ARG_OBJ, {.u_rom_obj = MP_ROM_PTR(&mp_sys_stdout_obj)} },
+        #endif
+    };
+
+    // parse args (a union is used to reduce the amount of C stack that is needed)
+    union {
+        mp_arg_val_t args[MP_ARRAY_SIZE(allowed_args)];
+        size_t len[2];
+    } u;
+    mp_arg_parse_all(0, NULL, kw_args, MP_ARRAY_SIZE(allowed_args), allowed_args, u.args);
 
-    mp_print_t print = {stream_obj, mp_stream_write_adaptor};
+    #if MICROPY_PY_IO && MICROPY_PY_SYS_STDFILES
+    mp_get_stream_raise(u.args[ARG_file].u_obj, MP_STREAM_OP_WRITE);
+    mp_print_t print = {MP_OBJ_TO_PTR(u.args[ARG_file].u_obj), mp_stream_write_adaptor};
     #endif
+
+    // extract the objects first because we are going to use the other part of the union
+    mp_obj_t sep = u.args[ARG_sep].u_obj;
+    mp_obj_t end = u.args[ARG_end].u_obj;
+    const char *sep_data = mp_obj_str_get_data(sep, &u.len[0]);
+    const char *end_data = mp_obj_str_get_data(end, &u.len[1]);
+
     for (size_t i = 0; i < n_args; i++) {
         if (i > 0) {
             #if MICROPY_PY_IO && MICROPY_PY_SYS_STDFILES
-            mp_stream_write_adaptor(stream_obj, sep_data, sep_len);
+            mp_stream_write_adaptor(print.data, sep_data, u.len[0]);
             #else
-            mp_print_strn(&mp_plat_print, sep_data, sep_len, 0, 0, 0);
+            mp_print_strn(&mp_plat_print, sep_data, u.len[0], 0, 0, 0);
             #endif
         }
         #if MICROPY_PY_IO && MICROPY_PY_SYS_STDFILES
-        mp_obj_print_helper(&print, args[i], PRINT_STR);
+        mp_obj_print_helper(&print, pos_args[i], PRINT_STR);
         #else
-        mp_obj_print_helper(&mp_plat_print, args[i], PRINT_STR);
+        mp_obj_print_helper(&mp_plat_print, pos_args[i], PRINT_STR);
         #endif
     }
     #if MICROPY_PY_IO && MICROPY_PY_SYS_STDFILES
-    mp_stream_write_adaptor(stream_obj, end_data, end_len);
+    mp_stream_write_adaptor(print.data, end_data, u.len[1]);
     #else
-    mp_print_strn(&mp_plat_print, end_data, end_len, 0, 0, 0);
+    mp_print_strn(&mp_plat_print, end_data, u.len[1], 0, 0, 0);
     #endif
     return mp_const_none;
 }
@@ -454,19 +445,46 @@ MP_DEFINE_CONST_FUN_OBJ_1(mp_builtin_repr_obj, mp_builtin_repr);
 STATIC mp_obj_t mp_builtin_round(size_t n_args, const mp_obj_t *args) {
     mp_obj_t o_in = args[0];
     if (MP_OBJ_IS_INT(o_in)) {
-        return o_in;
+        if (n_args <= 1) {
+            return o_in;
+        }
+
+        #if !MICROPY_PY_BUILTINS_ROUND_INT
+        mp_raise_NotImplementedError(NULL);
+        #else
+        mp_int_t num_dig = mp_obj_get_int(args[1]);
+        if (num_dig >= 0) {
+            return o_in;
+        }
+
+        mp_obj_t mult = mp_binary_op(MP_BINARY_OP_POWER, MP_OBJ_NEW_SMALL_INT(10), MP_OBJ_NEW_SMALL_INT(-num_dig));
+        mp_obj_t half_mult =  mp_binary_op(MP_BINARY_OP_FLOOR_DIVIDE, mult, MP_OBJ_NEW_SMALL_INT(2));
+        mp_obj_t modulo = mp_binary_op(MP_BINARY_OP_MODULO, o_in, mult);
+        mp_obj_t rounded = mp_binary_op(MP_BINARY_OP_SUBTRACT, o_in, modulo);
+        if (mp_obj_is_true(mp_binary_op(MP_BINARY_OP_MORE, half_mult, modulo))) {
+            return rounded;
+        } else if (mp_obj_is_true(mp_binary_op(MP_BINARY_OP_MORE, modulo, half_mult))) {
+            return mp_binary_op(MP_BINARY_OP_ADD, rounded, mult);
+        } else {
+            // round to even number
+            mp_obj_t floor = mp_binary_op(MP_BINARY_OP_FLOOR_DIVIDE, o_in, mult);
+            if (mp_obj_is_true(mp_binary_op(MP_BINARY_OP_AND, floor, MP_OBJ_NEW_SMALL_INT(1)))) {
+                return mp_binary_op(MP_BINARY_OP_ADD, rounded, mult);
+            } else {
+                return rounded;
+            }
+        }
+        #endif
     }
 #if MICROPY_PY_BUILTINS_FLOAT
-    mp_int_t num_dig = 0;
+    mp_float_t val = mp_obj_get_float(o_in);
     if (n_args > 1) {
-        num_dig = mp_obj_get_int(args[1]);
-        mp_float_t val = mp_obj_get_float(o_in);
+        mp_int_t num_dig = mp_obj_get_int(args[1]);
         mp_float_t mult = MICROPY_FLOAT_C_FUN(pow)(10, num_dig);
         // TODO may lead to overflow
         mp_float_t rounded = MICROPY_FLOAT_C_FUN(nearbyint)(val * mult) / mult;
         return mp_obj_new_float(rounded);
     }
-    mp_float_t val = mp_obj_get_float(o_in);
     mp_float_t rounded = MICROPY_FLOAT_C_FUN(nearbyint)(val);
     return mp_obj_new_int_from_float(rounded);
 #else
@@ -543,14 +561,8 @@ MP_DEFINE_CONST_FUN_OBJ_2(mp_builtin_delattr_obj, mp_builtin_delattr);
 
 STATIC mp_obj_t mp_builtin_hasattr(mp_obj_t object_in, mp_obj_t attr_in) {
     qstr attr = mp_obj_str_get_qstr(attr_in);
-
     mp_obj_t dest[2];
-    // TODO: https://docs.python.org/3/library/functions.html?highlight=hasattr#hasattr
-    // explicitly says "This is implemented by calling getattr(object, name) and seeing
-    // whether it raises an AttributeError or not.", so we should explicitly wrap this
-    // in nlr_push and handle exception.
-    mp_load_method_maybe(object_in, attr, dest);
-
+    mp_load_method_protected(object_in, attr, dest, false);
     return mp_obj_new_bool(dest[0] != MP_OBJ_NULL);
 }
 MP_DEFINE_CONST_FUN_OBJ_2(mp_builtin_hasattr_obj, mp_builtin_hasattr);
diff --git a/py/modcollections.c b/py/modcollections.c
index 837ec2f92..91e735528 100644
--- a/py/modcollections.c
+++ b/py/modcollections.c
@@ -30,6 +30,9 @@
 
 STATIC const mp_rom_map_elem_t mp_module_collections_globals_table[] = {
     { MP_ROM_QSTR(MP_QSTR___name__), MP_ROM_QSTR(MP_QSTR_collections) },
+    #if MICROPY_PY_COLLECTIONS_DEQUE
+    { MP_ROM_QSTR(MP_QSTR_deque), MP_ROM_PTR(&mp_type_deque) },
+    #endif
     { MP_ROM_QSTR(MP_QSTR_namedtuple), MP_ROM_PTR(&mp_namedtuple_obj) },
     #if MICROPY_PY_COLLECTIONS_ORDEREDDICT
     { MP_ROM_QSTR(MP_QSTR_OrderedDict), MP_ROM_PTR(&mp_type_ordereddict) },
diff --git a/py/modio.c b/py/modio.c
index 9263b5949..9b09de96e 100644
--- a/py/modio.c
+++ b/py/modio.c
@@ -30,6 +30,8 @@
 #include "py/runtime.h"
 #include "py/builtin.h"
 #include "py/stream.h"
+#include "py/binary.h"
+#include "py/objarray.h"
 #include "py/objstringio.h"
 #include "py/frozenmod.h"
 
@@ -38,6 +40,70 @@
 extern const mp_obj_type_t mp_type_fileio;
 extern const mp_obj_type_t mp_type_textio;
 
+#if MICROPY_PY_IO_IOBASE
+
+STATIC const mp_obj_type_t mp_type_iobase;
+
+STATIC mp_obj_base_t iobase_singleton = {&mp_type_iobase};
+
+STATIC mp_obj_t iobase_make_new(const mp_obj_type_t *type, size_t n_args, size_t n_kw, const mp_obj_t *args) {
+    (void)type;
+    (void)n_args;
+    (void)n_kw;
+    (void)args;
+    return MP_OBJ_FROM_PTR(&iobase_singleton);
+}
+
+STATIC mp_uint_t iobase_read_write(mp_obj_t obj, void *buf, mp_uint_t size, int *errcode, qstr qst) {
+    mp_obj_t dest[3];
+    mp_load_method(obj, qst, dest);
+    mp_obj_array_t ar = {{&mp_type_bytearray}, BYTEARRAY_TYPECODE, 0, size, buf};
+    dest[2] = MP_OBJ_FROM_PTR(&ar);
+    mp_obj_t ret = mp_call_method_n_kw(1, 0, dest);
+    if (ret == mp_const_none) {
+        *errcode = MP_EAGAIN;
+        return MP_STREAM_ERROR;
+    } else {
+        return mp_obj_get_int(ret);
+    }
+}
+STATIC mp_uint_t iobase_read(mp_obj_t obj, void *buf, mp_uint_t size, int *errcode) {
+    return iobase_read_write(obj, buf, size, errcode, MP_QSTR_readinto);
+}
+
+STATIC mp_uint_t iobase_write(mp_obj_t obj, const void *buf, mp_uint_t size, int *errcode) {
+    return iobase_read_write(obj, (void*)buf, size, errcode, MP_QSTR_write);
+}
+
+STATIC mp_uint_t iobase_ioctl(mp_obj_t obj, mp_uint_t request, uintptr_t arg, int *errcode) {
+    mp_obj_t dest[4];
+    mp_load_method(obj, MP_QSTR_ioctl, dest);
+    dest[2] = mp_obj_new_int_from_uint(request);
+    dest[3] = mp_obj_new_int_from_uint(arg);
+    mp_int_t ret = mp_obj_get_int(mp_call_method_n_kw(2, 0, dest));
+    if (ret >= 0) {
+        return ret;
+    } else {
+        *errcode = -ret;
+        return MP_STREAM_ERROR;
+    }
+}
+
+STATIC const mp_stream_p_t iobase_p = {
+    .read = iobase_read,
+    .write = iobase_write,
+    .ioctl = iobase_ioctl,
+};
+
+STATIC const mp_obj_type_t mp_type_iobase = {
+    { &mp_type_type },
+    .name = MP_QSTR_IOBase,
+    .make_new = iobase_make_new,
+    .protocol = &iobase_p,
+};
+
+#endif // MICROPY_PY_IO_IOBASE
+
 #if MICROPY_PY_IO_BUFFEREDWRITER
 typedef struct _mp_obj_bufwriter_t {
     mp_obj_base_t base;
@@ -131,7 +197,7 @@ STATIC const mp_obj_type_t bufwriter_type = {
 };
 #endif // MICROPY_PY_IO_BUFFEREDWRITER
 
-#if MICROPY_MODULE_FROZEN_STR
+#if MICROPY_PY_IO_RESOURCE_STREAM
 STATIC mp_obj_t resource_stream(mp_obj_t package_in, mp_obj_t path_in) {
     VSTR_FIXED(path_buf, MICROPY_ALLOC_PATH_MAX);
     size_t len;
@@ -176,10 +242,10 @@ STATIC mp_obj_t resource_stream(mp_obj_t package_in, mp_obj_t path_in) {
         return MP_OBJ_FROM_PTR(o);
     }
 
-    mp_obj_t path_out = mp_obj_new_str(path_buf.buf, path_buf.len, false);
+    mp_obj_t path_out = mp_obj_new_str(path_buf.buf, path_buf.len);
     return mp_builtin_open(1, &path_out, (mp_map_t*)&mp_const_empty_map);
 }
-MP_DEFINE_CONST_FUN_OBJ_2(resource_stream_obj, resource_stream);
+STATIC MP_DEFINE_CONST_FUN_OBJ_2(resource_stream_obj, resource_stream);
 #endif
 
 STATIC const mp_rom_map_elem_t mp_module_io_globals_table[] = {
@@ -187,6 +253,9 @@ STATIC const mp_rom_map_elem_t mp_module_io_globals_table[] = {
     // Note: mp_builtin_open_obj should be defined by port, it's not
     // part of the core.
     { MP_ROM_QSTR(MP_QSTR_open), MP_ROM_PTR(&mp_builtin_open_obj) },
+    #if MICROPY_PY_IO_IOBASE
+    { MP_ROM_QSTR(MP_QSTR_IOBase), MP_ROM_PTR(&mp_type_iobase) },
+    #endif
     #if MICROPY_PY_IO_RESOURCE_STREAM
     { MP_ROM_QSTR(MP_QSTR_resource_stream), MP_ROM_PTR(&resource_stream_obj) },
     #endif
diff --git a/py/modmicropython.c b/py/modmicropython.c
index 2aac53adc..864d1a5c5 100644
--- a/py/modmicropython.c
+++ b/py/modmicropython.c
@@ -35,6 +35,7 @@
 // Various builtins specific to MicroPython runtime,
 // living in micropython module
 
+#if MICROPY_ENABLE_COMPILER
 STATIC mp_obj_t mp_micropython_opt_level(size_t n_args, const mp_obj_t *args) {
     if (n_args == 0) {
         return MP_OBJ_NEW_SMALL_INT(MP_STATE_VM(mp_optimise_value));
@@ -44,6 +45,7 @@ STATIC mp_obj_t mp_micropython_opt_level(size_t n_args, const mp_obj_t *args) {
     }
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mp_micropython_opt_level_obj, 0, 1, mp_micropython_opt_level);
+#endif
 
 #if MICROPY_PY_MICROPYTHON_MEM_INFO
 
@@ -103,14 +105,21 @@ STATIC mp_obj_t mp_micropython_qstr_info(size_t n_args, const mp_obj_t *args) {
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mp_micropython_qstr_info_obj, 0, 1, mp_micropython_qstr_info);
 
-#if MICROPY_STACK_CHECK
+#endif // MICROPY_PY_MICROPYTHON_MEM_INFO
+
+#if MICROPY_PY_MICROPYTHON_STACK_USE
 STATIC mp_obj_t mp_micropython_stack_use(void) {
     return MP_OBJ_NEW_SMALL_INT(mp_stack_usage());
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_0(mp_micropython_stack_use_obj, mp_micropython_stack_use);
 #endif
 
-#endif // MICROPY_PY_MICROPYTHON_MEM_INFO
+#if MICROPY_ENABLE_PYSTACK
+STATIC mp_obj_t mp_micropython_pystack_use(void) {
+    return MP_OBJ_NEW_SMALL_INT(mp_pystack_usage());
+}
+STATIC MP_DEFINE_CONST_FUN_OBJ_0(mp_micropython_pystack_use_obj, mp_micropython_pystack_use);
+#endif
 
 #if MICROPY_ENABLE_GC
 STATIC mp_obj_t mp_micropython_heap_lock(void) {
@@ -151,7 +160,9 @@ STATIC MP_DEFINE_CONST_FUN_OBJ_2(mp_micropython_schedule_obj, mp_micropython_sch
 STATIC const mp_rom_map_elem_t mp_module_micropython_globals_table[] = {
     { MP_ROM_QSTR(MP_QSTR___name__), MP_ROM_QSTR(MP_QSTR_micropython) },
     { MP_ROM_QSTR(MP_QSTR_const), MP_ROM_PTR(&mp_identity_obj) },
+    #if MICROPY_ENABLE_COMPILER
     { MP_ROM_QSTR(MP_QSTR_opt_level), MP_ROM_PTR(&mp_micropython_opt_level_obj) },
+    #endif
 #if MICROPY_PY_MICROPYTHON_MEM_INFO
 #if MICROPY_MEM_STATS
     { MP_ROM_QSTR(MP_QSTR_mem_total), MP_ROM_PTR(&mp_micropython_mem_total_obj) },
@@ -160,13 +171,16 @@ STATIC const mp_rom_map_elem_t mp_module_micropython_globals_table[] = {
 #endif
     { MP_ROM_QSTR(MP_QSTR_mem_info), MP_ROM_PTR(&mp_micropython_mem_info_obj) },
     { MP_ROM_QSTR(MP_QSTR_qstr_info), MP_ROM_PTR(&mp_micropython_qstr_info_obj) },
-    #if MICROPY_STACK_CHECK
+#endif
+    #if MICROPY_PY_MICROPYTHON_STACK_USE
     { MP_ROM_QSTR(MP_QSTR_stack_use), MP_ROM_PTR(&mp_micropython_stack_use_obj) },
     #endif
-#endif
 #if MICROPY_ENABLE_EMERGENCY_EXCEPTION_BUF && (MICROPY_EMERGENCY_EXCEPTION_BUF_SIZE == 0)
     { MP_ROM_QSTR(MP_QSTR_alloc_emergency_exception_buf), MP_ROM_PTR(&mp_alloc_emergency_exception_buf_obj) },
 #endif
+    #if MICROPY_ENABLE_PYSTACK
+    { MP_ROM_QSTR(MP_QSTR_pystack_use), MP_ROM_PTR(&mp_micropython_pystack_use_obj) },
+    #endif
     #if MICROPY_ENABLE_GC
     { MP_ROM_QSTR(MP_QSTR_heap_lock), MP_ROM_PTR(&mp_micropython_heap_lock_obj) },
     { MP_ROM_QSTR(MP_QSTR_heap_unlock), MP_ROM_PTR(&mp_micropython_heap_unlock_obj) },
diff --git a/py/modsys.c b/py/modsys.c
index de3cb7e1f..e32841923 100644
--- a/py/modsys.c
+++ b/py/modsys.c
@@ -106,7 +106,8 @@ STATIC mp_obj_t mp_sys_print_exception(size_t n_args, const mp_obj_t *args) {
     #if MICROPY_PY_IO && MICROPY_PY_SYS_STDFILES
     void *stream_obj = &mp_sys_stdout_obj;
     if (n_args > 1) {
-        stream_obj = MP_OBJ_TO_PTR(args[1]); // XXX may fail
+        mp_get_stream_raise(args[1], MP_STREAM_OP_WRITE);
+        stream_obj = MP_OBJ_TO_PTR(args[1]);
     }
 
     mp_print_t print = {stream_obj, mp_stream_write_adaptor};
@@ -140,10 +141,12 @@ STATIC mp_obj_t mp_sys_exc_info(void) {
 MP_DEFINE_CONST_FUN_OBJ_0(mp_sys_exc_info_obj, mp_sys_exc_info);
 #endif
 
+#if MICROPY_PY_SYS_GETSIZEOF
 STATIC mp_obj_t mp_sys_getsizeof(mp_obj_t obj) {
     return mp_unary_op(MP_UNARY_OP_SIZEOF, obj);
 }
-MP_DEFINE_CONST_FUN_OBJ_1(mp_sys_getsizeof_obj, mp_sys_getsizeof);
+STATIC MP_DEFINE_CONST_FUN_OBJ_1(mp_sys_getsizeof_obj, mp_sys_getsizeof);
+#endif
 
 STATIC const mp_rom_map_elem_t mp_module_sys_globals_table[] = {
     { MP_ROM_QSTR(MP_QSTR___name__), MP_ROM_QSTR(MP_QSTR_sys) },
diff --git a/py/modthread.c b/py/modthread.c
index cb071d0f8..61ada5035 100644
--- a/py/modthread.c
+++ b/py/modthread.c
@@ -165,6 +165,12 @@ STATIC void *thread_entry(void *args_in) {
     mp_stack_set_top(&ts + 1); // need to include ts in root-pointer scan
     mp_stack_set_limit(args->stack_size);
 
+    #if MICROPY_ENABLE_PYSTACK
+    // TODO threading and pystack is not fully supported, for now just make a small stack
+    mp_obj_t mini_pystack[128];
+    mp_pystack_init(mini_pystack, &mini_pystack[128]);
+    #endif
+
     // set locals and globals from the calling context
     mp_locals_set(args->dict_locals);
     mp_globals_set(args->dict_globals);
diff --git a/py/mpconfig.h b/py/mpconfig.h
index 74d7c2c92..52a7c05a2 100755
--- a/py/mpconfig.h
+++ b/py/mpconfig.h
@@ -79,7 +79,7 @@
 //  - seeeeeee eeeeffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff 64-bit fp, e != 0x7ff
 //  - s1111111 11110000 00000000 00000000 00000000 00000000 00000000 00000000 +/- inf
 //  - 01111111 11111000 00000000 00000000 00000000 00000000 00000000 00000000 normalised nan
-//  - 01111111 11111101 00000000 00000000 iiiiiiii iiiiiiii iiiiiiii iiiiiii1 small int
+//  - 01111111 11111101 iiiiiiii iiiiiiii iiiiiiii iiiiiiii iiiiiiii iiiiiii1 small int
 //  - 01111111 11111110 00000000 00000000 qqqqqqqq qqqqqqqq qqqqqqqq qqqqqqq1 str
 //  - 01111111 11111100 00000000 00000000 pppppppp pppppppp pppppppp pppppp00 ptr (4 byte alignment)
 // Stored as O = R + 0x8004000000000000, retrieved as R = O - 0x8004000000000000.
@@ -353,7 +353,7 @@
 #endif
 
 // Whether to enable optimisation of: a, b, c = d, e, f
-// Cost 156 bytes (Thumb2)
+// Requires MICROPY_COMP_DOUBLE_TUPLE_ASSIGN and costs 68 bytes (Thumb2)
 #ifndef MICROPY_COMP_TRIPLE_TUPLE_ASSIGN
 #define MICROPY_COMP_TRIPLE_TUPLE_ASSIGN (0)
 #endif
@@ -411,6 +411,13 @@
 /*****************************************************************************/
 /* Python internal features                                                  */
 
+// Whether to enable import of external modules
+// When disabled, only importing of built-in modules is supported
+// When enabled, a port must implement mp_import_stat (among other things)
+#ifndef MICROPY_ENABLE_EXTERNAL_IMPORT
+#define MICROPY_ENABLE_EXTERNAL_IMPORT (1)
+#endif
+
 // Whether to use the POSIX reader for importing files
 #ifndef MICROPY_READER_POSIX
 #define MICROPY_READER_POSIX (0)
@@ -452,6 +459,17 @@
 #define MICROPY_ENABLE_FINALISER (0)
 #endif
 
+// Whether to enable a separate allocator for the Python stack.
+// If enabled then the code must call mp_pystack_init before mp_init.
+#ifndef MICROPY_ENABLE_PYSTACK
+#define MICROPY_ENABLE_PYSTACK (0)
+#endif
+
+// Number of bytes that memory returned by mp_pystack_alloc will be aligned by.
+#ifndef MICROPY_PYSTACK_ALIGN
+#define MICROPY_PYSTACK_ALIGN (8)
+#endif
+
 // Whether to check C stack usage. C stack used for calling Python functions,
 // etc. Not checking means segfault on overflow.
 #ifndef MICROPY_STACK_CHECK
@@ -679,22 +697,41 @@ typedef double mp_float_t;
 #define MICROPY_VFS (0)
 #endif
 
+// Support for VFS POSIX component, to mount a POSIX filesystem within VFS
+#ifndef MICROPY_VFS
+#define MICROPY_VFS_POSIX (0)
+#endif
+
+// Support for VFS FAT component, to mount a FAT filesystem within VFS
+#ifndef MICROPY_VFS
+#define MICROPY_VFS_FAT (0)
+#endif
+
 /*****************************************************************************/
 /* Fine control over Python builtins, classes, modules, etc                  */
 
+// Whether to support multiple inheritance of Python classes.  Multiple
+// inheritance makes some C functions inherently recursive, and adds a bit of
+// code overhead.
+#ifndef MICROPY_MULTIPLE_INHERITANCE
+#define MICROPY_MULTIPLE_INHERITANCE (1)
+#endif
+
 // Whether to implement attributes on functions
 #ifndef MICROPY_PY_FUNCTION_ATTRS
 #define MICROPY_PY_FUNCTION_ATTRS (0)
 #endif
 
-// Whether to support descriptors (__get__ and __set__)
-// This costs some code size and makes all load attrs and store attrs slow
+// Whether to support the descriptors __get__, __set__, __delete__
+// This costs some code size and makes load/store/delete of instance
+// attributes slower for the classes that use this feature
 #ifndef MICROPY_PY_DESCRIPTORS
 #define MICROPY_PY_DESCRIPTORS (0)
 #endif
 
 // Whether to support class __delattr__ and __setattr__ methods
-// This costs some code size and makes all del attrs and store attrs slow
+// This costs some code size and makes store/delete of instance
+// attributes slower for the classes that use this feature
 #ifndef MICROPY_PY_DELATTR_SETATTR
 #define MICROPY_PY_DELATTR_SETATTR (0)
 #endif
@@ -704,6 +741,15 @@ typedef double mp_float_t;
 #define MICROPY_PY_ASYNC_AWAIT (1)
 #endif
 
+// Non-standard .pend_throw() method for generators, allowing for
+// Future-like behavior with respect to exception handling: an
+// exception set with .pend_throw() will activate on the next call
+// to generator's .send() or .__next__(). (This is useful to implement
+// async schedulers.)
+#ifndef MICROPY_PY_GENERATOR_PEND_THROW
+#define MICROPY_PY_GENERATOR_PEND_THROW (1)
+#endif
+
 // Issue a warning when comparing str and bytes objects
 #ifndef MICROPY_PY_STR_BYTES_CMP_WARN
 #define MICROPY_PY_STR_BYTES_CMP_WARN (0)
@@ -776,6 +822,19 @@ typedef double mp_float_t;
 #define MICROPY_PY_BUILTINS_RANGE_ATTRS (1)
 #endif
 
+// Whether to support binary ops [only (in)equality is defined] between range
+// objects.  With this option disabled all range objects that are not exactly
+// the same object will compare as not-equal.  With it enabled the semantics
+// match CPython and ranges are equal if they yield the same sequence of items.
+#ifndef MICROPY_PY_BUILTINS_RANGE_BINOP
+#define MICROPY_PY_BUILTINS_RANGE_BINOP (0)
+#endif
+
+// Whether to support rounding of integers (incl bignum); eg round(123,-1)=120
+#ifndef MICROPY_PY_BUILTINS_ROUND_INT
+#define MICROPY_PY_BUILTINS_ROUND_INT (0)
+#endif
+
 // Whether to support timeout exceptions (like socket.timeout)
 #ifndef MICROPY_PY_BUILTINS_TIMEOUTERROR
 #define MICROPY_PY_BUILTINS_TIMEOUTERROR (0)
@@ -881,6 +940,11 @@ typedef double mp_float_t;
 #define MICROPY_PY_MICROPYTHON_MEM_INFO (0)
 #endif
 
+// Whether to provide "micropython.stack_use" function
+#ifndef MICROPY_PY_MICROPYTHON_STACK_USE
+#define MICROPY_PY_MICROPYTHON_STACK_USE (MICROPY_PY_MICROPYTHON_MEM_INFO)
+#endif
+
 // Whether to provide "array" module. Note that large chunk of the
 // underlying code is shared with "bytearray" builtin type, so to
 // get real savings, it should be disabled too.
@@ -911,11 +975,21 @@ typedef double mp_float_t;
 #define MICROPY_PY_COLLECTIONS (1)
 #endif
 
+// Whether to provide "ucollections.deque" type
+#ifndef MICROPY_PY_COLLECTIONS_DEQUE
+#define MICROPY_PY_COLLECTIONS_DEQUE (0)
+#endif
+
 // Whether to provide "collections.OrderedDict" type
 #ifndef MICROPY_PY_COLLECTIONS_ORDEREDDICT
 #define MICROPY_PY_COLLECTIONS_ORDEREDDICT (0)
 #endif
 
+// Whether to provide the _asdict function for namedtuple
+#ifndef MICROPY_PY_COLLECTIONS_NAMEDTUPLE__ASDICT
+#define MICROPY_PY_COLLECTIONS_NAMEDTUPLE__ASDICT (0)
+#endif
+
 // Whether to provide "math" module
 #ifndef MICROPY_PY_MATH
 #define MICROPY_PY_MATH (1)
@@ -946,9 +1020,18 @@ typedef double mp_float_t;
 #define MICROPY_PY_IO (1)
 #endif
 
+// Whether to provide "io.IOBase" class to support user streams
+#ifndef MICROPY_PY_IO_IOBASE
+#define MICROPY_PY_IO_IOBASE (0)
+#endif
+
 // Whether to provide "uio.resource_stream()" function with
 // the semantics of CPython's pkg_resources.resource_stream()
-// (allows to access resources in frozen packages).
+// (allows to access binary resources in frozen source packages).
+// Note that the same functionality can be achieved in "pure
+// Python" by prepocessing binary resources into Python source
+// and bytecode-freezing it (with a simple helper module available
+// e.g. in micropython-lib).
 #ifndef MICROPY_PY_IO_RESOURCE_STREAM
 #define MICROPY_PY_IO_RESOURCE_STREAM (0)
 #endif
@@ -1094,6 +1177,14 @@ typedef double mp_float_t;
 #define MICROPY_PY_UHASHLIB (0)
 #endif
 
+#ifndef MICROPY_PY_UHASHLIB_SHA1
+#define MICROPY_PY_UHASHLIB_SHA1  (0)
+#endif
+
+#ifndef MICROPY_PY_UHASHLIB_SHA256
+#define MICROPY_PY_UHASHLIB_SHA256 (1)
+#endif
+
 #ifndef MICROPY_PY_UBINASCII
 #define MICROPY_PY_UBINASCII (0)
 #endif
@@ -1217,29 +1308,26 @@ typedef double mp_float_t;
 #elif defined(MP_ENDIANNESS_BIG)
 #define MP_ENDIANNESS_LITTLE (!MP_ENDIANNESS_BIG)
 #else
-  // Endiannes not defined by port so try to autodetect it.
+  // Endianness not defined by port so try to autodetect it.
   #if defined(__BYTE_ORDER__)
     #if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
       #define MP_ENDIANNESS_LITTLE (1)
-    #else
+    #elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
       #define MP_ENDIANNESS_LITTLE (0)
     #endif
-  #elif defined(__LITTLE_ENDIAN__) || defined(__LITTLE_ENDIAN) || defined (_LITTLE_ENDIAN)
-    #define MP_ENDIANNESS_LITTLE (1)
-  #elif defined(__BIG_ENDIAN__) || defined(__BIG_ENDIAN) || defined (_BIG_ENDIAN)
-    #define MP_ENDIANNESS_LITTLE (0)
   #else
     #include <endian.h>
       #if defined(__BYTE_ORDER)
         #if __BYTE_ORDER == __LITTLE_ENDIAN
           #define MP_ENDIANNESS_LITTLE (1)
-        #else
+        #elif __BYTE_ORDER == __BIG_ENDIAN
           #define MP_ENDIANNESS_LITTLE (0)
         #endif
-      #else
-        #error endianness not defined and cannot detect it
       #endif
   #endif
+  #ifndef MP_ENDIANNESS_LITTLE
+    #error endianness not defined and cannot detect it
+  #endif
   #define MP_ENDIANNESS_BIG (!MP_ENDIANNESS_LITTLE)
 #endif
 
@@ -1315,4 +1403,24 @@ typedef double mp_float_t;
 #define MP_UNLIKELY(x) __builtin_expect((x), 0)
 #endif
 
+#ifndef MP_HTOBE16
+#if MP_ENDIANNESS_LITTLE
+# define MP_HTOBE16(x) ((uint16_t)( (((x) & 0xff) << 8) | (((x) >> 8) & 0xff) ))
+# define MP_BE16TOH(x) MP_HTOBE16(x)
+#else
+# define MP_HTOBE16(x) (x)
+# define MP_BE16TOH(x) (x)
+#endif
+#endif
+
+#ifndef MP_HTOBE32
+#if MP_ENDIANNESS_LITTLE
+# define MP_HTOBE32(x) ((uint32_t)( (((x) & 0xff) << 24) | (((x) & 0xff00) << 8) | (((x) >> 8)  & 0xff00) | (((x) >> 24) & 0xff) ))
+# define MP_BE32TOH(x) MP_HTOBE32(x)
+#else
+# define MP_HTOBE32(x) (x)
+# define MP_BE32TOH(x) (x)
+#endif
+#endif
+
 #endif // MICROPY_INCLUDED_PY_MPCONFIG_H
diff --git a/py/mperrno.h b/py/mperrno.h
index a028157ba..1eb342bc3 100644
--- a/py/mperrno.h
+++ b/py/mperrno.h
@@ -125,7 +125,7 @@
 #define MP_EPIPE            EPIPE
 #define MP_EDOM             EDOM
 #define MP_ERANGE           ERANGE
-#define MP_EWOULDBLOCK      EAGAIN
+#define MP_EWOULDBLOCK      EWOULDBLOCK
 #define MP_EOPNOTSUPP       EOPNOTSUPP
 #define MP_EAFNOSUPPORT     EAFNOSUPPORT
 #define MP_EADDRINUSE       EADDRINUSE
diff --git a/py/mpprint.c b/py/mpprint.c
index a569ef793..c2e65301c 100644
--- a/py/mpprint.c
+++ b/py/mpprint.c
@@ -446,11 +446,16 @@ int mp_vprintf(const mp_print_t *print, const char *fmt, va_list args) {
             }
         }
 
-        // parse long specifiers (current not used)
-        //bool long_arg = false;
+        // parse long specifiers (only for LP64 model where they make a difference)
+        #ifndef __LP64__
+        const
+        #endif
+        bool long_arg = false;
         if (*fmt == 'l') {
             ++fmt;
-            //long_arg = true;
+            #ifdef __LP64__
+            long_arg = true;
+            #endif
         }
 
         if (*fmt == '\0') {
@@ -505,14 +510,21 @@ int mp_vprintf(const mp_print_t *print, const char *fmt, va_list args) {
                 chrs += mp_print_int(print, va_arg(args, int), 1, 10, 'a', flags, fill, width);
                 break;
             case 'x':
-                chrs += mp_print_int(print, va_arg(args, unsigned int), 0, 16, 'a', flags, fill, width);
-                break;
-            case 'X':
-                chrs += mp_print_int(print, va_arg(args, unsigned int), 0, 16, 'A', flags, fill, width);
+            case 'X': {
+                char fmt_c = *fmt - 'X' + 'A';
+                mp_uint_t val;
+                if (long_arg) {
+                    val = va_arg(args, unsigned long int);
+                } else {
+                    val = va_arg(args, unsigned int);
+                }
+                chrs += mp_print_int(print, val, 0, 16, fmt_c, flags, fill, width);
                 break;
+            }
             case 'p':
             case 'P': // don't bother to handle upcase for 'P'
-                chrs += mp_print_int(print, va_arg(args, unsigned int), 0, 16, 'a', flags, fill, width);
+                // Use unsigned long int to work on both ILP32 and LP64 systems
+                chrs += mp_print_int(print, va_arg(args, unsigned long int), 0, 16, 'a', flags, fill, width);
                 break;
 #if MICROPY_PY_BUILTINS_FLOAT
             case 'e':
diff --git a/py/mpstate.h b/py/mpstate.h
index c50947066..6e68159ee 100644
--- a/py/mpstate.h
+++ b/py/mpstate.h
@@ -80,7 +80,6 @@ typedef struct _mp_state_mem_t {
 
     int gc_stack_overflow;
     size_t gc_stack[MICROPY_ALLOC_GC_STACK_SIZE];
-    size_t *gc_sp;
     uint16_t gc_lock_depth;
 
     // This variable controls auto garbage collection.  If set to false then the
@@ -109,10 +108,11 @@ typedef struct _mp_state_mem_t {
 // This structure hold runtime and VM information.  It includes a section
 // which contains root pointers that must be scanned by the GC.
 typedef struct _mp_state_vm_t {
-    ////////////////////////////////////////////////////////////
-    // START ROOT POINTER SECTION
-    // everything that needs GC scanning must go here
-    // this must start at the start of this structure
+    //
+    // CONTINUE ROOT POINTER SECTION
+    // This must start at the start of this structure and follows
+    // the state in the mp_state_thread_t structure, continuing
+    // the root pointer section from there.
     //
 
     qstr_pool_t *last_pool;
@@ -146,8 +146,6 @@ typedef struct _mp_state_vm_t {
     volatile mp_obj_t mp_pending_exception;
 
     #if MICROPY_ENABLE_SCHEDULER
-    volatile int16_t sched_state;
-    uint16_t sched_sp;
     mp_sched_item_t sched_stack[MICROPY_SCHEDULER_DEPTH];
     #endif
 
@@ -173,12 +171,15 @@ typedef struct _mp_state_vm_t {
 
     // root pointers for extmod
 
-    #ifdef MICROPY_PY_OS_DUPTERM
+    #if MICROPY_REPL_EVENT_DRIVEN
+    vstr_t *repl_line;
+    #endif
+
+    #if MICROPY_PY_OS_DUPTERM
     mp_obj_t dupterm_objs[MICROPY_PY_OS_DUPTERM];
-    mp_obj_t dupterm_arr_obj;
     #endif
 
-    #ifdef MICROPY_PY_LWIP_SLIP
+    #if MICROPY_PY_LWIP_SLIP
     mp_obj_t lwip_slip_stream;
     #endif
 
@@ -202,13 +203,20 @@ typedef struct _mp_state_vm_t {
     mp_thread_mutex_t qstr_mutex;
     #endif
 
+    #if MICROPY_ENABLE_COMPILER
     mp_uint_t mp_optimise_value;
+    #endif
 
     // size of the emergency exception buf, if it's dynamically allocated
     #if MICROPY_ENABLE_EMERGENCY_EXCEPTION_BUF && MICROPY_EMERGENCY_EXCEPTION_BUF_SIZE == 0
     mp_int_t mp_emergency_exception_buf_size;
     #endif
 
+    #if MICROPY_ENABLE_SCHEDULER
+    volatile int16_t sched_state;
+    uint16_t sched_sp;
+    #endif
+
     #if MICROPY_PY_THREAD_GIL
     // This is a global mutex used to make the VM/runtime thread-safe.
     mp_thread_mutex_t gil_mutex;
@@ -218,12 +226,6 @@ typedef struct _mp_state_vm_t {
 // This structure holds state that is specific to a given thread.
 // Everything in this structure is scanned for root pointers.
 typedef struct _mp_state_thread_t {
-    mp_obj_dict_t *dict_locals;
-    mp_obj_dict_t *dict_globals;
-
-    // Note: nlr asm code has the offset of this hard-coded
-    nlr_buf_t *nlr_top; // ROOT POINTER
-
     // Stack top at the start of program
     char *stack_top;
 
@@ -234,12 +236,27 @@ typedef struct _mp_state_thread_t {
     #if MICROPY_STACK_CHECK
     size_t stack_limit;
     #endif
+
+    #if MICROPY_ENABLE_PYSTACK
+    uint8_t *pystack_start;
+    uint8_t *pystack_end;
+    uint8_t *pystack_cur;
+    #endif
+
+    ////////////////////////////////////////////////////////////
+    // START ROOT POINTER SECTION
+    // Everything that needs GC scanning must start here, and
+    // is followed by state in the mp_state_vm_t structure.
+    //
+
+    mp_obj_dict_t *dict_locals;
+    mp_obj_dict_t *dict_globals;
+
+    nlr_buf_t *nlr_top;
 } mp_state_thread_t;
 
 // This structure combines the above 3 structures.
 // The order of the entries are important for root pointer scanning in the GC to work.
-// Note: if this structure changes then revisit all nlr asm code since they
-// have the offset of nlr_top hard-coded.
 typedef struct _mp_state_ctx_t {
     mp_state_thread_t thread;
     mp_state_vm_t vm;
diff --git a/py/mpz.c b/py/mpz.c
index d300a8e5d..8687092d0 100644
--- a/py/mpz.c
+++ b/py/mpz.c
@@ -537,83 +537,57 @@ STATIC void mpn_div(mpz_dig_t *num_dig, size_t *num_len, const mpz_dig_t *den_di
         //      not to overflow the borrow variable.  And the shifting of
         //      borrow needs some special logic (it's a shift right with
         //      round up).
-
-        if (DIG_SIZE < 8 * sizeof(mpz_dbl_dig_t) / 2) {
-            const mpz_dig_t *d = den_dig;
-            mpz_dbl_dig_t d_norm = 0;
-            mpz_dbl_dig_signed_t borrow = 0;
-
-            for (mpz_dig_t *n = num_dig - den_len; n < num_dig; ++n, ++d) {
-                d_norm = ((mpz_dbl_dig_t)*d << norm_shift) | (d_norm >> DIG_SIZE);
-                borrow += (mpz_dbl_dig_t)*n - (mpz_dbl_dig_t)quo * (d_norm & DIG_MASK); // will overflow if DIG_SIZE >= 8*sizeof(mpz_dbl_dig_t)/2
-                *n = borrow & DIG_MASK;
-                borrow >>= DIG_SIZE;
-            }
-            borrow += *num_dig; // will overflow if DIG_SIZE >= 8*sizeof(mpz_dbl_dig_t)/2
-            *num_dig = borrow & DIG_MASK;
-            borrow >>= DIG_SIZE;
-
-            // adjust quotient if it is too big
-            for (; borrow != 0; --quo) {
-                d = den_dig;
-                d_norm = 0;
-                mpz_dbl_dig_t carry = 0;
-                for (mpz_dig_t *n = num_dig - den_len; n < num_dig; ++n, ++d) {
-                    d_norm = ((mpz_dbl_dig_t)*d << norm_shift) | (d_norm >> DIG_SIZE);
-                    carry += (mpz_dbl_dig_t)*n + (d_norm & DIG_MASK);
-                    *n = carry & DIG_MASK;
-                    carry >>= DIG_SIZE;
-                }
-                carry += *num_dig;
-                *num_dig = carry & DIG_MASK;
-                carry >>= DIG_SIZE;
-
-                borrow += carry;
-            }
-        } else { // DIG_SIZE == 8 * sizeof(mpz_dbl_dig_t) / 2
-            const mpz_dig_t *d = den_dig;
-            mpz_dbl_dig_t d_norm = 0;
-            mpz_dbl_dig_t borrow = 0;
-
-            for (mpz_dig_t *n = num_dig - den_len; n < num_dig; ++n, ++d) {
-                d_norm = ((mpz_dbl_dig_t)*d << norm_shift) | (d_norm >> DIG_SIZE);
-                mpz_dbl_dig_t x = (mpz_dbl_dig_t)quo * (d_norm & DIG_MASK);
-                if (x >= *n || *n - x <= borrow) {
-                    borrow += (mpz_dbl_dig_t)x - (mpz_dbl_dig_t)*n;
-                    *n = (-borrow) & DIG_MASK;
-                    borrow = (borrow >> DIG_SIZE) + ((borrow & DIG_MASK) == 0 ? 0 : 1); // shift-right with round-up
-                } else {
-                    *n = ((mpz_dbl_dig_t)*n - (mpz_dbl_dig_t)x - (mpz_dbl_dig_t)borrow) & DIG_MASK;
-                    borrow = 0;
-                }
-            }
-            if (borrow >= *num_dig) {
-                borrow -= (mpz_dbl_dig_t)*num_dig;
-                *num_dig = (-borrow) & DIG_MASK;
+        //
+        const mpz_dig_t *d = den_dig;
+        mpz_dbl_dig_t d_norm = 0;
+        mpz_dbl_dig_t borrow = 0;
+        for (mpz_dig_t *n = num_dig - den_len; n < num_dig; ++n, ++d) {
+            d_norm = ((mpz_dbl_dig_t)*d << norm_shift) | (d_norm >> DIG_SIZE);
+            mpz_dbl_dig_t x = (mpz_dbl_dig_t)quo * (d_norm & DIG_MASK);
+            #if DIG_SIZE < MPZ_DBL_DIG_SIZE / 2
+            borrow += (mpz_dbl_dig_t)*n - x; // will overflow if DIG_SIZE >= MPZ_DBL_DIG_SIZE/2
+            *n = borrow & DIG_MASK;
+            borrow = (mpz_dbl_dig_signed_t)borrow >> DIG_SIZE;
+            #else // DIG_SIZE == MPZ_DBL_DIG_SIZE / 2
+            if (x >= *n || *n - x <= borrow) {
+                borrow += x - (mpz_dbl_dig_t)*n;
+                *n = (-borrow) & DIG_MASK;
                 borrow = (borrow >> DIG_SIZE) + ((borrow & DIG_MASK) == 0 ? 0 : 1); // shift-right with round-up
             } else {
-                *num_dig = (*num_dig - borrow) & DIG_MASK;
+                *n = ((mpz_dbl_dig_t)*n - x - borrow) & DIG_MASK;
                 borrow = 0;
             }
+            #endif
+        }
 
-            // adjust quotient if it is too big
-            for (; borrow != 0; --quo) {
-                d = den_dig;
-                d_norm = 0;
-                mpz_dbl_dig_t carry = 0;
-                for (mpz_dig_t *n = num_dig - den_len; n < num_dig; ++n, ++d) {
-                    d_norm = ((mpz_dbl_dig_t)*d << norm_shift) | (d_norm >> DIG_SIZE);
-                    carry += (mpz_dbl_dig_t)*n + (d_norm & DIG_MASK);
-                    *n = carry & DIG_MASK;
-                    carry >>= DIG_SIZE;
-                }
-                carry += (mpz_dbl_dig_t)*num_dig;
-                *num_dig = carry & DIG_MASK;
-                carry >>= DIG_SIZE;
+        #if DIG_SIZE < MPZ_DBL_DIG_SIZE / 2
+        // Borrow was negative in the above for-loop, make it positive for next if-block.
+        borrow = -borrow;
+        #endif
 
-                //assert(borrow >= carry); // enable this to check the logic
-                borrow -= carry;
+        // At this point we have either:
+        //
+        //   1. quo was the correct value and the most-sig-digit of num is exactly
+        //      cancelled by borrow (borrow == *num_dig).  In this case there is
+        //      nothing more to do.
+        //
+        //   2. quo was too large, we subtracted too many den from num, and the
+        //      most-sig-digit of num is 1 less than borrow (borrow == *num_dig + 1).
+        //      In this case we must reduce quo and add back den to num until the
+        //      carry from this operation cancels out the borrow.
+        //
+        borrow -= *num_dig;
+        for (; borrow != 0; --quo) {
+            d = den_dig;
+            d_norm = 0;
+            mpz_dbl_dig_t carry = 0;
+            for (mpz_dig_t *n = num_dig - den_len; n < num_dig; ++n, ++d) {
+                d_norm = ((mpz_dbl_dig_t)*d << norm_shift) | (d_norm >> DIG_SIZE);
+                carry += (mpz_dbl_dig_t)*n + (d_norm & DIG_MASK);
+                *n = carry & DIG_MASK;
+                carry >>= DIG_SIZE;
             }
+            borrow -= carry;
         }
 
         // store this digit of the quotient
@@ -731,17 +705,14 @@ STATIC void mpz_need_dig(mpz_t *z, size_t need) {
 }
 
 STATIC mpz_t *mpz_clone(const mpz_t *src) {
+    assert(src->alloc != 0);
     mpz_t *z = m_new_obj(mpz_t);
     z->neg = src->neg;
     z->fixed_dig = 0;
     z->alloc = src->alloc;
     z->len = src->len;
-    if (src->dig == NULL) {
-        z->dig = NULL;
-    } else {
-        z->dig = m_new(mpz_dig_t, z->alloc);
-        memcpy(z->dig, src->dig, src->alloc * sizeof(mpz_dig_t));
-    }
+    z->dig = m_new(mpz_dig_t, z->alloc);
+    memcpy(z->dig, src->dig, src->alloc * sizeof(mpz_dig_t));
     return z;
 }
 
@@ -1009,6 +980,7 @@ these functions are unused
 /* returns abs(z)
 */
 mpz_t *mpz_abs(const mpz_t *z) {
+    // TODO: handle case of z->alloc=0
     mpz_t *z2 = mpz_clone(z);
     z2->neg = 0;
     return z2;
@@ -1017,6 +989,7 @@ mpz_t *mpz_abs(const mpz_t *z) {
 /* returns -z
 */
 mpz_t *mpz_neg(const mpz_t *z) {
+    // TODO: handle case of z->alloc=0
     mpz_t *z2 = mpz_clone(z);
     z2->neg = 1 - z2->neg;
     return z2;
@@ -1390,13 +1363,14 @@ void mpz_pow_inpl(mpz_t *dest, const mpz_t *lhs, const mpz_t *rhs) {
    can have dest, lhs, rhs the same; mod can't be the same as dest
 */
 void mpz_pow3_inpl(mpz_t *dest, const mpz_t *lhs, const mpz_t *rhs, const mpz_t *mod) {
-    if (lhs->len == 0 || rhs->neg != 0) {
+    if (lhs->len == 0 || rhs->neg != 0 || (mod->len == 1 && mod->dig[0] == 1)) {
         mpz_set_from_int(dest, 0);
         return;
     }
 
+    mpz_set_from_int(dest, 1);
+
     if (rhs->len == 0) {
-        mpz_set_from_int(dest, 1);
         return;
     }
 
@@ -1404,8 +1378,6 @@ void mpz_pow3_inpl(mpz_t *dest, const mpz_t *lhs, const mpz_t *rhs, const mpz_t
     mpz_t *n = mpz_clone(rhs);
     mpz_t quo; mpz_init_zero(&quo);
 
-    mpz_set_from_int(dest, 1);
-
     while (n->len > 0) {
         if ((n->dig[0] & 1) != 0) {
             mpz_mul_inpl(dest, dest, x);
@@ -1435,6 +1407,7 @@ these functions are unused
 */
 mpz_t *mpz_gcd(const mpz_t *z1, const mpz_t *z2) {
     if (z1->len == 0) {
+        // TODO: handle case of z2->alloc=0
         mpz_t *a = mpz_clone(z2);
         a->neg = 0;
         return a;
@@ -1559,7 +1532,7 @@ mpz_t *mpz_mod(const mpz_t *lhs, const mpz_t *rhs) {
 
 // must return actual int value if it fits in mp_int_t
 mp_int_t mpz_hash(const mpz_t *z) {
-    mp_int_t val = 0;
+    mp_uint_t val = 0;
     mpz_dig_t *d = z->dig + z->len;
 
     while (d-- > z->dig) {
@@ -1674,16 +1647,12 @@ char *mpz_as_str(const mpz_t *i, unsigned int base) {
 }
 #endif
 
-// assumes enough space as calculated by mp_int_format_size
+// assumes enough space in str as calculated by mp_int_format_size
+// base must be between 2 and 32 inclusive
 // returns length of string, not including null byte
 size_t mpz_as_str_inpl(const mpz_t *i, unsigned int base, const char *prefix, char base_char, char comma, char *str) {
-    if (str == NULL) {
-        return 0;
-    }
-    if (base < 2 || base > 32) {
-        str[0] = 0;
-        return 0;
-    }
+    assert(str != NULL);
+    assert(2 <= base && base <= 32);
 
     size_t ilen = i->len;
 
diff --git a/py/mpz.h b/py/mpz.h
index e2d0c30aa..3c36cac66 100644
--- a/py/mpz.h
+++ b/py/mpz.h
@@ -55,18 +55,22 @@
 #endif
 
 #if MPZ_DIG_SIZE > 16
+#define MPZ_DBL_DIG_SIZE (64)
 typedef uint32_t mpz_dig_t;
 typedef uint64_t mpz_dbl_dig_t;
 typedef int64_t mpz_dbl_dig_signed_t;
 #elif MPZ_DIG_SIZE > 8
+#define MPZ_DBL_DIG_SIZE (32)
 typedef uint16_t mpz_dig_t;
 typedef uint32_t mpz_dbl_dig_t;
 typedef int32_t mpz_dbl_dig_signed_t;
 #elif MPZ_DIG_SIZE > 4
+#define MPZ_DBL_DIG_SIZE (16)
 typedef uint8_t mpz_dig_t;
 typedef uint16_t mpz_dbl_dig_t;
 typedef int16_t mpz_dbl_dig_signed_t;
 #else
+#define MPZ_DBL_DIG_SIZE (8)
 typedef uint8_t mpz_dig_t;
 typedef uint8_t mpz_dbl_dig_t;
 typedef int8_t mpz_dbl_dig_signed_t;
diff --git a/py/nativeglue.c b/py/nativeglue.c
index e63c2fcda..b87da6931 100644
--- a/py/nativeglue.c
+++ b/py/nativeglue.c
@@ -146,8 +146,8 @@ void *const mp_fun_table[MP_F_NUMBER_OF] = {
     mp_obj_new_dict,
     mp_obj_dict_store,
 #if MICROPY_PY_BUILTINS_SET
-    mp_obj_new_set,
     mp_obj_set_store,
+    mp_obj_new_set,
 #endif
     mp_make_function_from_raw_code,
     mp_native_call_function_n_kw,
diff --git a/py/nlr.c b/py/nlr.c
new file mode 100644
index 000000000..03d01577e
--- /dev/null
+++ b/py/nlr.c
@@ -0,0 +1,51 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2013-2017 Damien P. George
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include "py/mpstate.h"
+
+#if !MICROPY_NLR_SETJMP
+// When not using setjmp, nlr_push_tail is called from inline asm so needs special care
+#if MICROPY_NLR_X86 && MICROPY_NLR_OS_WINDOWS
+// On these 32-bit platforms make sure nlr_push_tail doesn't have a leading underscore
+unsigned int nlr_push_tail(nlr_buf_t *nlr) asm("nlr_push_tail");
+#else
+// LTO can't see inside inline asm functions so explicitly mark nlr_push_tail as used
+__attribute__((used)) unsigned int nlr_push_tail(nlr_buf_t *nlr);
+#endif
+#endif
+
+unsigned int nlr_push_tail(nlr_buf_t *nlr) {
+    nlr_buf_t **top = &MP_STATE_THREAD(nlr_top);
+    nlr->prev = *top;
+    MP_NLR_SAVE_PYSTACK(nlr);
+    *top = nlr;
+    return 0; // normal return
+}
+
+void nlr_pop(void) {
+    nlr_buf_t **top = &MP_STATE_THREAD(nlr_top);
+    *top = (*top)->prev;
+}
diff --git a/py/nlr.h b/py/nlr.h
index 8fa6eb950..90595a12d 100644
--- a/py/nlr.h
+++ b/py/nlr.h
@@ -30,30 +30,34 @@
 // exception handling, basically a stack of setjmp/longjmp buffers
 
 #include <limits.h>
-#include <setjmp.h>
 #include <assert.h>
 
 #include "py/mpconfig.h"
 
-typedef struct _nlr_buf_t nlr_buf_t;
-struct _nlr_buf_t {
-    // the entries here must all be machine word size
-    nlr_buf_t *prev;
-    void *ret_val; // always a concrete object (an exception instance)
-#if !defined(MICROPY_NLR_SETJMP) || !MICROPY_NLR_SETJMP
-#define MICROPY_NLR_SETJMP (0)
+// If MICROPY_NLR_SETJMP is not enabled then auto-detect the machine arch
+#if !MICROPY_NLR_SETJMP
+// A lot of nlr-related things need different treatment on Windows
+#if defined(_WIN32) || defined(__CYGWIN__)
+#define MICROPY_NLR_OS_WINDOWS 1
+#else
+#define MICROPY_NLR_OS_WINDOWS 0
+#endif
 #if defined(__i386__)
-    void *regs[6];
+    #define MICROPY_NLR_X86 (1)
+    #define MICROPY_NLR_NUM_REGS (6)
 #elif defined(__x86_64__)
-  #if defined(__CYGWIN__)
-    void *regs[12];
-  #else
-    void *regs[8];
-  #endif
+    #define MICROPY_NLR_X64 (1)
+    #if MICROPY_NLR_OS_WINDOWS
+        #define MICROPY_NLR_NUM_REGS (10)
+    #else
+        #define MICROPY_NLR_NUM_REGS (8)
+    #endif
 #elif defined(__thumb2__) || defined(__thumb__) || defined(__arm__)
-    void *regs[10];
+    #define MICROPY_NLR_THUMB (1)
+    #define MICROPY_NLR_NUM_REGS (10)
 #elif defined(__xtensa__)
-    void *regs[10];
+    #define MICROPY_NLR_XTENSA (1)
+    #define MICROPY_NLR_NUM_REGS (10)
 #else
     #define MICROPY_NLR_SETJMP (1)
     //#warning "No native NLR support for this arch, using setjmp implementation"
@@ -61,24 +65,58 @@ struct _nlr_buf_t {
 #endif
 
 #if MICROPY_NLR_SETJMP
-    jmp_buf jmpbuf;
+#include <setjmp.h>
 #endif
+
+typedef struct _nlr_buf_t nlr_buf_t;
+struct _nlr_buf_t {
+    // the entries here must all be machine word size
+    nlr_buf_t *prev;
+    void *ret_val; // always a concrete object (an exception instance)
+
+    #if MICROPY_NLR_SETJMP
+    jmp_buf jmpbuf;
+    #else
+    void *regs[MICROPY_NLR_NUM_REGS];
+    #endif
+
+    #if MICROPY_ENABLE_PYSTACK
+    void *pystack;
+    #endif
 };
 
-#if MICROPY_NLR_SETJMP
-#include "py/mpstate.h"
+// Helper macros to save/restore the pystack state
+#if MICROPY_ENABLE_PYSTACK
+#define MP_NLR_SAVE_PYSTACK(nlr_buf) (nlr_buf)->pystack = MP_STATE_THREAD(pystack_cur)
+#define MP_NLR_RESTORE_PYSTACK(nlr_buf) MP_STATE_THREAD(pystack_cur) = (nlr_buf)->pystack
+#else
+#define MP_NLR_SAVE_PYSTACK(nlr_buf) (void)nlr_buf
+#define MP_NLR_RESTORE_PYSTACK(nlr_buf) (void)nlr_buf
+#endif
+
+// Helper macro to use at the start of a specific nlr_jump implementation
+#define MP_NLR_JUMP_HEAD(val, top) \
+    nlr_buf_t **_top_ptr = &MP_STATE_THREAD(nlr_top); \
+    nlr_buf_t *top = *_top_ptr; \
+    if (top == NULL) { \
+        nlr_jump_fail(val); \
+    } \
+    top->ret_val = val; \
+    MP_NLR_RESTORE_PYSTACK(top); \
+    *_top_ptr = top->prev; \
 
-NORETURN void nlr_setjmp_jump(void *val);
+#if MICROPY_NLR_SETJMP
 // nlr_push() must be defined as a macro, because "The stack context will be
 // invalidated if the function which called setjmp() returns."
-#define nlr_push(buf) ((buf)->prev = MP_STATE_THREAD(nlr_top), MP_STATE_THREAD(nlr_top) = (buf), setjmp((buf)->jmpbuf))
-#define nlr_pop() { MP_STATE_THREAD(nlr_top) = MP_STATE_THREAD(nlr_top)->prev; }
-#define nlr_jump(val) nlr_setjmp_jump(val)
+// For this case it is safe to call nlr_push_tail() first.
+#define nlr_push(buf) (nlr_push_tail(buf), setjmp((buf)->jmpbuf))
 #else
 unsigned int nlr_push(nlr_buf_t *);
+#endif
+
+unsigned int nlr_push_tail(nlr_buf_t *top);
 void nlr_pop(void);
 NORETURN void nlr_jump(void *val);
-#endif
 
 // This must be implemented by a port.  It's called by nlr_jump
 // if no nlr buf has been pushed.  It must not return, but rather
@@ -107,7 +145,6 @@ NORETURN void nlr_jump_fail(void *val);
 /*
 #define nlr_push(val) \
     printf("nlr_push: before: nlr_top=%p, val=%p\n", MP_STATE_THREAD(nlr_top), val),assert(MP_STATE_THREAD(nlr_top) != val),nlr_push(val)
-#endif
 */
 #endif
 
diff --git a/py/nlrsetjmp.c b/py/nlrsetjmp.c
index 1fb459440..960dd86f5 100644
--- a/py/nlrsetjmp.c
+++ b/py/nlrsetjmp.c
@@ -3,7 +3,7 @@
  *
  * The MIT License (MIT)
  *
- * Copyright (c) 2013, 2014 Damien P. George
+ * Copyright (c) 2013-2017 Damien P. George
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -24,17 +24,18 @@
  * THE SOFTWARE.
  */
 
-#include "py/nlr.h"
+#include "py/mpstate.h"
 
 #if MICROPY_NLR_SETJMP
 
-void nlr_setjmp_jump(void *val) {
+void nlr_jump(void *val) {
     nlr_buf_t **top_ptr = &MP_STATE_THREAD(nlr_top);
     nlr_buf_t *top = *top_ptr;
     if (top == NULL) {
         nlr_jump_fail(val);
     }
     top->ret_val = val;
+    MP_NLR_RESTORE_PYSTACK(top);
     *top_ptr = top->prev;
     longjmp(top->jmpbuf, 1);
 }
diff --git a/py/nlrthumb.c b/py/nlrthumb.c
index 0616e59b0..69d3f868a 100644
--- a/py/nlrthumb.c
+++ b/py/nlrthumb.c
@@ -3,7 +3,7 @@
  *
  * The MIT License (MIT)
  *
- * Copyright (c) 2013-2016 Damien P. George
+ * Copyright (c) 2013-2017 Damien P. George
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -26,7 +26,7 @@
 
 #include "py/mpstate.h"
 
-#if (!defined(MICROPY_NLR_SETJMP) || !MICROPY_NLR_SETJMP) && (defined(__thumb2__) || defined(__thumb__) || defined(__arm__))
+#if MICROPY_NLR_THUMB
 
 #undef nlr_push
 
@@ -82,30 +82,15 @@ __attribute__((naked)) unsigned int nlr_push(nlr_buf_t *nlr) {
     : "r1", "r2", "r3"              // clobbers
                     );
 
-    return 0; // needed to silence compiler warning
+    #if !defined(__clang__) && defined(__GNUC__) && (__GNUC__ < 4 || (__GNUC__ == 4 && __GNUC_MINOR__ < 8))
+    // Older versions of gcc give an error when naked functions don't return a value
+    // Additionally exclude Clang as it also defines __GNUC__ but doesn't need this statement
+    return 0;
+    #endif
 }
 
-__attribute__((used)) unsigned int nlr_push_tail(nlr_buf_t *nlr) {
-    nlr_buf_t **top = &MP_STATE_THREAD(nlr_top);
-    nlr->prev = *top;
-    *top = nlr;
-    return 0; // normal return
-}
-
-void nlr_pop(void) {
-    nlr_buf_t **top = &MP_STATE_THREAD(nlr_top);
-    *top = (*top)->prev;
-}
-
-NORETURN __attribute__((naked)) void nlr_jump(void *val) {
-    nlr_buf_t **top_ptr = &MP_STATE_THREAD(nlr_top);
-    nlr_buf_t *top = *top_ptr;
-    if (top == NULL) {
-        nlr_jump_fail(val);
-    }
-
-    top->ret_val = val;
-    *top_ptr = top->prev;
+NORETURN void nlr_jump(void *val) {
+    MP_NLR_JUMP_HEAD(val, top)
 
     __asm volatile (
     "mov    r0, %0              \n" // r0 points to nlr_buf
@@ -142,7 +127,11 @@ NORETURN __attribute__((naked)) void nlr_jump(void *val) {
     :                               // clobbered registers
     );
 
+    #if defined(__GNUC__)
+    __builtin_unreachable();
+    #else
     for (;;); // needed to silence compiler warning
+    #endif
 }
 
-#endif // (!defined(MICROPY_NLR_SETJMP) || !MICROPY_NLR_SETJMP) && (defined(__thumb2__) || defined(__thumb__) || defined(__arm__))
+#endif // MICROPY_NLR_THUMB
diff --git a/py/nlrx64.c b/py/nlrx64.c
index 847d10398..a3a1cf341 100644
--- a/py/nlrx64.c
+++ b/py/nlrx64.c
@@ -26,25 +26,19 @@
 
 #include "py/mpstate.h"
 
-#if !MICROPY_NLR_SETJMP && defined(__x86_64__)
+#if MICROPY_NLR_X64
 
 #undef nlr_push
 
 // x86-64 callee-save registers are:
 //  rbx, rbp, rsp, r12, r13, r14, r15
 
-#if defined(_WIN32) || defined(__CYGWIN__)
-#define NLR_OS_WINDOWS 1
-#else
-#define NLR_OS_WINDOWS 0
-#endif
-
 __attribute__((used)) unsigned int nlr_push_tail(nlr_buf_t *nlr);
 
 unsigned int nlr_push(nlr_buf_t *nlr) {
     (void)nlr;
 
-    #if NLR_OS_WINDOWS
+    #if MICROPY_NLR_OS_WINDOWS
 
     __asm volatile (
     "movq   (%rsp), %rax        \n" // load return %rip
@@ -88,31 +82,12 @@ unsigned int nlr_push(nlr_buf_t *nlr) {
     return 0; // needed to silence compiler warning
 }
 
-__attribute__((used)) unsigned int nlr_push_tail(nlr_buf_t *nlr) {
-    nlr_buf_t **top = &MP_STATE_THREAD(nlr_top);
-    nlr->prev = *top;
-    *top = nlr;
-    return 0; // normal return
-}
-
-void nlr_pop(void) {
-    nlr_buf_t **top = &MP_STATE_THREAD(nlr_top);
-    *top = (*top)->prev;
-}
-
 NORETURN void nlr_jump(void *val) {
-    nlr_buf_t **top_ptr = &MP_STATE_THREAD(nlr_top);
-    nlr_buf_t *top = *top_ptr;
-    if (top == NULL) {
-        nlr_jump_fail(val);
-    }
-
-    top->ret_val = val;
-    *top_ptr = top->prev;
+    MP_NLR_JUMP_HEAD(val, top)
 
     __asm volatile (
     "movq   %0, %%rcx           \n" // %rcx points to nlr_buf
-    #if NLR_OS_WINDOWS
+    #if MICROPY_NLR_OS_WINDOWS
     "movq   88(%%rcx), %%rsi    \n" // load saved %rsi
     "movq   80(%%rcx), %%rdi    \n" // load saved %rdr
     #endif
@@ -136,4 +111,4 @@ NORETURN void nlr_jump(void *val) {
     for (;;); // needed to silence compiler warning
 }
 
-#endif // !MICROPY_NLR_SETJMP && defined(__x86_64__)
+#endif // MICROPY_NLR_X64
diff --git a/py/nlrx86.c b/py/nlrx86.c
index 094dea3cc..59b97d8ee 100644
--- a/py/nlrx86.c
+++ b/py/nlrx86.c
@@ -26,34 +26,42 @@
 
 #include "py/mpstate.h"
 
-#if !MICROPY_NLR_SETJMP && defined(__i386__)
+#if MICROPY_NLR_X86
 
 #undef nlr_push
 
 // For reference, x86 callee save regs are:
 //  ebx, esi, edi, ebp, esp, eip
 
-#if defined(_WIN32) || defined(__CYGWIN__)
-#define NLR_OS_WINDOWS 1
+#if MICROPY_NLR_OS_WINDOWS
+unsigned int nlr_push_tail(nlr_buf_t *nlr) asm("nlr_push_tail");
 #else
-#define NLR_OS_WINDOWS 0
+__attribute__((used)) unsigned int nlr_push_tail(nlr_buf_t *nlr);
 #endif
 
-#if NLR_OS_WINDOWS
-unsigned int nlr_push_tail(nlr_buf_t *nlr) asm("nlr_push_tail");
+#if !defined(__clang__) && defined(__GNUC__) && __GNUC__ >= 8
+// Since gcc 8.0 the naked attribute is supported
+#define USE_NAKED (1)
+#define UNDO_PRELUDE (0)
+#elif defined(__ZEPHYR__) || defined(__ANDROID__)
+// Zephyr and Android use a different calling convention by default
+#define USE_NAKED (0)
+#define UNDO_PRELUDE (0)
 #else
-__attribute__((used)) unsigned int nlr_push_tail(nlr_buf_t *nlr);
+#define USE_NAKED (0)
+#define UNDO_PRELUDE (1)
 #endif
 
+#if USE_NAKED
+__attribute__((naked))
+#endif
 unsigned int nlr_push(nlr_buf_t *nlr) {
+    #if !USE_NAKED
     (void)nlr;
+    #endif
 
     __asm volatile (
-    // Check for Zephyr, which uses a different calling convention
-    // by default.
-    // TODE: Better support for various x86 calling conventions
-    // (unfortunately, __attribute__((naked)) is not supported on x86).
-    #if !(defined(__ZEPHYR__) || defined(__ANDROID__))
+    #if UNDO_PRELUDE
     "pop    %ebp                \n" // undo function's prelude
     #endif
     "mov    4(%esp), %edx       \n" // load nlr_buf
@@ -67,30 +75,13 @@ unsigned int nlr_push(nlr_buf_t *nlr) {
     "jmp    nlr_push_tail       \n" // do the rest in C
     );
 
+    #if !USE_NAKED
     return 0; // needed to silence compiler warning
-}
-
-__attribute__((used)) unsigned int nlr_push_tail(nlr_buf_t *nlr) {
-    nlr_buf_t **top = &MP_STATE_THREAD(nlr_top);
-    nlr->prev = *top;
-    *top = nlr;
-    return 0; // normal return
-}
-
-void nlr_pop(void) {
-    nlr_buf_t **top = &MP_STATE_THREAD(nlr_top);
-    *top = (*top)->prev;
+    #endif
 }
 
 NORETURN void nlr_jump(void *val) {
-    nlr_buf_t **top_ptr = &MP_STATE_THREAD(nlr_top);
-    nlr_buf_t *top = *top_ptr;
-    if (top == NULL) {
-        nlr_jump_fail(val);
-    }
-
-    top->ret_val = val;
-    *top_ptr = top->prev;
+    MP_NLR_JUMP_HEAD(val, top)
 
     __asm volatile (
     "mov    %0, %%edx           \n" // %edx points to nlr_buf
@@ -112,4 +103,4 @@ NORETURN void nlr_jump(void *val) {
     for (;;); // needed to silence compiler warning
 }
 
-#endif // !MICROPY_NLR_SETJMP && defined(__i386__)
+#endif // MICROPY_NLR_X86
diff --git a/py/nlrxtensa.c b/py/nlrxtensa.c
index 4520e7e7a..cd3dee364 100644
--- a/py/nlrxtensa.c
+++ b/py/nlrxtensa.c
@@ -26,7 +26,7 @@
 
 #include "py/mpstate.h"
 
-#if !MICROPY_NLR_SETJMP && defined(__xtensa__)
+#if MICROPY_NLR_XTENSA
 
 #undef nlr_push
 
@@ -55,27 +55,8 @@ unsigned int nlr_push(nlr_buf_t *nlr) {
     return 0; // needed to silence compiler warning
 }
 
-__attribute__((used)) unsigned int nlr_push_tail(nlr_buf_t *nlr) {
-    nlr_buf_t **top = &MP_STATE_THREAD(nlr_top);
-    nlr->prev = *top;
-    *top = nlr;
-    return 0; // normal return
-}
-
-void nlr_pop(void) {
-    nlr_buf_t **top = &MP_STATE_THREAD(nlr_top);
-    *top = (*top)->prev;
-}
-
 NORETURN void nlr_jump(void *val) {
-    nlr_buf_t **top_ptr = &MP_STATE_THREAD(nlr_top);
-    nlr_buf_t *top = *top_ptr;
-    if (top == NULL) {
-        nlr_jump_fail(val);
-    }
-
-    top->ret_val = val;
-    *top_ptr = top->prev;
+    MP_NLR_JUMP_HEAD(val, top)
 
     __asm volatile (
     "mov.n   a2, %0             \n" // a2 points to nlr_buf
@@ -99,4 +80,4 @@ NORETURN void nlr_jump(void *val) {
     for (;;); // needed to silence compiler warning
 }
 
-#endif // !MICROPY_NLR_SETJMP && defined(__xtensa__)
+#endif // MICROPY_NLR_XTENSA
diff --git a/py/obj.h b/py/obj.h
index d086d3c14..42c88ef67 100644
--- a/py/obj.h
+++ b/py/obj.h
@@ -172,8 +172,8 @@ static inline bool MP_OBJ_IS_OBJ(mp_const_obj_t o)
 
 static inline bool MP_OBJ_IS_SMALL_INT(mp_const_obj_t o)
     { return ((((mp_int_t)(o)) & 0xffff000000000000) == 0x0001000000000000); }
-#define MP_OBJ_SMALL_INT_VALUE(o) (((intptr_t)(o)) >> 1)
-#define MP_OBJ_NEW_SMALL_INT(small_int) ((mp_obj_t)(((uintptr_t)(small_int)) << 1) | 0x0001000000000001)
+#define MP_OBJ_SMALL_INT_VALUE(o) (((mp_int_t)((o) << 16)) >> 17)
+#define MP_OBJ_NEW_SMALL_INT(small_int) (((((uint64_t)(small_int)) & 0x7fffffffffff) << 1) | 0x0001000000000001)
 
 static inline bool MP_OBJ_IS_QSTR(mp_const_obj_t o)
     { return ((((mp_int_t)(o)) & 0xffff000000000000) == 0x0002000000000000); }
@@ -181,7 +181,7 @@ static inline bool MP_OBJ_IS_QSTR(mp_const_obj_t o)
 #define MP_OBJ_NEW_QSTR(qst) ((mp_obj_t)((((mp_uint_t)(qst)) << 1) | 0x0002000000000001))
 
 #if MICROPY_PY_BUILTINS_FLOAT
-#define mp_const_float_e {((mp_obj_t)((uint64_t)0x4005bf0a8b125769 + 0x8004000000000000))}
+#define mp_const_float_e {((mp_obj_t)((uint64_t)0x4005bf0a8b145769 + 0x8004000000000000))}
 #define mp_const_float_pi {((mp_obj_t)((uint64_t)0x400921fb54442d18 + 0x8004000000000000))}
 
 static inline bool mp_obj_is_float(mp_const_obj_t o) {
@@ -252,6 +252,8 @@ typedef struct _mp_rom_obj_t { mp_const_obj_t o; } mp_rom_obj_t;
 
 // The macros below are derived from the ones above and are used to
 // check for more specific object types.
+// Note: these are kept as macros because inline functions sometimes use much
+// more code space than the equivalent macros, depending on the compiler.
 
 #define MP_OBJ_IS_TYPE(o, t) (MP_OBJ_IS_OBJ(o) && (((mp_obj_base_t*)MP_OBJ_TO_PTR(o))->type == (t))) // this does not work for checking int, str or fun; use below macros for that
 #define MP_OBJ_IS_INT(o) (MP_OBJ_IS_SMALL_INT(o) || MP_OBJ_IS_TYPE(o, &mp_type_int))
@@ -259,17 +261,6 @@ typedef struct _mp_rom_obj_t { mp_const_obj_t o; } mp_rom_obj_t;
 #define MP_OBJ_IS_STR_OR_BYTES(o) (MP_OBJ_IS_QSTR(o) || (MP_OBJ_IS_OBJ(o) && ((mp_obj_base_t*)MP_OBJ_TO_PTR(o))->type->binary_op == mp_obj_str_binary_op))
 #define MP_OBJ_IS_FUN(o) (MP_OBJ_IS_OBJ(o) && (((mp_obj_base_t*)MP_OBJ_TO_PTR(o))->type->name == MP_QSTR_function))
 
-// Note: inline functions sometimes use much more code space than the
-// equivalent macros, depending on the compiler.
-//static inline bool MP_OBJ_IS_TYPE(mp_const_obj_t o, const mp_obj_type_t *t) { return (MP_OBJ_IS_OBJ(o) && (((mp_obj_base_t*)(o))->type == (t))); } // this does not work for checking a string, use below macro for that
-//static inline bool MP_OBJ_IS_INT(mp_const_obj_t o) { return (MP_OBJ_IS_SMALL_INT(o) || MP_OBJ_IS_TYPE(o, &mp_type_int)); } // returns true if o is a small int or long int
-// Need to forward declare these for the inline function to compile.
-extern const mp_obj_type_t mp_type_int;
-extern const mp_obj_type_t mp_type_bool;
-static inline bool mp_obj_is_integer(mp_const_obj_t o) { return MP_OBJ_IS_INT(o) || MP_OBJ_IS_TYPE(o, &mp_type_bool); } // returns true if o is bool, small int or long int
-//static inline bool MP_OBJ_IS_STR(mp_const_obj_t o) { return (MP_OBJ_IS_QSTR(o) || MP_OBJ_IS_TYPE(o, &mp_type_str)); }
-
-
 // These macros are used to declare and define constant function objects
 // You can put "static" in front of the definitions to make them local
 
@@ -462,22 +453,15 @@ typedef struct _mp_buffer_p_t {
 bool mp_get_buffer(mp_obj_t obj, mp_buffer_info_t *bufinfo, mp_uint_t flags);
 void mp_get_buffer_raise(mp_obj_t obj, mp_buffer_info_t *bufinfo, mp_uint_t flags);
 
-// Stream protocol
-typedef struct _mp_stream_p_t {
-    // On error, functions should return MP_STREAM_ERROR and fill in *errcode (values
-    // are implementation-dependent, but will be exposed to user, e.g. via exception).
-    mp_uint_t (*read)(mp_obj_t obj, void *buf, mp_uint_t size, int *errcode);
-    mp_uint_t (*write)(mp_obj_t obj, const void *buf, mp_uint_t size, int *errcode);
-    mp_uint_t (*ioctl)(mp_obj_t obj, mp_uint_t request, uintptr_t arg, int *errcode);
-    mp_uint_t is_text : 1; // default is bytes, set this for text stream
-} mp_stream_p_t;
-
 struct _mp_obj_type_t {
     // A type is an object so must start with this entry, which points to mp_type_type.
     mp_obj_base_t base;
 
-    // The name of this type.
-    qstr name;
+    // Flags associated with this type.
+    uint16_t flags;
+
+    // The name of this type, a qstr.
+    uint16_t name;
 
     // Corresponds to __repr__ and __str__ special methods.
     mp_print_fun_t print;
@@ -553,6 +537,7 @@ extern const mp_obj_type_t mp_type_list;
 extern const mp_obj_type_t mp_type_map; // map (the python builtin, not the dict implementation detail)
 extern const mp_obj_type_t mp_type_enumerate;
 extern const mp_obj_type_t mp_type_filter;
+extern const mp_obj_type_t mp_type_deque;
 extern const mp_obj_type_t mp_type_dict;
 extern const mp_obj_type_t mp_type_ordereddict;
 extern const mp_obj_type_t mp_type_range;
@@ -625,7 +610,6 @@ extern const struct _mp_obj_str_t mp_const_empty_bytes_obj;
 extern const struct _mp_obj_tuple_t mp_const_empty_tuple_obj;
 extern const struct _mp_obj_singleton_t mp_const_ellipsis_obj;
 extern const struct _mp_obj_singleton_t mp_const_notimplemented_obj;
-extern const struct _mp_obj_exception_t mp_const_MemoryError_obj;
 extern const struct _mp_obj_exception_t mp_const_GeneratorExit_obj;
 
 // General API for objects
@@ -638,7 +622,8 @@ mp_obj_t mp_obj_new_int_from_uint(mp_uint_t value);
 mp_obj_t mp_obj_new_int_from_str_len(const char **str, size_t len, bool neg, unsigned int base);
 mp_obj_t mp_obj_new_int_from_ll(long long val); // this must return a multi-precision integer object (or raise an overflow exception)
 mp_obj_t mp_obj_new_int_from_ull(unsigned long long val); // this must return a multi-precision integer object (or raise an overflow exception)
-mp_obj_t mp_obj_new_str(const char* data, size_t len, bool make_qstr_if_not_already);
+mp_obj_t mp_obj_new_str(const char* data, size_t len);
+mp_obj_t mp_obj_new_str_via_qstr(const char* data, size_t len);
 mp_obj_t mp_obj_new_str_from_vstr(const mp_obj_type_t *type, vstr_t *vstr);
 mp_obj_t mp_obj_new_bytes(const byte* data, size_t len);
 mp_obj_t mp_obj_new_bytearray(size_t n, void *items);
@@ -682,6 +667,7 @@ bool mp_obj_is_true(mp_obj_t arg);
 bool mp_obj_is_callable(mp_obj_t o_in);
 bool mp_obj_equal(mp_obj_t o1, mp_obj_t o2);
 
+static inline bool mp_obj_is_integer(mp_const_obj_t o) { return MP_OBJ_IS_INT(o) || MP_OBJ_IS_TYPE(o, &mp_type_bool); } // returns true if o is bool, small int or long int
 mp_int_t mp_obj_get_int(mp_const_obj_t arg);
 mp_int_t mp_obj_get_int_truncated(mp_const_obj_t arg);
 bool mp_obj_get_int_maybe(mp_const_obj_t arg, mp_int_t *value);
@@ -729,6 +715,7 @@ qstr mp_obj_str_get_qstr(mp_obj_t self_in); // use this if you will anyway conve
 const char *mp_obj_str_get_str(mp_obj_t self_in); // use this only if you need the string to be null terminated
 const char *mp_obj_str_get_data(mp_obj_t self_in, size_t *len);
 mp_obj_t mp_obj_str_intern(mp_obj_t str);
+mp_obj_t mp_obj_str_intern_checked(mp_obj_t obj);
 void mp_str_print_quoted(const mp_print_t *print, const byte *str_data, size_t str_len, bool is_bytes);
 
 #if MICROPY_PY_BUILTINS_FLOAT
@@ -753,8 +740,6 @@ void mp_obj_tuple_del(mp_obj_t self_in);
 mp_int_t mp_obj_tuple_hash(mp_obj_t self_in);
 
 // list
-struct _mp_obj_list_t;
-void mp_obj_list_init(struct _mp_obj_list_t *o, size_t n);
 mp_obj_t mp_obj_list_append(mp_obj_t self_in, mp_obj_t arg);
 mp_obj_t mp_obj_list_remove(mp_obj_t self_in, mp_obj_t value);
 void mp_obj_list_get(mp_obj_t self_in, size_t *len, mp_obj_t **items);
diff --git a/py/objarray.c b/py/objarray.c
index c4c547e19..94f887857 100644
--- a/py/objarray.c
+++ b/py/objarray.c
@@ -222,7 +222,7 @@ STATIC mp_obj_t memoryview_make_new(const mp_obj_type_t *type_in, size_t n_args,
 
     // test if the object can be written to
     if (mp_get_buffer(args[0], &bufinfo, MP_BUFFER_RW)) {
-        self->typecode |= 0x80; // used to indicate writable buffer
+        self->typecode |= MP_OBJ_ARRAY_TYPECODE_FLAG_RW; // indicate writable buffer
     }
 
     return MP_OBJ_FROM_PTR(self);
@@ -302,8 +302,7 @@ STATIC mp_obj_t array_binary_op(mp_binary_op_t op, mp_obj_t lhs_in, mp_obj_t rhs
             return lhs_in;
         }
 
-        case MP_BINARY_OP_IN: {
-            /* NOTE `a in b` is `b.__contains__(a)` */
+        case MP_BINARY_OP_CONTAINS: {
             mp_buffer_info_t lhs_bufinfo;
             mp_buffer_info_t rhs_bufinfo;
 
@@ -448,7 +447,7 @@ STATIC mp_obj_t array_subscr(mp_obj_t self_in, mp_obj_t index_in, mp_obj_t value
                 uint8_t* dest_items = o->items;
                 #if MICROPY_PY_BUILTINS_MEMORYVIEW
                 if (o->base.type == &mp_type_memoryview) {
-                    if ((o->typecode & 0x80) == 0) {
+                    if (!(o->typecode & MP_OBJ_ARRAY_TYPECODE_FLAG_RW)) {
                         // store to read-only memoryview not allowed
                         return MP_OBJ_NULL;
                     }
@@ -507,7 +506,7 @@ STATIC mp_obj_t array_subscr(mp_obj_t self_in, mp_obj_t index_in, mp_obj_t value
             #if MICROPY_PY_BUILTINS_MEMORYVIEW
             if (o->base.type == &mp_type_memoryview) {
                 index += o->free;
-                if (value != MP_OBJ_SENTINEL && (o->typecode & 0x80) == 0) {
+                if (value != MP_OBJ_SENTINEL && !(o->typecode & MP_OBJ_ARRAY_TYPECODE_FLAG_RW)) {
                     // store to read-only memoryview
                     return MP_OBJ_NULL;
                 }
@@ -533,7 +532,7 @@ STATIC mp_int_t array_get_buffer(mp_obj_t o_in, mp_buffer_info_t *bufinfo, mp_ui
     bufinfo->typecode = o->typecode & TYPECODE_MASK;
     #if MICROPY_PY_BUILTINS_MEMORYVIEW
     if (o->base.type == &mp_type_memoryview) {
-        if ((o->typecode & 0x80) == 0 && (flags & MP_BUFFER_WRITE)) {
+        if (!(o->typecode & MP_OBJ_ARRAY_TYPECODE_FLAG_RW) && (flags & MP_BUFFER_WRITE)) {
             // read-only memoryview
             return 1;
         }
diff --git a/py/objarray.h b/py/objarray.h
index 038966845..0dad70571 100644
--- a/py/objarray.h
+++ b/py/objarray.h
@@ -29,6 +29,9 @@
 
 #include "py/obj.h"
 
+// Used only for memoryview types, set in "typecode" to indicate a writable memoryview
+#define MP_OBJ_ARRAY_TYPECODE_FLAG_RW (0x80)
+
 typedef struct _mp_obj_array_t {
     mp_obj_base_t base;
     size_t typecode : 8;
diff --git a/py/objboundmeth.c b/py/objboundmeth.c
index 890f8b15b..b0df6a68a 100644
--- a/py/objboundmeth.c
+++ b/py/objboundmeth.c
@@ -51,6 +51,9 @@ mp_obj_t mp_call_method_self_n_kw(mp_obj_t meth, mp_obj_t self, size_t n_args, s
     // need to insert self before all other args and then call meth
     size_t n_total = n_args + 2 * n_kw;
     mp_obj_t *args2 = NULL;
+    #if MICROPY_ENABLE_PYSTACK
+    args2 = mp_pystack_alloc(sizeof(mp_obj_t) * (1 + n_total));
+    #else
     mp_obj_t *free_args2 = NULL;
     if (n_total > 4) {
         // try to use heap to allocate temporary args array
@@ -61,12 +64,17 @@ mp_obj_t mp_call_method_self_n_kw(mp_obj_t meth, mp_obj_t self, size_t n_args, s
         // (fallback to) use stack to allocate temporary args array
         args2 = alloca(sizeof(mp_obj_t) * (1 + n_total));
     }
+    #endif
     args2[0] = self;
     memcpy(args2 + 1, args, n_total * sizeof(mp_obj_t));
     mp_obj_t res = mp_call_function_n_kw(meth, n_args + 1, n_kw, args2);
+    #if MICROPY_ENABLE_PYSTACK
+    mp_pystack_free(args2);
+    #else
     if (free_args2 != NULL) {
         m_del(mp_obj_t, free_args2, 1 + n_total);
     }
+    #endif
     return res;
 }
 
diff --git a/py/objdeque.c b/py/objdeque.c
new file mode 100644
index 000000000..1cff1f8d3
--- /dev/null
+++ b/py/objdeque.c
@@ -0,0 +1,167 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2018 Paul Sokolovsky
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include <unistd.h> // for ssize_t
+#include <string.h>
+
+#include "py/mpconfig.h"
+#if MICROPY_PY_COLLECTIONS_DEQUE
+
+#include "py/runtime.h"
+
+typedef struct _mp_obj_deque_t {
+    mp_obj_base_t base;
+    size_t alloc;
+    size_t i_get;
+    size_t i_put;
+    mp_obj_t *items;
+    uint32_t flags;
+    #define FLAG_CHECK_OVERFLOW 1
+} mp_obj_deque_t;
+
+STATIC mp_obj_t deque_make_new(const mp_obj_type_t *type, size_t n_args, size_t n_kw, const mp_obj_t *args) {
+    mp_arg_check_num(n_args, n_kw, 2, 3, false);
+
+    /* Initialization from existing sequence is not supported, so an empty
+       tuple must be passed as such. */
+    if (args[0] != mp_const_empty_tuple) {
+        mp_raise_ValueError(NULL);
+    }
+
+    // Protect against -1 leading to zero-length allocation and bad array access
+    mp_int_t maxlen = mp_obj_get_int(args[1]);
+    if (maxlen < 0) {
+        mp_raise_ValueError(NULL);
+    }
+
+    mp_obj_deque_t *o = m_new_obj(mp_obj_deque_t);
+    o->base.type = type;
+    o->alloc = maxlen + 1;
+    o->i_get = o->i_put = 0;
+    o->items = m_new0(mp_obj_t, o->alloc);
+
+    if (n_args > 2) {
+        o->flags = mp_obj_get_int(args[2]);
+    }
+
+    return MP_OBJ_FROM_PTR(o);
+}
+
+STATIC mp_obj_t deque_unary_op(mp_unary_op_t op, mp_obj_t self_in) {
+    mp_obj_deque_t *self = MP_OBJ_TO_PTR(self_in);
+    switch (op) {
+        case MP_UNARY_OP_BOOL:
+            return mp_obj_new_bool(self->i_get != self->i_put);
+        case MP_UNARY_OP_LEN: {
+            ssize_t len = self->i_put - self->i_get;
+            if (len < 0) {
+                len += self->alloc;
+            }
+            return MP_OBJ_NEW_SMALL_INT(len);
+        }
+        #if MICROPY_PY_SYS_GETSIZEOF
+        case MP_UNARY_OP_SIZEOF: {
+            size_t sz = sizeof(*self) + sizeof(mp_obj_t) * self->alloc;
+            return MP_OBJ_NEW_SMALL_INT(sz);
+        }
+        #endif
+        default:
+            return MP_OBJ_NULL; // op not supported
+    }
+}
+
+STATIC mp_obj_t mp_obj_deque_append(mp_obj_t self_in, mp_obj_t arg) {
+    mp_obj_deque_t *self = MP_OBJ_TO_PTR(self_in);
+
+    size_t new_i_put = self->i_put + 1;
+    if (new_i_put == self->alloc) {
+        new_i_put = 0;
+    }
+
+    if (self->flags & FLAG_CHECK_OVERFLOW && new_i_put == self->i_get) {
+        mp_raise_msg(&mp_type_IndexError, "full");
+    }
+
+    self->items[self->i_put] = arg;
+    self->i_put = new_i_put;
+
+    if (self->i_get == new_i_put) {
+        if (++self->i_get == self->alloc) {
+            self->i_get = 0;
+        }
+    }
+
+    return mp_const_none;
+}
+STATIC MP_DEFINE_CONST_FUN_OBJ_2(deque_append_obj, mp_obj_deque_append);
+
+STATIC mp_obj_t deque_popleft(mp_obj_t self_in) {
+    mp_obj_deque_t *self = MP_OBJ_TO_PTR(self_in);
+
+    if (self->i_get == self->i_put) {
+        mp_raise_msg(&mp_type_IndexError, "empty");
+    }
+
+    mp_obj_t ret = self->items[self->i_get];
+    self->items[self->i_get] = MP_OBJ_NULL;
+
+    if (++self->i_get == self->alloc) {
+        self->i_get = 0;
+    }
+
+    return ret;
+}
+STATIC MP_DEFINE_CONST_FUN_OBJ_1(deque_popleft_obj, deque_popleft);
+
+#if 0
+STATIC mp_obj_t deque_clear(mp_obj_t self_in) {
+    mp_obj_deque_t *self = MP_OBJ_TO_PTR(self_in);
+    self->i_get = self->i_put = 0;
+    mp_seq_clear(self->items, 0, self->alloc, sizeof(*self->items));
+    return mp_const_none;
+}
+STATIC MP_DEFINE_CONST_FUN_OBJ_1(deque_clear_obj, deque_clear);
+#endif
+
+STATIC const mp_rom_map_elem_t deque_locals_dict_table[] = {
+    { MP_ROM_QSTR(MP_QSTR_append), MP_ROM_PTR(&deque_append_obj) },
+    #if 0
+    { MP_ROM_QSTR(MP_QSTR_clear), MP_ROM_PTR(&deque_clear_obj) },
+    #endif
+    { MP_ROM_QSTR(MP_QSTR_popleft), MP_ROM_PTR(&deque_popleft_obj) },
+};
+
+STATIC MP_DEFINE_CONST_DICT(deque_locals_dict, deque_locals_dict_table);
+
+const mp_obj_type_t mp_type_deque = {
+    { &mp_type_type },
+    .name = MP_QSTR_deque,
+    .make_new = deque_make_new,
+    .unary_op = deque_unary_op,
+    .locals_dict = (mp_obj_dict_t*)&deque_locals_dict,
+};
+
+#endif // MICROPY_PY_COLLECTIONS_DEQUE
diff --git a/py/objdict.c b/py/objdict.c
index 1553a83b4..c0647067a 100644
--- a/py/objdict.c
+++ b/py/objdict.c
@@ -115,7 +115,7 @@ STATIC mp_obj_t dict_unary_op(mp_unary_op_t op, mp_obj_t self_in) {
 STATIC mp_obj_t dict_binary_op(mp_binary_op_t op, mp_obj_t lhs_in, mp_obj_t rhs_in) {
     mp_obj_dict_t *o = MP_OBJ_TO_PTR(lhs_in);
     switch (op) {
-        case MP_BINARY_OP_IN: {
+        case MP_BINARY_OP_CONTAINS: {
             mp_map_elem_t *elem = mp_map_lookup(&o->map, rhs_in, MP_MAP_LOOKUP);
             return mp_obj_new_bool(elem != NULL);
         }
@@ -193,42 +193,18 @@ STATIC mp_obj_t dict_subscr(mp_obj_t self_in, mp_obj_t index, mp_obj_t value) {
 }
 
 /******************************************************************************/
-/* dict iterator                                                              */
-
-typedef struct _mp_obj_dict_it_t {
-    mp_obj_base_t base;
-    mp_fun_1_t iternext;
-    mp_obj_t dict;
-    size_t cur;
-} mp_obj_dict_it_t;
-
-STATIC mp_obj_t dict_it_iternext(mp_obj_t self_in) {
-    mp_obj_dict_it_t *self = MP_OBJ_TO_PTR(self_in);
-    mp_map_elem_t *next = dict_iter_next(MP_OBJ_TO_PTR(self->dict), &self->cur);
+/* dict methods                                                               */
 
-    if (next == NULL) {
-        return MP_OBJ_STOP_ITERATION;
-    } else {
-        return next->key;
+STATIC void mp_ensure_not_fixed(const mp_obj_dict_t *dict) {
+    if (dict->map.is_fixed) {
+        mp_raise_TypeError(NULL);
     }
 }
 
-STATIC mp_obj_t dict_getiter(mp_obj_t self_in, mp_obj_iter_buf_t *iter_buf) {
-    assert(sizeof(mp_obj_dict_it_t) <= sizeof(mp_obj_iter_buf_t));
-    mp_obj_dict_it_t *o = (mp_obj_dict_it_t*)iter_buf;
-    o->base.type = &mp_type_polymorph_iter;
-    o->iternext = dict_it_iternext;
-    o->dict = self_in;
-    o->cur = 0;
-    return MP_OBJ_FROM_PTR(o);
-}
-
-/******************************************************************************/
-/* dict methods                                                               */
-
 STATIC mp_obj_t dict_clear(mp_obj_t self_in) {
     mp_check_self(MP_OBJ_IS_DICT_TYPE(self_in));
     mp_obj_dict_t *self = MP_OBJ_TO_PTR(self_in);
+    mp_ensure_not_fixed(self);
 
     mp_map_clear(&self->map);
 
@@ -284,6 +260,9 @@ STATIC MP_DEFINE_CONST_CLASSMETHOD_OBJ(dict_fromkeys_obj, MP_ROM_PTR(&dict_fromk
 STATIC mp_obj_t dict_get_helper(size_t n_args, const mp_obj_t *args, mp_map_lookup_kind_t lookup_kind) {
     mp_check_self(MP_OBJ_IS_DICT_TYPE(args[0]));
     mp_obj_dict_t *self = MP_OBJ_TO_PTR(args[0]);
+    if (lookup_kind != MP_MAP_LOOKUP) {
+        mp_ensure_not_fixed(self);
+    }
     mp_map_elem_t *elem = mp_map_lookup(&self->map, args[1], lookup_kind);
     mp_obj_t value;
     if (elem == NULL || elem->value == MP_OBJ_NULL) {
@@ -326,6 +305,7 @@ STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(dict_setdefault_obj, 2, 3, dict_setde
 STATIC mp_obj_t dict_popitem(mp_obj_t self_in) {
     mp_check_self(MP_OBJ_IS_DICT_TYPE(self_in));
     mp_obj_dict_t *self = MP_OBJ_TO_PTR(self_in);
+    mp_ensure_not_fixed(self);
     size_t cur = 0;
     mp_map_elem_t *next = dict_iter_next(self, &cur);
     if (next == NULL) {
@@ -344,6 +324,7 @@ STATIC MP_DEFINE_CONST_FUN_OBJ_1(dict_popitem_obj, dict_popitem);
 STATIC mp_obj_t dict_update(size_t n_args, const mp_obj_t *args, mp_map_t *kwargs) {
     mp_check_self(MP_OBJ_IS_DICT_TYPE(args[0]));
     mp_obj_dict_t *self = MP_OBJ_TO_PTR(args[0]);
+    mp_ensure_not_fixed(self);
 
     mp_arg_check_num(n_args, kwargs->used, 1, 2, true);
 
@@ -485,7 +466,7 @@ STATIC mp_obj_t dict_view_binary_op(mp_binary_op_t op, mp_obj_t lhs_in, mp_obj_t
     if (o->kind != MP_DICT_VIEW_KEYS) {
         return MP_OBJ_NULL; // op not supported
     }
-    if (op != MP_BINARY_OP_IN) {
+    if (op != MP_BINARY_OP_CONTAINS) {
         return MP_OBJ_NULL; // op not supported
     }
     return dict_binary_op(op, o->dict, rhs_in);
@@ -528,6 +509,20 @@ STATIC mp_obj_t dict_values(mp_obj_t self_in) {
 STATIC MP_DEFINE_CONST_FUN_OBJ_1(dict_values_obj, dict_values);
 
 /******************************************************************************/
+/* dict iterator                                                              */
+
+STATIC mp_obj_t dict_getiter(mp_obj_t self_in, mp_obj_iter_buf_t *iter_buf) {
+    assert(sizeof(mp_obj_dict_view_it_t) <= sizeof(mp_obj_iter_buf_t));
+    mp_check_self(MP_OBJ_IS_DICT_TYPE(self_in));
+    mp_obj_dict_view_it_t *o = (mp_obj_dict_view_it_t*)iter_buf;
+    o->base.type = &dict_view_it_type;
+    o->kind = MP_DICT_VIEW_KEYS;
+    o->dict = self_in;
+    o->cur = 0;
+    return MP_OBJ_FROM_PTR(o);
+}
+
+/******************************************************************************/
 /* dict constructors & public C API                                           */
 
 STATIC const mp_rom_map_elem_t dict_locals_dict_table[] = {
@@ -595,6 +590,7 @@ size_t mp_obj_dict_len(mp_obj_t self_in) {
 mp_obj_t mp_obj_dict_store(mp_obj_t self_in, mp_obj_t key, mp_obj_t value) {
     mp_check_self(MP_OBJ_IS_DICT_TYPE(self_in));
     mp_obj_dict_t *self = MP_OBJ_TO_PTR(self_in);
+    mp_ensure_not_fixed(self);
     mp_map_lookup(&self->map, key, MP_MAP_LOOKUP_ADD_IF_NOT_FOUND)->value = value;
     return self_in;
 }
diff --git a/py/objexcept.c b/py/objexcept.c
index f0874df77..5b5650c5f 100644
--- a/py/objexcept.c
+++ b/py/objexcept.c
@@ -43,9 +43,6 @@
 // Number of traceback entries to reserve in the emergency exception buffer
 #define EMG_TRACEBACK_ALLOC (2 * TRACEBACK_ENTRY_LEN)
 
-// Instance of MemoryError exception - needed by mp_malloc_fail
-const mp_obj_exception_t mp_const_MemoryError_obj = {{&mp_type_MemoryError}, 0, 0, NULL, (mp_obj_tuple_t*)&mp_const_empty_tuple_obj};
-
 // Optionally allocated buffer for storing the first argument of an exception
 // allocated when the heap is locked.
 #if MICROPY_ENABLE_EMERGENCY_EXCEPTION_BUF
@@ -96,7 +93,7 @@ mp_obj_t mp_alloc_emergency_exception_buf(mp_obj_t size_in) {
 // definition module-private so far, have it here.
 const mp_obj_exception_t mp_const_GeneratorExit_obj = {{&mp_type_GeneratorExit}, 0, 0, NULL, (mp_obj_tuple_t*)&mp_const_empty_tuple_obj};
 
-STATIC void mp_obj_exception_print(const mp_print_t *print, mp_obj_t o_in, mp_print_kind_t kind) {
+void mp_obj_exception_print(const mp_print_t *print, mp_obj_t o_in, mp_print_kind_t kind) {
     mp_obj_exception_t *o = MP_OBJ_TO_PTR(o_in);
     mp_print_kind_t k = kind & ~PRINT_EXC_SUBCLASS;
     bool is_subclass = kind & PRINT_EXC_SUBCLASS;
@@ -117,7 +114,7 @@ STATIC void mp_obj_exception_print(const mp_print_t *print, mp_obj_t o_in, mp_pr
             if (o->base.type == &mp_type_OSError && MP_OBJ_IS_SMALL_INT(o->args->items[0])) {
                 qstr qst = mp_errno_to_str(o->args->items[0]);
                 if (qst != MP_QSTR_NULL) {
-                    mp_printf(print, "[Errno %d] %q", MP_OBJ_SMALL_INT_VALUE(o->args->items[0]), qst);
+                    mp_printf(print, "[Errno " INT_FMT "] %q", MP_OBJ_SMALL_INT_VALUE(o->args->items[0]), qst);
                     return;
                 }
             }
@@ -187,7 +184,7 @@ mp_obj_t mp_obj_exception_get_value(mp_obj_t self_in) {
     }
 }
 
-STATIC void exception_attr(mp_obj_t self_in, qstr attr, mp_obj_t *dest) {
+void mp_obj_exception_attr(mp_obj_t self_in, qstr attr, mp_obj_t *dest) {
     mp_obj_exception_t *self = MP_OBJ_TO_PTR(self_in);
     if (dest[0] != MP_OBJ_NULL) {
         // store/delete attribute
@@ -210,37 +207,12 @@ STATIC void exception_attr(mp_obj_t self_in, qstr attr, mp_obj_t *dest) {
     }
 }
 
-STATIC mp_obj_t exc___init__(size_t n_args, const mp_obj_t *args) {
-    mp_obj_exception_t *self = MP_OBJ_TO_PTR(args[0]);
-    mp_obj_t argst = mp_obj_new_tuple(n_args - 1, args + 1);
-    self->args = MP_OBJ_TO_PTR(argst);
-    return mp_const_none;
-}
-STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(exc___init___obj, 1, MP_OBJ_FUN_ARGS_MAX, exc___init__);
-
-STATIC const mp_rom_map_elem_t exc_locals_dict_table[] = {
-    { MP_ROM_QSTR(MP_QSTR___init__), MP_ROM_PTR(&exc___init___obj) },
-};
-
-STATIC MP_DEFINE_CONST_DICT(exc_locals_dict, exc_locals_dict_table);
-
 const mp_obj_type_t mp_type_BaseException = {
     { &mp_type_type },
     .name = MP_QSTR_BaseException,
     .print = mp_obj_exception_print,
     .make_new = mp_obj_exception_make_new,
-    .attr = exception_attr,
-    .locals_dict = (mp_obj_dict_t*)&exc_locals_dict,
-};
-
-#define MP_DEFINE_EXCEPTION(exc_name, base_name) \
-const mp_obj_type_t mp_type_ ## exc_name = { \
-    { &mp_type_type }, \
-    .name = MP_QSTR_ ## exc_name, \
-    .print = mp_obj_exception_print, \
-    .make_new = mp_obj_exception_make_new, \
-    .attr = exception_attr, \
-    .parent = &mp_type_ ## base_name, \
+    .attr = mp_obj_exception_attr,
 };
 
 // List of all exceptions, arranged as in the table at:
diff --git a/py/objexcept.h b/py/objexcept.h
index f67651a7e..7c3076224 100644
--- a/py/objexcept.h
+++ b/py/objexcept.h
@@ -37,4 +37,17 @@ typedef struct _mp_obj_exception_t {
     mp_obj_tuple_t *args;
 } mp_obj_exception_t;
 
+void mp_obj_exception_print(const mp_print_t *print, mp_obj_t o_in, mp_print_kind_t kind);
+void mp_obj_exception_attr(mp_obj_t self_in, qstr attr, mp_obj_t *dest);
+
+#define MP_DEFINE_EXCEPTION(exc_name, base_name) \
+const mp_obj_type_t mp_type_ ## exc_name = { \
+    { &mp_type_type }, \
+    .name = MP_QSTR_ ## exc_name, \
+    .print = mp_obj_exception_print, \
+    .make_new = mp_obj_exception_make_new, \
+    .attr = mp_obj_exception_attr, \
+    .parent = &mp_type_ ## base_name, \
+};
+
 #endif // MICROPY_INCLUDED_PY_OBJEXCEPT_H
diff --git a/py/objfloat.c b/py/objfloat.c
index fde2224ad..16aa9bc20 100644
--- a/py/objfloat.c
+++ b/py/objfloat.c
@@ -91,7 +91,7 @@ typedef uint32_t mp_float_uint_t;
         if (adj_exp <= MP_FLOAT_FRAC_BITS) {
             // number may have a fraction; xor the integer part with the fractional part
             val = (frc >> (MP_FLOAT_FRAC_BITS - adj_exp))
-                ^ (frc & ((1 << (MP_FLOAT_FRAC_BITS - adj_exp)) - 1));
+                ^ (frc & (((mp_float_uint_t)1 << (MP_FLOAT_FRAC_BITS - adj_exp)) - 1));
         } else if ((unsigned int)adj_exp < BITS_PER_BYTE * sizeof(mp_int_t) - 1) {
             // the number is a (big) whole integer and will fit in val's signed-width
             val = (mp_int_t)frc << (adj_exp - MP_FLOAT_FRAC_BITS);
@@ -102,7 +102,7 @@ typedef uint32_t mp_float_uint_t;
     }
 
     if (u.p.sgn) {
-        val = -val;
+        val = -(mp_uint_t)val;
     }
 
     return val;
@@ -140,12 +140,11 @@ STATIC mp_obj_t float_make_new(const mp_obj_type_t *type_in, size_t n_args, size
             return mp_obj_new_float(0);
 
         case 1:
-        default:
-            if (MP_OBJ_IS_STR(args[0])) {
-                // a string, parse it
-                size_t l;
-                const char *s = mp_obj_str_get_data(args[0], &l);
-                return mp_parse_num_decimal(s, l, false, false, NULL);
+        default: {
+            mp_buffer_info_t bufinfo;
+            if (mp_get_buffer(args[0], &bufinfo, MP_BUFFER_READ)) {
+                // a textual representation, parse it
+                return mp_parse_num_decimal(bufinfo.buf, bufinfo.len, false, false, NULL);
             } else if (mp_obj_is_float(args[0])) {
                 // a float, just return it
                 return args[0];
@@ -153,6 +152,7 @@ STATIC mp_obj_t float_make_new(const mp_obj_type_t *type_in, size_t n_args, size
                 // something else, try to cast it to a float
                 return mp_obj_new_float(mp_obj_get_float(args[0]));
             }
+        }
     }
 }
 
@@ -296,7 +296,7 @@ mp_obj_t mp_obj_float_binary_op(mp_binary_op_t op, mp_float_t lhs_val, mp_obj_t
             break;
         case MP_BINARY_OP_POWER:
         case MP_BINARY_OP_INPLACE_POWER:
-            if (lhs_val == 0 && rhs_val < 0) {
+            if (lhs_val == 0 && rhs_val < 0 && !isinf(rhs_val)) {
                 goto zero_division_error;
             }
             if (lhs_val < 0 && rhs_val != MICROPY_FLOAT_C_FUN(floor)(rhs_val)) {
diff --git a/py/objfun.c b/py/objfun.c
index 030b3f7cb..8c51d92e0 100644
--- a/py/objfun.c
+++ b/py/objfun.c
@@ -195,32 +195,54 @@ STATIC void dump_args(const mp_obj_t *a, size_t sz) {
 // than this will try to use the heap, with fallback to stack allocation.
 #define VM_MAX_STATE_ON_STACK (11 * sizeof(mp_uint_t))
 
-// Set this to enable a simple stack overflow check.
+// Set this to 1 to enable a simple stack overflow check.
 #define VM_DETECT_STACK_OVERFLOW (0)
 
+#define DECODE_CODESTATE_SIZE(bytecode, n_state_out_var, state_size_out_var) \
+    { \
+        /* bytecode prelude: state size and exception stack size */               \
+        n_state_out_var = mp_decode_uint_value(bytecode);                         \
+        size_t n_exc_stack = mp_decode_uint_value(mp_decode_uint_skip(bytecode)); \
+                                                                                  \
+        n_state_out_var += VM_DETECT_STACK_OVERFLOW;                              \
+                                                                                  \
+        /* state size in bytes */                                                 \
+        state_size_out_var = n_state_out_var * sizeof(mp_obj_t)                   \
+                           + n_exc_stack * sizeof(mp_exc_stack_t);                \
+    }
+
+#define INIT_CODESTATE(code_state, _fun_bc, n_args, n_kw, args) \
+    code_state->fun_bc = _fun_bc; \
+    code_state->ip = 0; \
+    mp_setup_code_state(code_state, n_args, n_kw, args); \
+    code_state->old_globals = mp_globals_get();
+
 #if MICROPY_STACKLESS
 mp_code_state_t *mp_obj_fun_bc_prepare_codestate(mp_obj_t self_in, size_t n_args, size_t n_kw, const mp_obj_t *args) {
     MP_STACK_CHECK();
     mp_obj_fun_bc_t *self = MP_OBJ_TO_PTR(self_in);
 
-    // bytecode prelude: state size and exception stack size
-    size_t n_state = mp_decode_uint_value(self->bytecode);
-    size_t n_exc_stack = mp_decode_uint_value(mp_decode_uint_skip(self->bytecode));
+    size_t n_state, state_size;
+    DECODE_CODESTATE_SIZE(self->bytecode, n_state, state_size);
 
-    // allocate state for locals and stack
-    size_t state_size = n_state * sizeof(mp_obj_t) + n_exc_stack * sizeof(mp_exc_stack_t);
     mp_code_state_t *code_state;
+    #if MICROPY_ENABLE_PYSTACK
+    code_state = mp_pystack_alloc(sizeof(mp_code_state_t) + state_size);
+    #else
+    // If we use m_new_obj_var(), then on no memory, MemoryError will be
+    // raised. But this is not correct exception for a function call,
+    // RuntimeError should be raised instead. So, we use m_new_obj_var_maybe(),
+    // return NULL, then vm.c takes the needed action (either raise
+    // RuntimeError or fallback to stack allocation).
     code_state = m_new_obj_var_maybe(mp_code_state_t, byte, state_size);
     if (!code_state) {
         return NULL;
     }
+    #endif
 
-    code_state->fun_bc = self;
-    code_state->ip = 0;
-    mp_setup_code_state(code_state, n_args, n_kw, args);
+    INIT_CODESTATE(code_state, self, n_args, n_kw, args);
 
     // execute the byte code with the correct globals context
-    code_state->old_globals = mp_globals_get();
     mp_globals_set(self->globals);
 
     return code_state;
@@ -238,17 +260,14 @@ STATIC mp_obj_t fun_bc_call(mp_obj_t self_in, size_t n_args, size_t n_kw, const
     mp_obj_fun_bc_t *self = MP_OBJ_TO_PTR(self_in);
     DEBUG_printf("Func n_def_args: %d\n", self->n_def_args);
 
-    // bytecode prelude: state size and exception stack size
-    size_t n_state = mp_decode_uint_value(self->bytecode);
-    size_t n_exc_stack = mp_decode_uint_value(mp_decode_uint_skip(self->bytecode));
-
-#if VM_DETECT_STACK_OVERFLOW
-    n_state += 1;
-#endif
+    size_t n_state, state_size;
+    DECODE_CODESTATE_SIZE(self->bytecode, n_state, state_size);
 
     // allocate state for locals and stack
-    size_t state_size = n_state * sizeof(mp_obj_t) + n_exc_stack * sizeof(mp_exc_stack_t);
     mp_code_state_t *code_state = NULL;
+    #if MICROPY_ENABLE_PYSTACK
+    code_state = mp_pystack_alloc(sizeof(mp_code_state_t) + state_size);
+    #else
     if (state_size > VM_MAX_STATE_ON_STACK) {
         code_state = m_new_obj_var_maybe(mp_code_state_t, byte, state_size);
     }
@@ -256,13 +275,11 @@ STATIC mp_obj_t fun_bc_call(mp_obj_t self_in, size_t n_args, size_t n_kw, const
         code_state = alloca(sizeof(mp_code_state_t) + state_size);
         state_size = 0; // indicate that we allocated using alloca
     }
+    #endif
 
-    code_state->fun_bc = self;
-    code_state->ip = 0;
-    mp_setup_code_state(code_state, n_args, n_kw, args);
+    INIT_CODESTATE(code_state, self, n_args, n_kw, args);
 
     // execute the byte code with the correct globals context
-    code_state->old_globals = mp_globals_get();
     mp_globals_set(self->globals);
     mp_vm_return_kind_t vm_return_kind = mp_execute_bytecode(code_state, MP_OBJ_NULL);
     mp_globals_set(code_state->old_globals);
@@ -304,10 +321,14 @@ STATIC mp_obj_t fun_bc_call(mp_obj_t self_in, size_t n_args, size_t n_kw, const
         result = code_state->state[n_state - 1];
     }
 
+    #if MICROPY_ENABLE_PYSTACK
+    mp_pystack_free(code_state);
+    #else
     // free the state if it was allocated on the heap
     if (state_size != 0) {
         m_del_var(mp_code_state_t, byte, state_size, code_state);
     }
+    #endif
 
     if (vm_return_kind == MP_VM_RETURN_NORMAL) {
         return result;
diff --git a/py/objgenerator.c b/py/objgenerator.c
index ff566c076..5664052f5 100644
--- a/py/objgenerator.c
+++ b/py/objgenerator.c
@@ -4,7 +4,7 @@
  * The MIT License (MIT)
  *
  * Copyright (c) 2013, 2014 Damien P. George
- * Copyright (c) 2014 Paul Sokolovsky
+ * Copyright (c) 2014-2017 Paul Sokolovsky
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -106,12 +106,31 @@ mp_vm_return_kind_t mp_obj_gen_resume(mp_obj_t self_in, mp_obj_t send_value, mp_
             mp_raise_TypeError("can't send non-None value to a just-started generator");
         }
     } else {
-        *self->code_state.sp = send_value;
+        #if MICROPY_PY_GENERATOR_PEND_THROW
+        // If exception is pending (set using .pend_throw()), process it now.
+        if (*self->code_state.sp != mp_const_none) {
+            throw_value = *self->code_state.sp;
+            *self->code_state.sp = MP_OBJ_NULL;
+        } else
+        #endif
+        {
+            *self->code_state.sp = send_value;
+        }
+    }
+
+    // We set self->globals=NULL while executing, for a sentinel to ensure the generator
+    // cannot be reentered during execution
+    if (self->globals == NULL) {
+        mp_raise_ValueError("generator already executing");
     }
-    mp_obj_dict_t *old_globals = mp_globals_get();
+
+    // Set up the correct globals context for the generator and execute it
+    self->code_state.old_globals = mp_globals_get();
     mp_globals_set(self->globals);
+    self->globals = NULL;
     mp_vm_return_kind_t ret_kind = mp_execute_bytecode(&self->code_state, throw_value);
-    mp_globals_set(old_globals);
+    self->globals = mp_globals_get();
+    mp_globals_set(self->code_state.old_globals);
 
     switch (ret_kind) {
         case MP_VM_RETURN_NORMAL:
@@ -127,9 +146,9 @@ mp_vm_return_kind_t mp_obj_gen_resume(mp_obj_t self_in, mp_obj_t send_value, mp_
 
         case MP_VM_RETURN_YIELD:
             *ret_val = *self->code_state.sp;
-            if (*ret_val == MP_OBJ_STOP_ITERATION) {
-                self->code_state.ip = 0;
-            }
+            #if MICROPY_PY_GENERATOR_PEND_THROW
+            *self->code_state.sp = mp_const_none;
+            #endif
             break;
 
         case MP_VM_RETURN_EXCEPTION: {
@@ -224,10 +243,24 @@ STATIC mp_obj_t gen_instance_close(mp_obj_t self_in) {
 
 STATIC MP_DEFINE_CONST_FUN_OBJ_1(gen_instance_close_obj, gen_instance_close);
 
+STATIC mp_obj_t gen_instance_pend_throw(mp_obj_t self_in, mp_obj_t exc_in) {
+    mp_obj_gen_instance_t *self = MP_OBJ_TO_PTR(self_in);
+    if (self->code_state.sp == self->code_state.state - 1) {
+        mp_raise_TypeError("can't pend throw to just-started generator");
+    }
+    mp_obj_t prev = *self->code_state.sp;
+    *self->code_state.sp = exc_in;
+    return prev;
+}
+STATIC MP_DEFINE_CONST_FUN_OBJ_2(gen_instance_pend_throw_obj, gen_instance_pend_throw);
+
 STATIC const mp_rom_map_elem_t gen_instance_locals_dict_table[] = {
     { MP_ROM_QSTR(MP_QSTR_close), MP_ROM_PTR(&gen_instance_close_obj) },
     { MP_ROM_QSTR(MP_QSTR_send), MP_ROM_PTR(&gen_instance_send_obj) },
     { MP_ROM_QSTR(MP_QSTR_throw), MP_ROM_PTR(&gen_instance_throw_obj) },
+    #if MICROPY_PY_GENERATOR_PEND_THROW
+    { MP_ROM_QSTR(MP_QSTR_pend_throw), MP_ROM_PTR(&gen_instance_pend_throw_obj) },
+    #endif
 };
 
 STATIC MP_DEFINE_CONST_DICT(gen_instance_locals_dict, gen_instance_locals_dict_table);
diff --git a/py/objint.c b/py/objint.c
index 4f2e610a5..270e16969 100644
--- a/py/objint.c
+++ b/py/objint.c
@@ -222,27 +222,26 @@ size_t mp_int_format_size(size_t num_bits, int base, const char *prefix, char co
 char *mp_obj_int_formatted(char **buf, size_t *buf_size, size_t *fmt_size, mp_const_obj_t self_in,
                            int base, const char *prefix, char base_char, char comma) {
     fmt_int_t num;
+    #if MICROPY_LONGINT_IMPL == MICROPY_LONGINT_IMPL_NONE
+    // Only have small ints; get the integer value to format.
+    num = MP_OBJ_SMALL_INT_VALUE(self_in);
+    #else
     if (MP_OBJ_IS_SMALL_INT(self_in)) {
         // A small int; get the integer value to format.
         num = MP_OBJ_SMALL_INT_VALUE(self_in);
-#if MICROPY_LONGINT_IMPL != MICROPY_LONGINT_IMPL_NONE
-    } else if (MP_OBJ_IS_TYPE(self_in, &mp_type_int)) {
+    } else {
+        assert(MP_OBJ_IS_TYPE(self_in, &mp_type_int));
         // Not a small int.
-#if MICROPY_LONGINT_IMPL == MICROPY_LONGINT_IMPL_LONGLONG
+        #if MICROPY_LONGINT_IMPL == MICROPY_LONGINT_IMPL_LONGLONG
         const mp_obj_int_t *self = self_in;
         // Get the value to format; mp_obj_get_int truncates to mp_int_t.
         num = self->val;
-#else
+        #else
         // Delegate to the implementation for the long int.
         return mp_obj_int_formatted_impl(buf, buf_size, fmt_size, self_in, base, prefix, base_char, comma);
-#endif
-#endif
-    } else {
-        // Not an int.
-        **buf = '\0';
-        *fmt_size = 0;
-        return *buf;
+        #endif
     }
+    #endif
 
     char sign = '\0';
     if (num < 0) {
@@ -378,7 +377,7 @@ mp_obj_t mp_obj_int_binary_op_extra_cases(mp_binary_op_t op, mp_obj_t lhs_in, mp
         // true acts as 0
         return mp_binary_op(op, lhs_in, MP_OBJ_NEW_SMALL_INT(1));
     } else if (op == MP_BINARY_OP_MULTIPLY) {
-        if (MP_OBJ_IS_STR(rhs_in) || MP_OBJ_IS_TYPE(rhs_in, &mp_type_bytes) || MP_OBJ_IS_TYPE(rhs_in, &mp_type_tuple) || MP_OBJ_IS_TYPE(rhs_in, &mp_type_list)) {
+        if (MP_OBJ_IS_STR_OR_BYTES(rhs_in) || MP_OBJ_IS_TYPE(rhs_in, &mp_type_tuple) || MP_OBJ_IS_TYPE(rhs_in, &mp_type_list)) {
             // multiply is commutative for these types, so delegate to them
             return mp_binary_op(op, rhs_in, lhs_in);
         }
diff --git a/py/objint_longlong.c b/py/objint_longlong.c
index 2e567c572..cb8d1672d 100644
--- a/py/objint_longlong.c
+++ b/py/objint_longlong.c
@@ -124,10 +124,9 @@ mp_obj_t mp_obj_int_binary_op(mp_binary_op_t op, mp_obj_t lhs_in, mp_obj_t rhs_i
 
     if (MP_OBJ_IS_SMALL_INT(lhs_in)) {
         lhs_val = MP_OBJ_SMALL_INT_VALUE(lhs_in);
-    } else if (MP_OBJ_IS_TYPE(lhs_in, &mp_type_int)) {
-        lhs_val = ((mp_obj_int_t*)lhs_in)->val;
     } else {
-        return MP_OBJ_NULL; // op not supported
+        assert(MP_OBJ_IS_TYPE(lhs_in, &mp_type_int));
+        lhs_val = ((mp_obj_int_t*)lhs_in)->val;
     }
 
     if (MP_OBJ_IS_SMALL_INT(rhs_in)) {
@@ -151,9 +150,15 @@ mp_obj_t mp_obj_int_binary_op(mp_binary_op_t op, mp_obj_t lhs_in, mp_obj_t rhs_i
             return mp_obj_new_int_from_ll(lhs_val * rhs_val);
         case MP_BINARY_OP_FLOOR_DIVIDE:
         case MP_BINARY_OP_INPLACE_FLOOR_DIVIDE:
+            if (rhs_val == 0) {
+                goto zero_division;
+            }
             return mp_obj_new_int_from_ll(lhs_val / rhs_val);
         case MP_BINARY_OP_MODULO:
         case MP_BINARY_OP_INPLACE_MODULO:
+            if (rhs_val == 0) {
+                goto zero_division;
+            }
             return mp_obj_new_int_from_ll(lhs_val % rhs_val);
 
         case MP_BINARY_OP_AND:
@@ -210,6 +215,9 @@ mp_obj_t mp_obj_int_binary_op(mp_binary_op_t op, mp_obj_t lhs_in, mp_obj_t rhs_i
         default:
             return MP_OBJ_NULL; // op not supported
     }
+
+zero_division:
+    mp_raise_msg(&mp_type_ZeroDivisionError, "division by zero");
 }
 
 mp_obj_t mp_obj_new_int(mp_int_t value) {
diff --git a/py/objint_mpz.c b/py/objint_mpz.c
index 808fae6e4..6ee128640 100644
--- a/py/objint_mpz.c
+++ b/py/objint_mpz.c
@@ -170,11 +170,9 @@ mp_obj_t mp_obj_int_binary_op(mp_binary_op_t op, mp_obj_t lhs_in, mp_obj_t rhs_i
     if (MP_OBJ_IS_SMALL_INT(lhs_in)) {
         mpz_init_fixed_from_int(&z_int, z_int_dig, MPZ_NUM_DIG_FOR_INT, MP_OBJ_SMALL_INT_VALUE(lhs_in));
         zlhs = &z_int;
-    } else if (MP_OBJ_IS_TYPE(lhs_in, &mp_type_int)) {
-        zlhs = &((mp_obj_int_t*)MP_OBJ_TO_PTR(lhs_in))->mpz;
     } else {
-        // unsupported type
-        return MP_OBJ_NULL;
+        assert(MP_OBJ_IS_TYPE(lhs_in, &mp_type_int));
+        zlhs = &((mp_obj_int_t*)MP_OBJ_TO_PTR(lhs_in))->mpz;
     }
 
     // if rhs is small int, then lhs was not (otherwise mp_binary_op handles it)
@@ -207,7 +205,7 @@ mp_obj_t mp_obj_int_binary_op(mp_binary_op_t op, mp_obj_t lhs_in, mp_obj_t rhs_i
         return mp_obj_new_float(flhs / frhs);
 #endif
 
-    } else if (op >= MP_BINARY_OP_INPLACE_OR) {
+    } else if (op >= MP_BINARY_OP_INPLACE_OR && op < MP_BINARY_OP_CONTAINS) {
         mp_obj_int_t *res = mp_obj_int_new_mpz();
 
         switch (op) {
diff --git a/py/objlist.h b/py/objlist.h
index 28b5495a9..a43663db7 100644
--- a/py/objlist.h
+++ b/py/objlist.h
@@ -35,4 +35,6 @@ typedef struct _mp_obj_list_t {
     mp_obj_t *items;
 } mp_obj_list_t;
 
+void mp_obj_list_init(mp_obj_list_t *o, size_t n);
+
 #endif // MICROPY_INCLUDED_PY_OBJLIST_H
diff --git a/py/objmodule.c b/py/objmodule.c
index e3464ecfa..b28fb2416 100644
--- a/py/objmodule.c
+++ b/py/objmodule.c
@@ -259,17 +259,7 @@ mp_obj_t mp_module_get(qstr module_name) {
         if (el == NULL) {
             return MP_OBJ_NULL;
         }
-
-        if (MICROPY_MODULE_BUILTIN_INIT) {
-            // look for __init__ and call it if it exists
-            mp_obj_t dest[2];
-            mp_load_method_maybe(el->value, MP_QSTR___init__, dest);
-            if (dest[0] != MP_OBJ_NULL) {
-                mp_call_method_n_kw(0, 0, dest);
-                // register module so __init__ is not called again
-                mp_module_register(module_name, el->value);
-            }
-        }
+        mp_module_call_init(module_name, el->value);
     }
 
     // module found, return it
@@ -280,3 +270,19 @@ void mp_module_register(qstr qst, mp_obj_t module) {
     mp_map_t *mp_loaded_modules_map = &MP_STATE_VM(mp_loaded_modules_dict).map;
     mp_map_lookup(mp_loaded_modules_map, MP_OBJ_NEW_QSTR(qst), MP_MAP_LOOKUP_ADD_IF_NOT_FOUND)->value = module;
 }
+
+#if MICROPY_MODULE_BUILTIN_INIT
+void mp_module_call_init(qstr module_name, mp_obj_t module_obj) {
+    // Look for __init__ and call it if it exists
+    mp_obj_t dest[2];
+    mp_load_method_maybe(module_obj, MP_QSTR___init__, dest);
+    if (dest[0] != MP_OBJ_NULL) {
+        mp_call_method_n_kw(0, 0, dest);
+        // Register module so __init__ is not called again.
+        // If a module can be referenced by more than one name (eg due to weak links)
+        // then __init__ will still be called for each distinct import, and it's then
+        // up to the particular module to make sure it's __init__ code only runs once.
+        mp_module_register(module_name, module_obj);
+    }
+}
+#endif
diff --git a/py/objmodule.h b/py/objmodule.h
index b5c07dc33..b7702ec50 100644
--- a/py/objmodule.h
+++ b/py/objmodule.h
@@ -34,4 +34,13 @@ extern const mp_map_t mp_builtin_module_weak_links_map;
 mp_obj_t mp_module_get(qstr module_name);
 void mp_module_register(qstr qstr, mp_obj_t module);
 
+#if MICROPY_MODULE_BUILTIN_INIT
+void mp_module_call_init(qstr module_name, mp_obj_t module_obj);
+#else
+static inline void mp_module_call_init(qstr module_name, mp_obj_t module_obj) {
+    (void)module_name;
+    (void)module_obj;
+}
+#endif
+
 #endif // MICROPY_INCLUDED_PY_OBJMODULE_H
diff --git a/py/objnamedtuple.c b/py/objnamedtuple.c
index 2288fa7b6..832a4a671 100644
--- a/py/objnamedtuple.c
+++ b/py/objnamedtuple.c
@@ -27,15 +27,14 @@
 
 #include <string.h>
 
-#include "py/nlr.h"
-#include "py/objnamedtuple.h"
 #include "py/objtuple.h"
 #include "py/runtime.h"
 #include "py/objstr.h"
+#include "py/objnamedtuple.h"
 
 #if MICROPY_PY_COLLECTIONS
 
-STATIC size_t namedtuple_find_field(const mp_obj_namedtuple_type_t *type, qstr name) {
+size_t mp_obj_namedtuple_find_field(const mp_obj_namedtuple_type_t *type, qstr name) {
     for (size_t i = 0; i < type->n_fields; i++) {
         if (type->fields[i] == name) {
             return i;
@@ -44,7 +43,24 @@ STATIC size_t namedtuple_find_field(const mp_obj_namedtuple_type_t *type, qstr n
     return (size_t)-1;
 }
 
-void namedtuple_print(const mp_print_t *print, mp_obj_t o_in, mp_print_kind_t kind) {
+#if MICROPY_PY_COLLECTIONS_NAMEDTUPLE__ASDICT
+STATIC mp_obj_t namedtuple_asdict(mp_obj_t self_in) {
+    mp_obj_namedtuple_t *self = MP_OBJ_TO_PTR(self_in);
+    const qstr *fields = ((mp_obj_namedtuple_type_t*)self->tuple.base.type)->fields;
+    mp_obj_t dict = mp_obj_new_dict(self->tuple.len);
+    //make it an OrderedDict
+    mp_obj_dict_t *dictObj = MP_OBJ_TO_PTR(dict);
+    dictObj->base.type = &mp_type_ordereddict;
+    dictObj->map.is_ordered = 1;
+    for (size_t i = 0; i < self->tuple.len; ++i) {
+        mp_obj_dict_store(dict, MP_OBJ_NEW_QSTR(fields[i]), self->tuple.items[i]);
+    }
+    return dict;
+}
+MP_DEFINE_CONST_FUN_OBJ_1(namedtuple_asdict_obj, namedtuple_asdict);
+#endif
+
+STATIC void namedtuple_print(const mp_print_t *print, mp_obj_t o_in, mp_print_kind_t kind) {
     (void)kind;
     mp_obj_namedtuple_t *o = MP_OBJ_TO_PTR(o_in);
     mp_printf(print, "%q", o->tuple.base.type->name);
@@ -52,11 +68,18 @@ void namedtuple_print(const mp_print_t *print, mp_obj_t o_in, mp_print_kind_t ki
     mp_obj_attrtuple_print_helper(print, fields, &o->tuple);
 }
 
-void namedtuple_attr(mp_obj_t self_in, qstr attr, mp_obj_t *dest) {
+STATIC void namedtuple_attr(mp_obj_t self_in, qstr attr, mp_obj_t *dest) {
     if (dest[0] == MP_OBJ_NULL) {
         // load attribute
         mp_obj_namedtuple_t *self = MP_OBJ_TO_PTR(self_in);
-        size_t id = namedtuple_find_field((mp_obj_namedtuple_type_t*)self->tuple.base.type, attr);
+        #if MICROPY_PY_COLLECTIONS_NAMEDTUPLE__ASDICT
+        if (attr == MP_QSTR__asdict) {
+            dest[0] = MP_OBJ_FROM_PTR(&namedtuple_asdict_obj);
+            dest[1] = self_in;
+            return;
+        }
+        #endif
+        size_t id = mp_obj_namedtuple_find_field((mp_obj_namedtuple_type_t*)self->tuple.base.type, attr);
         if (id == (size_t)-1) {
             return;
         }
@@ -96,7 +119,7 @@ mp_obj_t namedtuple_make_new(const mp_obj_type_t *type_in, size_t n_args, size_t
     memset(&tuple->items[n_args], 0, sizeof(mp_obj_t) * n_kw);
     for (size_t i = n_args; i < n_args + 2 * n_kw; i += 2) {
         qstr kw = mp_obj_str_get_qstr(args[i]);
-        size_t id = namedtuple_find_field(type, kw);
+        size_t id = mp_obj_namedtuple_find_field(type, kw);
         if (id == (size_t)-1) {
             if (MICROPY_ERROR_REPORTING == MICROPY_ERROR_REPORTING_TERSE) {
                 mp_arg_error_terse_mismatch();
@@ -119,9 +142,18 @@ mp_obj_t namedtuple_make_new(const mp_obj_type_t *type_in, size_t n_args, size_t
     return MP_OBJ_FROM_PTR(tuple);
 }
 
-STATIC mp_obj_t mp_obj_new_namedtuple_type(qstr name, size_t n_fields, mp_obj_t *fields) {
+mp_obj_namedtuple_type_t *mp_obj_new_namedtuple_base(size_t n_fields, mp_obj_t *fields) {
     mp_obj_namedtuple_type_t *o = m_new_obj_var(mp_obj_namedtuple_type_t, qstr, n_fields);
     memset(&o->base, 0, sizeof(o->base));
+    o->n_fields = n_fields;
+    for (size_t i = 0; i < n_fields; i++) {
+        o->fields[i] = mp_obj_str_get_qstr(fields[i]);
+    }
+    return o;
+}
+
+STATIC mp_obj_t mp_obj_new_namedtuple_type(qstr name, size_t n_fields, mp_obj_t *fields) {
+    mp_obj_namedtuple_type_t *o = mp_obj_new_namedtuple_base(n_fields, fields);
     o->base.base.type = &mp_type_type;
     o->base.name = name;
     o->base.print = namedtuple_print;
@@ -132,10 +164,6 @@ STATIC mp_obj_t mp_obj_new_namedtuple_type(qstr name, size_t n_fields, mp_obj_t
     o->base.subscr = mp_obj_tuple_subscr;
     o->base.getiter = mp_obj_tuple_getiter;
     o->base.parent = &mp_type_tuple;
-    o->n_fields = n_fields;
-    for (size_t i = 0; i < n_fields; i++) {
-        o->fields[i] = mp_obj_str_get_qstr(fields[i]);
-    }
     return MP_OBJ_FROM_PTR(o);
 }
 
diff --git a/py/objnamedtuple.h b/py/objnamedtuple.h
index a36404b8d..d32af35af 100644
--- a/py/objnamedtuple.h
+++ b/py/objnamedtuple.h
@@ -1,10 +1,9 @@
 /*
- * This file is part of the Micro Python project, http://micropython.org/
+ * This file is part of the MicroPython project, http://micropython.org/
  *
  * The MIT License (MIT)
  *
- * Copyright (c) 2013, 2014 Damien P. George
- * Copyright (c) 2014 Paul Sokolovsky
+ * Copyright (c) 2014-2017 Paul Sokolovsky
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -24,22 +23,14 @@
  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  * THE SOFTWARE.
  */
-
 #ifndef MICROPY_INCLUDED_PY_OBJNAMEDTUPLE_H
 #define MICROPY_INCLUDED_PY_OBJNAMEDTUPLE_H
 
-#include <string.h>
-
-#include "py/nlr.h"
 #include "py/objtuple.h"
-#include "py/runtime.h"
-#include "py/objstr.h"
-
-#if MICROPY_PY_COLLECTIONS
 
 typedef struct _mp_obj_namedtuple_type_t {
     mp_obj_type_t base;
-    mp_uint_t n_fields;
+    size_t n_fields;
     qstr fields[];
 } mp_obj_namedtuple_type_t;
 
@@ -47,12 +38,7 @@ typedef struct _mp_obj_namedtuple_t {
     mp_obj_tuple_t tuple;
 } mp_obj_namedtuple_t;
 
-void namedtuple_print(const mp_print_t *print, mp_obj_t o_in, mp_print_kind_t kind);
-
-void namedtuple_attr(mp_obj_t self_in, qstr attr, mp_obj_t *dest);
-
-mp_obj_t namedtuple_make_new(const mp_obj_type_t *type_in, size_t n_args, size_t n_kw, const mp_obj_t *args);
-
-#endif // MICROPY_PY_COLLECTIONS
+size_t mp_obj_namedtuple_find_field(const mp_obj_namedtuple_type_t *type, qstr name);
+mp_obj_namedtuple_type_t *mp_obj_new_namedtuple_base(size_t n_fields, mp_obj_t *fields);
 
-#endif  // MICROPY_INCLUDED_PY_OBJNAMEDTUPLE_H
+#endif // MICROPY_INCLUDED_PY_OBJNAMEDTUPLE_H
diff --git a/py/objobject.c b/py/objobject.c
index 49d2ec62e..265fcfbf2 100644
--- a/py/objobject.c
+++ b/py/objobject.c
@@ -52,9 +52,12 @@ STATIC mp_obj_t object___new__(mp_obj_t cls) {
     if (!MP_OBJ_IS_TYPE(cls, &mp_type_type) || !mp_obj_is_instance_type((mp_obj_type_t*)MP_OBJ_TO_PTR(cls))) {
         mp_raise_TypeError("__new__ arg must be a user-type");
     }
-    mp_obj_t o = MP_OBJ_SENTINEL;
-    mp_obj_t res = mp_obj_instance_make_new(MP_OBJ_TO_PTR(cls), 1, 0, &o);
-    return res;
+    // This executes only "__new__" part of instance creation.
+    // TODO: This won't work well for classes with native bases.
+    // TODO: This is a hack, should be resolved along the lines of
+    // https://github.com/micropython/micropython/issues/606#issuecomment-43685883
+    const mp_obj_type_t *native_base;
+    return MP_OBJ_FROM_PTR(mp_obj_new_instance(MP_OBJ_TO_PTR(cls), &native_base));
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_1(object___new___fun_obj, object___new__);
 STATIC MP_DEFINE_CONST_STATICMETHOD_OBJ(object___new___obj, MP_ROM_PTR(&object___new___fun_obj));
diff --git a/py/objrange.c b/py/objrange.c
index 3874adb11..86aa0ccfe 100644
--- a/py/objrange.c
+++ b/py/objrange.c
@@ -138,6 +138,24 @@ STATIC mp_obj_t range_unary_op(mp_unary_op_t op, mp_obj_t self_in) {
     }
 }
 
+#if MICROPY_PY_BUILTINS_RANGE_BINOP
+STATIC mp_obj_t range_binary_op(mp_binary_op_t op, mp_obj_t lhs_in, mp_obj_t rhs_in) {
+    if (!MP_OBJ_IS_TYPE(rhs_in, &mp_type_range) || op != MP_BINARY_OP_EQUAL) {
+        return MP_OBJ_NULL; // op not supported
+    }
+    mp_obj_range_t *lhs = MP_OBJ_TO_PTR(lhs_in);
+    mp_obj_range_t *rhs = MP_OBJ_TO_PTR(rhs_in);
+    mp_int_t lhs_len = range_len(lhs);
+    mp_int_t rhs_len = range_len(rhs);
+    return mp_obj_new_bool(
+        lhs_len == rhs_len
+        && (lhs_len == 0
+            || (lhs->start == rhs->start
+                && (lhs_len == 1 || lhs->step == rhs->step)))
+    );
+}
+#endif
+
 STATIC mp_obj_t range_subscr(mp_obj_t self_in, mp_obj_t index, mp_obj_t value) {
     if (value == MP_OBJ_SENTINEL) {
         // load
@@ -195,6 +213,9 @@ const mp_obj_type_t mp_type_range = {
     .print = range_print,
     .make_new = range_make_new,
     .unary_op = range_unary_op,
+    #if MICROPY_PY_BUILTINS_RANGE_BINOP
+    .binary_op = range_binary_op,
+    #endif
     .subscr = range_subscr,
     .getiter = range_getiter,
 #if MICROPY_PY_BUILTINS_RANGE_ATTRS
diff --git a/py/objset.c b/py/objset.c
index 6ed15c791..799ba9df0 100644
--- a/py/objset.c
+++ b/py/objset.c
@@ -351,11 +351,9 @@ STATIC mp_obj_t set_issuperset_proper(mp_obj_t self_in, mp_obj_t other_in) {
 }
 
 STATIC mp_obj_t set_equal(mp_obj_t self_in, mp_obj_t other_in) {
+    assert(is_set_or_frozenset(other_in));
     check_set_or_frozenset(self_in);
     mp_obj_set_t *self = MP_OBJ_TO_PTR(self_in);
-    if (!is_set_or_frozenset(other_in)) {
-        return mp_const_false;
-    }
     mp_obj_set_t *other = MP_OBJ_TO_PTR(other_in);
     if (self->set.used != other->set.used) {
         return mp_const_false;
@@ -461,7 +459,7 @@ STATIC mp_obj_t set_binary_op(mp_binary_op_t op, mp_obj_t lhs, mp_obj_t rhs) {
     #else
     bool update = true;
     #endif
-    if (op != MP_BINARY_OP_IN && !is_set_or_frozenset(rhs)) {
+    if (op != MP_BINARY_OP_CONTAINS && !is_set_or_frozenset(rhs)) {
         // For all ops except containment the RHS must be a set/frozenset
         return MP_OBJ_NULL;
     }
@@ -507,7 +505,7 @@ STATIC mp_obj_t set_binary_op(mp_binary_op_t op, mp_obj_t lhs, mp_obj_t rhs) {
             return set_issubset(lhs, rhs);
         case MP_BINARY_OP_MORE_EQUAL:
             return set_issuperset(lhs, rhs);
-        case MP_BINARY_OP_IN: {
+        case MP_BINARY_OP_CONTAINS: {
             mp_obj_set_t *o = MP_OBJ_TO_PTR(lhs);
             mp_obj_t elem = mp_set_lookup(&o->set, rhs, MP_MAP_LOOKUP);
             return mp_obj_new_bool(elem != MP_OBJ_NULL);
diff --git a/py/objstr.c b/py/objstr.c
index 7ace1cf73..aae5301ec 100644
--- a/py/objstr.c
+++ b/py/objstr.c
@@ -164,7 +164,14 @@ mp_obj_t mp_obj_str_make_new(const mp_obj_type_t *type, size_t n_args, size_t n_
                     mp_raise_msg(&mp_type_UnicodeError, NULL);
                 }
                 #endif
-                mp_obj_str_t *o = MP_OBJ_TO_PTR(mp_obj_new_str_of_type(type, NULL, str_len));
+
+                // Check if a qstr with this data already exists
+                qstr q = qstr_find_strn((const char*)str_data, str_len);
+                if (q != MP_QSTR_NULL) {
+                    return MP_OBJ_NEW_QSTR(q);
+                }
+
+                mp_obj_str_t *o = MP_OBJ_TO_PTR(mp_obj_new_str_copy(type, NULL, str_len));
                 o->data = str_data;
                 o->hash = str_hash;
                 return MP_OBJ_FROM_PTR(o);
@@ -176,7 +183,7 @@ mp_obj_t mp_obj_str_make_new(const mp_obj_type_t *type, size_t n_args, size_t n_
                     mp_raise_msg(&mp_type_UnicodeError, NULL);
                 }
                 #endif
-                return mp_obj_new_str(bufinfo.buf, bufinfo.len, false);
+                return mp_obj_new_str(bufinfo.buf, bufinfo.len);
             }
     }
 }
@@ -205,7 +212,7 @@ STATIC mp_obj_t bytes_make_new(const mp_obj_type_t *type_in, size_t n_args, size
         if (str_hash == 0) {
             str_hash = qstr_compute_hash(str_data, str_len);
         }
-        mp_obj_str_t *o = MP_OBJ_TO_PTR(mp_obj_new_str_of_type(&mp_type_bytes, NULL, str_len));
+        mp_obj_str_t *o = MP_OBJ_TO_PTR(mp_obj_new_str_copy(&mp_type_bytes, NULL, str_len));
         o->data = str_data;
         o->hash = str_hash;
         return MP_OBJ_FROM_PTR(o);
@@ -216,7 +223,10 @@ STATIC mp_obj_t bytes_make_new(const mp_obj_type_t *type_in, size_t n_args, size
     }
 
     if (MP_OBJ_IS_SMALL_INT(args[0])) {
-        uint len = MP_OBJ_SMALL_INT_VALUE(args[0]);
+        mp_int_t len = MP_OBJ_SMALL_INT_VALUE(args[0]);
+        if (len < 0) {
+            mp_raise_ValueError(NULL);
+        }
         vstr_t vstr;
         vstr_init_len(&vstr, len);
         memset(vstr.buf, 0, len);
@@ -226,7 +236,7 @@ STATIC mp_obj_t bytes_make_new(const mp_obj_type_t *type_in, size_t n_args, size
     // check if argument has the buffer protocol
     mp_buffer_info_t bufinfo;
     if (mp_get_buffer(args[0], &bufinfo, MP_BUFFER_READ)) {
-        return mp_obj_new_str_of_type(&mp_type_bytes, bufinfo.buf, bufinfo.len);
+        return mp_obj_new_bytes(bufinfo.buf, bufinfo.len);
     }
 
     vstr_t vstr;
@@ -377,8 +387,7 @@ mp_obj_t mp_obj_str_binary_op(mp_binary_op_t op, mp_obj_t lhs_in, mp_obj_t rhs_i
             return mp_obj_new_str_from_vstr(lhs_type, &vstr);
         }
 
-        case MP_BINARY_OP_IN:
-            /* NOTE `a in b` is `b.__contains__(a)` */
+        case MP_BINARY_OP_CONTAINS:
             return mp_obj_new_bool(find_subbytes(lhs_data, lhs_len, rhs_data, rhs_len, 1) != NULL);
 
         //case MP_BINARY_OP_NOT_EQUAL: // This is never passed here
@@ -423,7 +432,7 @@ STATIC mp_obj_t bytes_subscr(mp_obj_t self_in, mp_obj_t index, mp_obj_t value) {
         if (MICROPY_PY_BUILTINS_STR_UNICODE || type == &mp_type_bytes) {
             return MP_OBJ_NEW_SMALL_INT(self_data[index_val]);
         } else {
-            return mp_obj_new_str((char*)&self_data[index_val], 1, true);
+            return mp_obj_new_str_via_qstr((char*)&self_data[index_val], 1);
         }
     } else {
         return MP_OBJ_NULL; // op not supported
@@ -654,9 +663,7 @@ STATIC mp_obj_t str_rsplit(size_t n_args, const mp_obj_t *args) {
             }
             res->items[idx--] = mp_obj_new_str_of_type(self_type, s + sep_len, last - s - sep_len);
             last = s;
-            if (splits > 0) {
-                splits--;
-            }
+            splits--;
         }
         if (idx != 0) {
             // We split less parts than split limit, now go cleanup surplus
@@ -1050,7 +1057,7 @@ STATIC vstr_t mp_obj_str_format_helper(const char *str, const char *top, int *ar
             } else {
                 const char *lookup;
                 for (lookup = field_name; lookup < field_name_top && *lookup != '.' && *lookup != '['; lookup++);
-                mp_obj_t field_q = mp_obj_new_str(field_name, lookup - field_name, true/*?*/);
+                mp_obj_t field_q = mp_obj_new_str_via_qstr(field_name, lookup - field_name); // should it be via qstr?
                 field_name = lookup;
                 mp_map_elem_t *key_elem = mp_map_lookup(kwargs, field_q, MP_MAP_LOOKUP);
                 if (key_elem == NULL) {
@@ -1417,7 +1424,7 @@ STATIC mp_obj_t str_modulo_format(mp_obj_t pattern, size_t n_args, const mp_obj_
                 }
                 ++str;
             }
-            mp_obj_t k_obj = mp_obj_new_str((const char*)key, str - key, true);
+            mp_obj_t k_obj = mp_obj_new_str_via_qstr((const char*)key, str - key);
             arg = mp_obj_dict_get(dict, k_obj);
             str++;
         }
@@ -1702,7 +1709,7 @@ STATIC mp_obj_t str_count(size_t n_args, const mp_obj_t *args) {
 
     // if needle_len is zero then we count each gap between characters as an occurrence
     if (needle_len == 0) {
-        return MP_OBJ_NEW_SMALL_INT(unichar_charlen((const char*)start, end - start) + 1);
+        return MP_OBJ_NEW_SMALL_INT(utf8_charlen(start, end - start) + 1);
     }
 
     // count the occurrences
@@ -1981,8 +1988,9 @@ const mp_obj_type_t mp_type_bytes = {
 const mp_obj_str_t mp_const_empty_bytes_obj = {{&mp_type_bytes}, 0, 0, (const byte*)""};
 
 // Create a str/bytes object using the given data.  New memory is allocated and
-// the data is copied across.
-mp_obj_t mp_obj_new_str_of_type(const mp_obj_type_t *type, const byte* data, size_t len) {
+// the data is copied across.  This function should only be used if the type is bytes,
+// or if the type is str and the string data is known to be not interned.
+mp_obj_t mp_obj_new_str_copy(const mp_obj_type_t *type, const byte* data, size_t len) {
     mp_obj_str_t *o = m_new_obj(mp_obj_str_t);
     o->base.type = type;
     o->len = len;
@@ -1996,6 +2004,22 @@ mp_obj_t mp_obj_new_str_of_type(const mp_obj_type_t *type, const byte* data, siz
     return MP_OBJ_FROM_PTR(o);
 }
 
+// Create a str/bytes object using the given data.  If the type is str and the string
+// data is already interned, then a qstr object is returned.  Otherwise new memory is
+// allocated for the object and the data is copied across.
+mp_obj_t mp_obj_new_str_of_type(const mp_obj_type_t *type, const byte* data, size_t len) {
+    if (type == &mp_type_str) {
+        return mp_obj_new_str((const char*)data, len);
+    } else {
+        return mp_obj_new_bytes(data, len);
+    }
+}
+
+// Create a str using a qstr to store the data; may use existing or new qstr.
+mp_obj_t mp_obj_new_str_via_qstr(const char* data, size_t len) {
+    return MP_OBJ_NEW_QSTR(qstr_from_strn(data, len));
+}
+
 // Create a str/bytes object from the given vstr.  The vstr buffer is resized to
 // the exact length required and then reused for the str/bytes object.  The vstr
 // is cleared and can safely be passed to vstr_free if it was heap allocated.
@@ -2026,29 +2050,30 @@ mp_obj_t mp_obj_new_str_from_vstr(const mp_obj_type_t *type, vstr_t *vstr) {
     return MP_OBJ_FROM_PTR(o);
 }
 
-mp_obj_t mp_obj_new_str(const char* data, size_t len, bool make_qstr_if_not_already) {
-    if (make_qstr_if_not_already) {
-        // use existing, or make a new qstr
-        return MP_OBJ_NEW_QSTR(qstr_from_strn(data, len));
+mp_obj_t mp_obj_new_str(const char* data, size_t len) {
+    qstr q = qstr_find_strn(data, len);
+    if (q != MP_QSTR_NULL) {
+        // qstr with this data already exists
+        return MP_OBJ_NEW_QSTR(q);
     } else {
-        qstr q = qstr_find_strn(data, len);
-        if (q != MP_QSTR_NULL) {
-            // qstr with this data already exists
-            return MP_OBJ_NEW_QSTR(q);
-        } else {
-            // no existing qstr, don't make one
-            return mp_obj_new_str_of_type(&mp_type_str, (const byte*)data, len);
-        }
+        // no existing qstr, don't make one
+        return mp_obj_new_str_copy(&mp_type_str, (const byte*)data, len);
     }
 }
 
 mp_obj_t mp_obj_str_intern(mp_obj_t str) {
     GET_STR_DATA_LEN(str, data, len);
-    return MP_OBJ_NEW_QSTR(qstr_from_strn((const char*)data, len));
+    return mp_obj_new_str_via_qstr((const char*)data, len);
+}
+
+mp_obj_t mp_obj_str_intern_checked(mp_obj_t obj) {
+    size_t len;
+    const char *data = mp_obj_str_get_data(obj, &len);
+    return mp_obj_new_str_via_qstr((const char*)data, len);
 }
 
 mp_obj_t mp_obj_new_bytes(const byte* data, size_t len) {
-    return mp_obj_new_str_of_type(&mp_type_bytes, data, len);
+    return mp_obj_new_str_copy(&mp_type_bytes, data, len);
 }
 
 bool mp_obj_str_equal(mp_obj_t s1, mp_obj_t s2) {
@@ -2070,7 +2095,7 @@ bool mp_obj_str_equal(mp_obj_t s1, mp_obj_t s2) {
     }
 }
 
-STATIC void bad_implicit_conversion(mp_obj_t self_in) {
+STATIC NORETURN void bad_implicit_conversion(mp_obj_t self_in) {
     if (MICROPY_ERROR_REPORTING == MICROPY_ERROR_REPORTING_TERSE) {
         mp_raise_TypeError("can't convert to str implicitly");
     } else {
@@ -2142,7 +2167,7 @@ STATIC mp_obj_t str_it_iternext(mp_obj_t self_in) {
     mp_obj_str8_it_t *self = MP_OBJ_TO_PTR(self_in);
     GET_STR_DATA_LEN(self->str, str, len);
     if (self->cur < len) {
-        mp_obj_t o_out = mp_obj_new_str((const char*)str + self->cur, 1, true);
+        mp_obj_t o_out = mp_obj_new_str_via_qstr((const char*)str + self->cur, 1);
         self->cur += 1;
         return o_out;
     } else {
diff --git a/py/objstr.h b/py/objstr.h
index 82501a763..4e55cad09 100644
--- a/py/objstr.h
+++ b/py/objstr.h
@@ -65,6 +65,7 @@ mp_obj_t mp_obj_str_make_new(const mp_obj_type_t *type_in, size_t n_args, size_t
 void mp_str_print_json(const mp_print_t *print, const byte *str_data, size_t str_len);
 mp_obj_t mp_obj_str_format(size_t n_args, const mp_obj_t *args, mp_map_t *kwargs);
 mp_obj_t mp_obj_str_split(size_t n_args, const mp_obj_t *args);
+mp_obj_t mp_obj_new_str_copy(const mp_obj_type_t *type, const byte* data, size_t len);
 mp_obj_t mp_obj_new_str_of_type(const mp_obj_type_t *type, const byte* data, size_t len);
 
 mp_obj_t mp_obj_str_binary_op(mp_binary_op_t op, mp_obj_t lhs_in, mp_obj_t rhs_in);
diff --git a/py/objstringio.c b/py/objstringio.c
index 5c50aa317..b405ee21e 100644
--- a/py/objstringio.c
+++ b/py/objstringio.c
@@ -143,6 +143,17 @@ STATIC mp_uint_t stringio_ioctl(mp_obj_t o_in, mp_uint_t request, uintptr_t arg,
         }
         case MP_STREAM_FLUSH:
             return 0;
+        case MP_STREAM_CLOSE:
+            #if MICROPY_CPYTHON_COMPAT
+            vstr_free(o->vstr);
+            o->vstr = NULL;
+            #else
+            vstr_clear(o->vstr);
+            o->vstr->alloc = 0;
+            o->vstr->len = 0;
+            o->pos = 0;
+            #endif
+            return 0;
         default:
             *errcode = MP_EINVAL;
             return MP_STREAM_ERROR;
@@ -159,24 +170,9 @@ STATIC mp_obj_t stringio_getvalue(mp_obj_t self_in) {
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_1(stringio_getvalue_obj, stringio_getvalue);
 
-STATIC mp_obj_t stringio_close(mp_obj_t self_in) {
-    mp_obj_stringio_t *self = MP_OBJ_TO_PTR(self_in);
-#if MICROPY_CPYTHON_COMPAT
-    vstr_free(self->vstr);
-    self->vstr = NULL;
-#else
-    vstr_clear(self->vstr);
-    self->vstr->alloc = 0;
-    self->vstr->len = 0;
-    self->pos = 0;
-#endif
-    return mp_const_none;
-}
-STATIC MP_DEFINE_CONST_FUN_OBJ_1(stringio_close_obj, stringio_close);
-
 STATIC mp_obj_t stringio___exit__(size_t n_args, const mp_obj_t *args) {
     (void)n_args;
-    return stringio_close(args[0]);
+    return mp_stream_close(args[0]);
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(stringio___exit___obj, 4, 4, stringio___exit__);
 
@@ -233,7 +229,7 @@ STATIC const mp_rom_map_elem_t stringio_locals_dict_table[] = {
     { MP_ROM_QSTR(MP_QSTR_write), MP_ROM_PTR(&mp_stream_write_obj) },
     { MP_ROM_QSTR(MP_QSTR_seek), MP_ROM_PTR(&mp_stream_seek_obj) },
     { MP_ROM_QSTR(MP_QSTR_flush), MP_ROM_PTR(&mp_stream_flush_obj) },
-    { MP_ROM_QSTR(MP_QSTR_close), MP_ROM_PTR(&stringio_close_obj) },
+    { MP_ROM_QSTR(MP_QSTR_close), MP_ROM_PTR(&mp_stream_close_obj) },
     { MP_ROM_QSTR(MP_QSTR_getvalue), MP_ROM_PTR(&stringio_getvalue_obj) },
     { MP_ROM_QSTR(MP_QSTR___enter__), MP_ROM_PTR(&mp_identity_obj) },
     { MP_ROM_QSTR(MP_QSTR___exit__), MP_ROM_PTR(&stringio___exit___obj) },
diff --git a/py/objstrunicode.c b/py/objstrunicode.c
index a243022a7..ca41a7baa 100644
--- a/py/objstrunicode.c
+++ b/py/objstrunicode.c
@@ -104,7 +104,7 @@ STATIC mp_obj_t uni_unary_op(mp_unary_op_t op, mp_obj_t self_in) {
         case MP_UNARY_OP_BOOL:
             return mp_obj_new_bool(str_len != 0);
         case MP_UNARY_OP_LEN:
-            return MP_OBJ_NEW_SMALL_INT(unichar_charlen((const char *)str_data, str_len));
+            return MP_OBJ_NEW_SMALL_INT(utf8_charlen(str_data, str_len));
         default:
             return MP_OBJ_NULL; // op not supported
     }
@@ -216,7 +216,7 @@ STATIC mp_obj_t str_subscr(mp_obj_t self_in, mp_obj_t index, mp_obj_t value) {
                 ++len;
             }
         }
-        return mp_obj_new_str((const char*)s, len, true); // This will create a one-character string
+        return mp_obj_new_str_via_qstr((const char*)s, len); // This will create a one-character string
     } else {
         return MP_OBJ_NULL; // op not supported
     }
@@ -291,7 +291,7 @@ STATIC mp_obj_t str_it_iternext(mp_obj_t self_in) {
     if (self->cur < len) {
         const byte *cur = str + self->cur;
         const byte *end = utf8_next_char(str + self->cur);
-        mp_obj_t o_out = mp_obj_new_str((const char*)cur, end - cur, true);
+        mp_obj_t o_out = mp_obj_new_str_via_qstr((const char*)cur, end - cur);
         self->cur += end - cur;
         return o_out;
     } else {
diff --git a/py/objtype.c b/py/objtype.c
index 5b70e8e48..dc9724e5b 100644
--- a/py/objtype.c
+++ b/py/objtype.c
@@ -3,7 +3,7 @@
  *
  * The MIT License (MIT)
  *
- * Copyright (c) 2013, 2014 Damien P. George
+ * Copyright (c) 2013-2018 Damien P. George
  * Copyright (c) 2014-2016 Paul Sokolovsky
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
@@ -42,19 +42,17 @@
 #define DEBUG_printf(...) (void)0
 #endif
 
+#define ENABLE_SPECIAL_ACCESSORS \
+    (MICROPY_PY_DESCRIPTORS  || MICROPY_PY_DELATTR_SETATTR || MICROPY_PY_BUILTINS_PROPERTY)
+
+#define TYPE_FLAG_IS_SUBCLASSED (0x0001)
+#define TYPE_FLAG_HAS_SPECIAL_ACCESSORS (0x0002)
+
 STATIC mp_obj_t static_class_method_make_new(const mp_obj_type_t *self_in, size_t n_args, size_t n_kw, const mp_obj_t *args);
 
 /******************************************************************************/
 // instance object
 
-STATIC mp_obj_t mp_obj_new_instance(const mp_obj_type_t *class, size_t subobjs) {
-    mp_obj_instance_t *o = m_new_obj_var(mp_obj_instance_t, mp_obj_t, subobjs);
-    o->base.type = class;
-    mp_map_init(&o->members, 0);
-    mp_seq_clear(o->subobj, 0, subobjs, sizeof(*o->subobj));
-    return MP_OBJ_FROM_PTR(o);
-}
-
 STATIC int instance_count_native_bases(const mp_obj_type_t *type, const mp_obj_type_t **last_native_base) {
     int count = 0;
     for (;;) {
@@ -68,6 +66,7 @@ STATIC int instance_count_native_bases(const mp_obj_type_t *type, const mp_obj_t
         } else if (type->parent == NULL) {
             // No parents so end search here.
             return count;
+        #if MICROPY_MULTIPLE_INHERITANCE
         } else if (((mp_obj_base_t*)type->parent)->type == &mp_type_tuple) {
             // Multiple parents, search through them all recursively.
             const mp_obj_tuple_t *parent_tuple = type->parent;
@@ -79,6 +78,7 @@ STATIC int instance_count_native_bases(const mp_obj_type_t *type, const mp_obj_t
                 count += instance_count_native_bases(bt, last_native_base);
             }
             return count;
+        #endif
         } else {
             // A single parent, use iteration to continue the search.
             type = type->parent;
@@ -86,6 +86,35 @@ STATIC int instance_count_native_bases(const mp_obj_type_t *type, const mp_obj_t
     }
 }
 
+// This wrapper function is allows a subclass of a native type to call the
+// __init__() method (corresponding to type->make_new) of the native type.
+STATIC mp_obj_t native_base_init_wrapper(size_t n_args, const mp_obj_t *args) {
+    mp_obj_instance_t *self = MP_OBJ_TO_PTR(args[0]);
+    const mp_obj_type_t *native_base = NULL;
+    instance_count_native_bases(self->base.type, &native_base);
+    self->subobj[0] = native_base->make_new(native_base, n_args - 1, 0, args + 1);
+    return mp_const_none;
+}
+STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(native_base_init_wrapper_obj, 1, MP_OBJ_FUN_ARGS_MAX, native_base_init_wrapper);
+
+#if !MICROPY_CPYTHON_COMPAT
+STATIC
+#endif
+mp_obj_instance_t *mp_obj_new_instance(const mp_obj_type_t *class, const mp_obj_type_t **native_base) {
+    size_t num_native_bases = instance_count_native_bases(class, native_base);
+    assert(num_native_bases < 2);
+    mp_obj_instance_t *o = m_new_obj_var(mp_obj_instance_t, mp_obj_t, num_native_bases);
+    o->base.type = class;
+    mp_map_init(&o->members, 0);
+    // Initialise the native base-class slot (should be 1 at most) with a valid
+    // object.  It doesn't matter which object, so long as it can be uniquely
+    // distinguished from a native class that is initialised.
+    if (num_native_bases != 0) {
+        o->subobj[0] = MP_OBJ_FROM_PTR(&native_base_init_wrapper_obj);
+    }
+    return o;
+}
+
 // TODO
 // This implements depth-first left-to-right MRO, which is not compliant with Python3 MRO
 // http://python-history.blogspot.com/2010/06/method-resolution-order.html
@@ -176,6 +205,7 @@ STATIC void mp_obj_class_lookup(struct class_lookup_data  *lookup, const mp_obj_
         if (type->parent == NULL) {
             DEBUG_printf("mp_obj_class_lookup: No more parents\n");
             return;
+        #if MICROPY_MULTIPLE_INHERITANCE
         } else if (((mp_obj_base_t*)type->parent)->type == &mp_type_tuple) {
             const mp_obj_tuple_t *parent_tuple = type->parent;
             const mp_obj_t *item = parent_tuple->items;
@@ -196,6 +226,7 @@ STATIC void mp_obj_class_lookup(struct class_lookup_data  *lookup, const mp_obj_
             // search last base (simple tail recursion elimination)
             assert(MP_OBJ_IS_TYPE(*item, &mp_type_type));
             type = (mp_obj_type_t*)MP_OBJ_TO_PTR(*item);
+        #endif
         } else {
             type = type->parent;
         }
@@ -251,20 +282,6 @@ STATIC void instance_print(const mp_print_t *print, mp_obj_t self_in, mp_print_k
 mp_obj_t mp_obj_instance_make_new(const mp_obj_type_t *self, size_t n_args, size_t n_kw, const mp_obj_t *args) {
     assert(mp_obj_is_instance_type(self));
 
-    const mp_obj_type_t *native_base;
-    size_t num_native_bases = instance_count_native_bases(self, &native_base);
-    assert(num_native_bases < 2);
-
-    mp_obj_instance_t *o = MP_OBJ_TO_PTR(mp_obj_new_instance(self, num_native_bases));
-
-    // This executes only "__new__" part of instance creation.
-    // TODO: This won't work well for classes with native bases.
-    // TODO: This is a hack, should be resolved along the lines of
-    // https://github.com/micropython/micropython/issues/606#issuecomment-43685883
-    if (n_args == 1 && *args == MP_OBJ_SENTINEL) {
-        return MP_OBJ_FROM_PTR(o);
-    }
-
     // look for __new__ function
     mp_obj_t init_fn[2] = {MP_OBJ_NULL};
     struct class_lookup_data lookup = {
@@ -276,13 +293,22 @@ mp_obj_t mp_obj_instance_make_new(const mp_obj_type_t *self, size_t n_args, size
     };
     mp_obj_class_lookup(&lookup, self);
 
-    mp_obj_t new_ret = MP_OBJ_FROM_PTR(o);
-    if (init_fn[0] == MP_OBJ_SENTINEL) {
-        // Native type's constructor is what wins - it gets all our arguments,
-        // and none Python classes are initialized at all.
-        o->subobj[0] = native_base->make_new(native_base, n_args, n_kw, args);
-    } else if (init_fn[0] != MP_OBJ_NULL) {
-        // now call Python class __new__ function with all args
+    const mp_obj_type_t *native_base = NULL;
+    mp_obj_instance_t *o;
+    if (init_fn[0] == MP_OBJ_NULL || init_fn[0] == MP_OBJ_SENTINEL) {
+        // Either there is no __new__() method defined or there is a native
+        // constructor.  In both cases create a blank instance.
+        o = mp_obj_new_instance(self, &native_base);
+
+        // Since type->make_new() implements both __new__() and __init__() in
+        // one go, of which the latter may be overridden by the Python subclass,
+        // we defer (see the end of this function) the call of the native
+        // constructor to give a chance for the Python __init__() method to call
+        // said native constructor.
+
+    } else {
+        // Call Python class __new__ function with all args to create an instance
+        mp_obj_t new_ret;
         if (n_args == 0 && n_kw == 0) {
             mp_obj_t args2[1] = {MP_OBJ_FROM_PTR(self)};
             new_ret = mp_call_function_n_kw(init_fn[0], 1, 0, args2);
@@ -294,17 +320,20 @@ mp_obj_t mp_obj_instance_make_new(const mp_obj_type_t *self, size_t n_args, size
             m_del(mp_obj_t, args2, 1 + n_args + 2 * n_kw);
         }
 
-    }
+        // https://docs.python.org/3.4/reference/datamodel.html#object.__new__
+        // "If __new__() does not return an instance of cls, then the new
+        // instance's __init__() method will not be invoked."
+        if (mp_obj_get_type(new_ret) != self) {
+            return new_ret;
+        }
 
-    // https://docs.python.org/3.4/reference/datamodel.html#object.__new__
-    // "If __new__() does not return an instance of cls, then the new instance's __init__() method will not be invoked."
-    if (mp_obj_get_type(new_ret) != self) {
-        return new_ret;
+        // The instance returned by __new__() becomes the new object
+        o = MP_OBJ_TO_PTR(new_ret);
     }
 
-    o = MP_OBJ_TO_PTR(new_ret);
-
     // now call Python class __init__ function with all args
+    // This method has a chance to call super().__init__() to construct a
+    // possible native base class.
     init_fn[0] = init_fn[1] = MP_OBJ_NULL;
     lookup.obj = o;
     lookup.attr = MP_QSTR___init__;
@@ -333,6 +362,12 @@ mp_obj_t mp_obj_instance_make_new(const mp_obj_type_t *self, size_t n_args, size
 
     }
 
+    // If the type had a native base that was not explicitly initialised
+    // (constructed) by the Python __init__() method then construct it now.
+    if (native_base != NULL && o->subobj[0] == MP_OBJ_FROM_PTR(&native_base_init_wrapper_obj)) {
+        o->subobj[0] = native_base->make_new(native_base, n_args, n_kw, args);
+    }
+
     return MP_OBJ_FROM_PTR(o);
 }
 
@@ -424,7 +459,7 @@ const byte mp_binary_op_method_name[MP_BINARY_OP_NUM_RUNTIME] = {
     [MP_BINARY_OP_LESS_EQUAL] = MP_QSTR___le__,
     [MP_BINARY_OP_MORE_EQUAL] = MP_QSTR___ge__,
     // MP_BINARY_OP_NOT_EQUAL, // a != b calls a == b and inverts result
-    [MP_BINARY_OP_IN] = MP_QSTR___contains__,
+    [MP_BINARY_OP_CONTAINS] = MP_QSTR___contains__,
 
     // All inplace methods are optional, and normal methods will be used
     // as a fallback.
@@ -537,7 +572,6 @@ STATIC void mp_obj_instance_load_attr(mp_obj_t self_in, qstr attr, mp_obj_t *des
     mp_map_elem_t *elem = mp_map_lookup(&self->members, MP_OBJ_NEW_QSTR(attr), MP_MAP_LOOKUP);
     if (elem != NULL) {
         // object member, always treated as a value
-        // TODO should we check for properties?
         dest[0] = elem->value;
         return;
     }
@@ -568,6 +602,11 @@ STATIC void mp_obj_instance_load_attr(mp_obj_t self_in, qstr attr, mp_obj_t *des
     mp_obj_t member = dest[0];
     if (member != MP_OBJ_NULL) {
         // changes here may may require changes to super_attr, below
+        if (!(self->base.type->flags & TYPE_FLAG_HAS_SPECIAL_ACCESSORS)) {
+            // Class doesn't have any special accessors to check so return straightaway
+            return;
+        }
+
         #if MICROPY_PY_BUILTINS_PROPERTY
         if (MP_OBJ_IS_TYPE(member, &mp_type_property)) {
             // object member is a property; delegate the load to the property
@@ -629,11 +668,15 @@ STATIC void mp_obj_instance_load_attr(mp_obj_t self_in, qstr attr, mp_obj_t *des
 STATIC bool mp_obj_instance_store_attr(mp_obj_t self_in, qstr attr, mp_obj_t value) {
     mp_obj_instance_t *self = MP_OBJ_TO_PTR(self_in);
 
+    if (!(self->base.type->flags & TYPE_FLAG_HAS_SPECIAL_ACCESSORS)) {
+        // Class doesn't have any special accessors so skip their checks
+        goto skip_special_accessors;
+    }
+
     #if MICROPY_PY_BUILTINS_PROPERTY || MICROPY_PY_DESCRIPTORS
     // With property and/or descriptors enabled we need to do a lookup
     // first in the class dict for the attribute to see if the store should
     // be delegated.
-    // Note: this makes all stores slow... how to fix?
     mp_obj_t member[2] = {MP_OBJ_NULL};
     struct class_lookup_data lookup = {
         .obj = self,
@@ -705,9 +748,9 @@ STATIC bool mp_obj_instance_store_attr(mp_obj_t self_in, qstr attr, mp_obj_t val
     }
     #endif
 
+    #if MICROPY_PY_DELATTR_SETATTR
     if (value == MP_OBJ_NULL) {
         // delete attribute
-        #if MICROPY_PY_DELATTR_SETATTR
         // try __delattr__ first
         mp_obj_t attr_delattr_method[3];
         mp_load_method_maybe(self_in, MP_QSTR___delattr__, attr_delattr_method);
@@ -717,13 +760,8 @@ STATIC bool mp_obj_instance_store_attr(mp_obj_t self_in, qstr attr, mp_obj_t val
             mp_call_method_n_kw(1, 0, attr_delattr_method);
             return true;
         }
-        #endif
-
-        mp_map_elem_t *elem = mp_map_lookup(&self->members, MP_OBJ_NEW_QSTR(attr), MP_MAP_LOOKUP_REMOVE_IF_FOUND);
-        return elem != NULL;
     } else {
         // store attribute
-        #if MICROPY_PY_DELATTR_SETATTR
         // try __setattr__ first
         mp_obj_t attr_setattr_method[4];
         mp_load_method_maybe(self_in, MP_QSTR___setattr__, attr_setattr_method);
@@ -734,14 +772,23 @@ STATIC bool mp_obj_instance_store_attr(mp_obj_t self_in, qstr attr, mp_obj_t val
             mp_call_method_n_kw(2, 0, attr_setattr_method);
             return true;
         }
-        #endif
+    }
+    #endif
 
+skip_special_accessors:
+
+    if (value == MP_OBJ_NULL) {
+        // delete attribute
+        mp_map_elem_t *elem = mp_map_lookup(&self->members, MP_OBJ_NEW_QSTR(attr), MP_MAP_LOOKUP_REMOVE_IF_FOUND);
+        return elem != NULL;
+    } else {
+        // store attribute
         mp_map_lookup(&self->members, MP_OBJ_NEW_QSTR(attr), MP_MAP_LOOKUP_ADD_IF_NOT_FOUND)->value = value;
         return true;
     }
 }
 
-void mp_obj_instance_attr(mp_obj_t self_in, qstr attr, mp_obj_t *dest) {
+STATIC void mp_obj_instance_attr(mp_obj_t self_in, qstr attr, mp_obj_t *dest) {
     if (dest[0] == MP_OBJ_NULL) {
         mp_obj_instance_load_attr(self_in, attr, dest);
     } else {
@@ -876,6 +923,34 @@ STATIC mp_int_t instance_get_buffer(mp_obj_t self_in, mp_buffer_info_t *bufinfo,
 //  - there is a constant mp_obj_type_t (called mp_type_type) for the 'type' object
 //  - creating a new class (a new type) creates a new mp_obj_type_t
 
+#if ENABLE_SPECIAL_ACCESSORS
+STATIC bool check_for_special_accessors(mp_obj_t key, mp_obj_t value) {
+    #if MICROPY_PY_DELATTR_SETATTR
+    if (key == MP_OBJ_NEW_QSTR(MP_QSTR___setattr__) || key == MP_OBJ_NEW_QSTR(MP_QSTR___delattr__)) {
+        return true;
+    }
+    #endif
+    #if MICROPY_PY_BUILTINS_PROPERTY
+    if (MP_OBJ_IS_TYPE(value, &mp_type_property)) {
+        return true;
+    }
+    #endif
+    #if MICROPY_PY_DESCRIPTORS
+    static const uint8_t to_check[] = {
+        MP_QSTR___get__, MP_QSTR___set__, MP_QSTR___delete__,
+    };
+    for (size_t i = 0; i < MP_ARRAY_SIZE(to_check); ++i) {
+        mp_obj_t dest_temp[2];
+        mp_load_method_protected(value, to_check[i], dest_temp, true);
+        if (dest_temp[0] != MP_OBJ_NULL) {
+            return true;
+        }
+    }
+    #endif
+    return false;
+}
+#endif
+
 STATIC void type_print(const mp_print_t *print, mp_obj_t self_in, mp_print_kind_t kind) {
     (void)kind;
     mp_obj_type_t *self = MP_OBJ_TO_PTR(self_in);
@@ -950,21 +1025,34 @@ STATIC void type_attr(mp_obj_t self_in, qstr attr, mp_obj_t *dest) {
         if (self->locals_dict != NULL) {
             assert(self->locals_dict->base.type == &mp_type_dict); // MicroPython restriction, for now
             mp_map_t *locals_map = &self->locals_dict->map;
+            if (locals_map->is_fixed) {
+                // can't apply delete/store to a fixed map
+                return;
+            }
             if (dest[1] == MP_OBJ_NULL) {
                 // delete attribute
                 mp_map_elem_t *elem = mp_map_lookup(locals_map, MP_OBJ_NEW_QSTR(attr), MP_MAP_LOOKUP_REMOVE_IF_FOUND);
-                // note that locals_map may be in ROM, so remove will fail in that case
                 if (elem != NULL) {
                     dest[0] = MP_OBJ_NULL; // indicate success
                 }
             } else {
+                #if ENABLE_SPECIAL_ACCESSORS
+                // Check if we add any special accessor methods with this store
+                if (!(self->flags & TYPE_FLAG_HAS_SPECIAL_ACCESSORS)) {
+                    if (check_for_special_accessors(MP_OBJ_NEW_QSTR(attr), dest[1])) {
+                        if (self->flags & TYPE_FLAG_IS_SUBCLASSED) {
+                            // This class is already subclassed so can't have special accessors added
+                            mp_raise_msg(&mp_type_AttributeError, "can't add special method to already-subclassed class");
+                        }
+                        self->flags |= TYPE_FLAG_HAS_SPECIAL_ACCESSORS;
+                    }
+                }
+                #endif
+
                 // store attribute
                 mp_map_elem_t *elem = mp_map_lookup(locals_map, MP_OBJ_NEW_QSTR(attr), MP_MAP_LOOKUP_ADD_IF_NOT_FOUND);
-                // note that locals_map may be in ROM, so add will fail in that case
-                if (elem != NULL) {
-                    elem->value = make_obj_long_lived(dest[1], 10);
-                    dest[0] = MP_OBJ_NULL; // indicate success
-                }
+                elem->value = make_obj_long_lived(dest[1], 10);
+                dest[0] = MP_OBJ_NULL; // indicate success
             }
         }
     }
@@ -981,26 +1069,26 @@ const mp_obj_type_t mp_type_type = {
 };
 
 mp_obj_t mp_obj_new_type(qstr name, mp_obj_t bases_tuple, mp_obj_t locals_dict) {
-    if(!MP_OBJ_IS_TYPE(bases_tuple, &mp_type_tuple)) {
-        // MicroPython restriction, for now
-        mp_raise_TypeError("type() argument 2 must be tuple");
+    // Verify input objects have expected type
+    if (!MP_OBJ_IS_TYPE(bases_tuple, &mp_type_tuple)) {
+        mp_raise_TypeError(NULL);
     }
-    if(!MP_OBJ_IS_TYPE(locals_dict, &mp_type_dict)) {
-        // MicroPython restriction, for now
-        mp_raise_TypeError("type() argument 3 must be dict");
+    if (!MP_OBJ_IS_TYPE(locals_dict, &mp_type_dict)) {
+        mp_raise_TypeError(NULL);
     }
 
     // TODO might need to make a copy of locals_dict; at least that's how CPython does it
 
     // Basic validation of base classes
-    size_t len;
-    mp_obj_t *items;
-    mp_obj_tuple_get(bases_tuple, &len, &items);
-    for (size_t i = 0; i < len; i++) {
-        if(!MP_OBJ_IS_TYPE(items[i], &mp_type_type)) {
+    uint16_t base_flags = 0;
+    size_t bases_len;
+    mp_obj_t *bases_items;
+    mp_obj_tuple_get(bases_tuple, &bases_len, &bases_items);
+    for (size_t i = 0; i < bases_len; i++) {
+        if (!MP_OBJ_IS_TYPE(bases_items[i], &mp_type_type)) {
             mp_raise_TypeError("type is not an acceptable base type");
         }
-        mp_obj_type_t *t = MP_OBJ_TO_PTR(items[i]);
+        mp_obj_type_t *t = MP_OBJ_TO_PTR(bases_items[i]);
         // TODO: Verify with CPy, tested on function type
         if (t->make_new == NULL) {
             if (MICROPY_ERROR_REPORTING == MICROPY_ERROR_REPORTING_TERSE) {
@@ -1010,10 +1098,17 @@ mp_obj_t mp_obj_new_type(qstr name, mp_obj_t bases_tuple, mp_obj_t locals_dict)
                     "type '%q' is not an acceptable base type", t->name);
             }
         }
+        #if ENABLE_SPECIAL_ACCESSORS
+        if (mp_obj_is_instance_type(t)) {
+            t->flags |= TYPE_FLAG_IS_SUBCLASSED;
+            base_flags |= t->flags & TYPE_FLAG_HAS_SPECIAL_ACCESSORS;
+        }
+        #endif
     }
 
     mp_obj_type_t *o = m_new0_ll(mp_obj_type_t, 1);
     o->base.type = &mp_type_type;
+    o->flags = base_flags;
     o->name = name;
     o->print = instance_print;
     o->make_new = mp_obj_instance_make_new;
@@ -1026,22 +1121,41 @@ mp_obj_t mp_obj_new_type(qstr name, mp_obj_t bases_tuple, mp_obj_t locals_dict)
     //o->iternext = ; not implemented
     o->buffer_p.get_buffer = instance_get_buffer;
 
-    if (len > 0) {
+    if (bases_len > 0) {
         // Inherit protocol from a base class. This allows to define an
         // abstract base class which would translate C-level protocol to
         // Python method calls, and any subclass inheriting from it will
         // support this feature.
-        o->protocol = ((mp_obj_type_t*)MP_OBJ_TO_PTR(items[0]))->protocol;
+        o->protocol = ((mp_obj_type_t*)MP_OBJ_TO_PTR(bases_items[0]))->protocol;
 
-        if (len >= 2) {
+        if (bases_len >= 2) {
+            #if MICROPY_MULTIPLE_INHERITANCE
             o->parent = MP_OBJ_TO_PTR(bases_tuple);
+            #else
+            mp_raise_NotImplementedError("multiple inheritance not supported");
+            #endif
         } else {
-            o->parent = MP_OBJ_TO_PTR(items[0]);
+            o->parent = MP_OBJ_TO_PTR(bases_items[0]);
         }
     }
 
     o->locals_dict = make_dict_long_lived(locals_dict, 10);
 
+    #if ENABLE_SPECIAL_ACCESSORS
+    // Check if the class has any special accessor methods
+    if (!(o->flags & TYPE_FLAG_HAS_SPECIAL_ACCESSORS)) {
+        for (size_t i = 0; i < o->locals_dict->map.alloc; i++) {
+            if (MP_MAP_SLOT_IS_FILLED(&o->locals_dict->map, i)) {
+                const mp_map_elem_t *elem = &o->locals_dict->map.table[i];
+                if (check_for_special_accessors(elem->key, elem->value)) {
+                    o->flags |= TYPE_FLAG_HAS_SPECIAL_ACCESSORS;
+                    break;
+                }
+            }
+        }
+    }
+    #endif
+
     const mp_obj_type_t *native_base;
     size_t num_native_bases = instance_count_native_bases(o, &native_base);
     if (num_native_bases > 1) {
@@ -1114,49 +1228,69 @@ STATIC void super_attr(mp_obj_t self_in, qstr attr, mp_obj_t *dest) {
         .is_type = false,
     };
 
+    // Allow a call super().__init__() to reach any native base classes
+    if (attr == MP_QSTR___init__) {
+        lookup.meth_offset = offsetof(mp_obj_type_t, make_new);
+    }
+
     if (type->parent == NULL) {
         // no parents, do nothing
+    #if MICROPY_MULTIPLE_INHERITANCE
     } else if (((mp_obj_base_t*)type->parent)->type == &mp_type_tuple) {
         const mp_obj_tuple_t *parent_tuple = type->parent;
         size_t len = parent_tuple->len;
         const mp_obj_t *items = parent_tuple->items;
         for (size_t i = 0; i < len; i++) {
             assert(MP_OBJ_IS_TYPE(items[i], &mp_type_type));
+            if (MP_OBJ_TO_PTR(items[i]) == &mp_type_object) {
+                // The "object" type will be searched at the end of this function,
+                // and we don't want to lookup native methods in object.
+                continue;
+            }
             mp_obj_class_lookup(&lookup, (mp_obj_type_t*)MP_OBJ_TO_PTR(items[i]));
             if (dest[0] != MP_OBJ_NULL) {
                 break;
             }
         }
-    } else {
+    #endif
+    } else if (type->parent != &mp_type_object) {
         mp_obj_class_lookup(&lookup, type->parent);
     }
 
     if (dest[0] != MP_OBJ_NULL) {
-        mp_obj_t member = dest[0];
-        // changes to mp_obj_instance_load_attr may require changes
-        // here...
-        #if MICROPY_PY_BUILTINS_PROPERTY
-        if (MP_OBJ_IS_TYPE(member, &mp_type_property)) {
-            const mp_obj_t *proxy = mp_obj_property_get(member);
-            if (proxy[0] == mp_const_none) {
-                mp_raise_AttributeError("unreadable attribute");
-            } else {
-                dest[0] = mp_call_function_n_kw(proxy[0], 1, 0, &self_in);
+        if (dest[0] == MP_OBJ_SENTINEL) {
+            // Looked up native __init__ so defer to it
+            dest[0] = MP_OBJ_FROM_PTR(&native_base_init_wrapper_obj);
+            dest[1] = self->obj;
+        } else {
+            mp_obj_t member = dest[0];
+            // changes to mp_obj_instance_load_attr may require changes
+            // here...
+            #if MICROPY_PY_BUILTINS_PROPERTY
+            if (MP_OBJ_IS_TYPE(member, &mp_type_property)) {
+                const mp_obj_t *proxy = mp_obj_property_get(member);
+                if (proxy[0] == mp_const_none) {
+                    mp_raise_AttributeError("unreadable attribute");
+                } else {
+                    dest[0] = mp_call_function_n_kw(proxy[0], 1, 0, &self_in);
+                }
             }
+            #endif
+            #if MICROPY_PY_DESCRIPTORS
+            mp_obj_t attr_get_method[4];
+            mp_load_method_maybe(member, MP_QSTR___get__, attr_get_method);
+            if (attr_get_method[0] != MP_OBJ_NULL) {
+                attr_get_method[2] = self_in;
+                attr_get_method[3] = MP_OBJ_FROM_PTR(mp_obj_get_type(self_in));
+                dest[0] = mp_call_method_n_kw(2, 0, attr_get_method);
         }
-        #endif
-        #if MICROPY_PY_DESCRIPTORS
-        mp_obj_t attr_get_method[4];
-        mp_load_method_maybe(member, MP_QSTR___get__, attr_get_method);
-        if (attr_get_method[0] != MP_OBJ_NULL) {
-            attr_get_method[2] = self_in;
-            attr_get_method[3] = MP_OBJ_FROM_PTR(mp_obj_get_type(self_in));
-            dest[0] = mp_call_method_n_kw(2, 0, attr_get_method);
-        }
-        #endif
         return;
     }
 
+    // Reset meth_offset so we don't look up any native methods in object,
+    // because object never takes up the native base-class slot.
+    lookup.meth_offset = 0;
+
     mp_obj_class_lookup(&lookup, &mp_type_object);
 }
 
@@ -1196,6 +1330,7 @@ bool mp_obj_is_subclass_fast(mp_const_obj_t object, mp_const_obj_t classinfo) {
         if (self->parent == NULL) {
             // type has no parents
             return false;
+        #if MICROPY_MULTIPLE_INHERITANCE
         } else if (((mp_obj_base_t*)self->parent)->type == &mp_type_tuple) {
             // get the base objects (they should be type objects)
             const mp_obj_tuple_t *parent_tuple = self->parent;
@@ -1211,6 +1346,7 @@ bool mp_obj_is_subclass_fast(mp_const_obj_t object, mp_const_obj_t classinfo) {
 
             // search last base (simple tail recursion elimination)
             object = *item;
+        #endif
         } else {
             // type has 1 parent
             object = MP_OBJ_FROM_PTR(self->parent);
diff --git a/py/objtype.h b/py/objtype.h
index 52419f3cd..3fc8c6e1b 100644
--- a/py/objtype.h
+++ b/py/objtype.h
@@ -37,8 +37,10 @@ typedef struct _mp_obj_instance_t {
     // TODO maybe cache __getattr__ and __setattr__ for efficient lookup of them
 } mp_obj_instance_t;
 
-// this needs to be exposed for MICROPY_OPT_CACHE_MAP_LOOKUP_IN_BYTECODE to work
-void mp_obj_instance_attr(mp_obj_t self_in, qstr attr, mp_obj_t *dest);
+#if MICROPY_CPYTHON_COMPAT
+// this is needed for object.__new__
+mp_obj_instance_t *mp_obj_new_instance(const mp_obj_type_t *cls, const mp_obj_type_t **native_base);
+#endif
 
 // these need to be exposed so mp_obj_is_callable can work correctly
 bool mp_obj_instance_is_callable(mp_obj_t self_in);
diff --git a/py/opmethods.c b/py/opmethods.c
index 1200ba39e..247fa5bbc 100644
--- a/py/opmethods.c
+++ b/py/opmethods.c
@@ -24,7 +24,7 @@
  * THE SOFTWARE.
  */
 
-#include "py/runtime0.h"
+#include "py/obj.h"
 #include "py/builtin.h"
 
 STATIC mp_obj_t op_getitem(mp_obj_t self_in, mp_obj_t key_in) {
@@ -47,6 +47,6 @@ MP_DEFINE_CONST_FUN_OBJ_2(mp_op_delitem_obj, op_delitem);
 
 STATIC mp_obj_t op_contains(mp_obj_t lhs_in, mp_obj_t rhs_in) {
     mp_obj_type_t *type = mp_obj_get_type(lhs_in);
-    return type->binary_op(MP_BINARY_OP_IN, lhs_in, rhs_in);
+    return type->binary_op(MP_BINARY_OP_CONTAINS, lhs_in, rhs_in);
 }
 MP_DEFINE_CONST_FUN_OBJ_2(mp_op_contains_obj, op_contains);
diff --git a/py/parse.c b/py/parse.c
index 08a403401..ab162710d 100644
--- a/py/parse.c
+++ b/py/parse.c
@@ -3,7 +3,7 @@
  *
  * The MIT License (MIT)
  *
- * Copyright (c) 2013-2015 Damien P. George
+ * Copyright (c) 2013-2017 Damien P. George
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -58,15 +58,6 @@
 // (un)comment to use rule names; for debugging
 //#define USE_RULE_NAME (1)
 
-typedef struct _rule_t {
-    byte rule_id;
-    byte act;
-#ifdef USE_RULE_NAME
-    const char *rule_name;
-#endif
-    uint16_t arg[];
-} rule_t;
-
 enum {
 // define rules with a compile function
 #define DEF_RULE(rule, comp, kind, ...) RULE_##rule,
@@ -84,6 +75,8 @@ enum {
 #undef DEF_RULE_NC
 };
 
+// Define an array of actions corresponding to each rule
+STATIC const uint8_t rule_act_table[] = {
 #define or(n)                   (RULE_ACT_OR | n)
 #define and(n)                  (RULE_ACT_AND | n)
 #define and_ident(n)            (RULE_ACT_AND | n | RULE_ACT_ALLOW_IDENT)
@@ -91,44 +84,128 @@ enum {
 #define one_or_more             (RULE_ACT_LIST | 2)
 #define list                    (RULE_ACT_LIST | 1)
 #define list_with_end           (RULE_ACT_LIST | 3)
-#define tok(t)                  (RULE_ARG_TOK | MP_TOKEN_##t)
-#define rule(r)                 (RULE_ARG_RULE | RULE_##r)
-#define opt_rule(r)             (RULE_ARG_OPT_RULE | RULE_##r)
-#ifdef USE_RULE_NAME
-#define DEF_RULE(rule, comp, kind, ...) static const rule_t rule_##rule = { RULE_##rule, kind, #rule, { __VA_ARGS__ } };
-#define DEF_RULE_NC(rule, kind, ...) static const rule_t rule_##rule = { RULE_##rule, kind, #rule, { __VA_ARGS__ } };
-#else
-#define DEF_RULE(rule, comp, kind, ...) static const rule_t rule_##rule = { RULE_##rule, kind, { __VA_ARGS__ } };
-#define DEF_RULE_NC(rule, kind, ...) static const rule_t rule_##rule = { RULE_##rule, kind, { __VA_ARGS__ } };
-#endif
+
+#define DEF_RULE(rule, comp, kind, ...) kind,
+#define DEF_RULE_NC(rule, kind, ...)
+#include "py/grammar.h"
+#undef DEF_RULE
+#undef DEF_RULE_NC
+
+    0, // RULE_const_object
+
+#define DEF_RULE(rule, comp, kind, ...)
+#define DEF_RULE_NC(rule, kind, ...) kind,
 #include "py/grammar.h"
+#undef DEF_RULE
+#undef DEF_RULE_NC
+
 #undef or
 #undef and
+#undef and_ident
+#undef and_blank
+#undef one_or_more
 #undef list
 #undef list_with_end
+};
+
+// Define the argument data for each rule, as a combined array
+STATIC const uint16_t rule_arg_combined_table[] = {
+#define tok(t)                  (RULE_ARG_TOK | MP_TOKEN_##t)
+#define rule(r)                 (RULE_ARG_RULE | RULE_##r)
+#define opt_rule(r)             (RULE_ARG_OPT_RULE | RULE_##r)
+
+#define DEF_RULE(rule, comp, kind, ...) __VA_ARGS__,
+#define DEF_RULE_NC(rule, kind, ...)
+#include "py/grammar.h"
+#undef DEF_RULE
+#undef DEF_RULE_NC
+
+#define DEF_RULE(rule, comp, kind, ...)
+#define DEF_RULE_NC(rule, kind, ...)  __VA_ARGS__,
+#include "py/grammar.h"
+#undef DEF_RULE
+#undef DEF_RULE_NC
+
 #undef tok
 #undef rule
 #undef opt_rule
-#undef one_or_more
+};
+
+// Macro to create a list of N identifiers where N is the number of variable arguments to the macro
+#define RULE_EXPAND(x) x
+#define RULE_PADDING(rule, ...) RULE_PADDING2(rule, __VA_ARGS__, RULE_PADDING_IDS(rule))
+#define RULE_PADDING2(rule, ...) RULE_EXPAND(RULE_PADDING3(rule, __VA_ARGS__))
+#define RULE_PADDING3(rule, _1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, _12, ...) __VA_ARGS__
+#define RULE_PADDING_IDS(r) PAD12_##r, PAD11_##r, PAD10_##r, PAD9_##r, PAD8_##r, PAD7_##r, PAD6_##r, PAD5_##r, PAD4_##r, PAD3_##r, PAD2_##r, PAD1_##r,
+
+// Use an enum to create constants specifying how much room a rule takes in rule_arg_combined_table
+enum {
+#define DEF_RULE(rule, comp, kind, ...) RULE_PADDING(rule, __VA_ARGS__)
+#define DEF_RULE_NC(rule, kind, ...)
+#include "py/grammar.h"
+#undef DEF_RULE
+#undef DEF_RULE_NC
+#define DEF_RULE(rule, comp, kind, ...)
+#define DEF_RULE_NC(rule, kind, ...) RULE_PADDING(rule, __VA_ARGS__)
+#include "py/grammar.h"
 #undef DEF_RULE
 #undef DEF_RULE_NC
+};
 
-STATIC const rule_t *const rules[] = {
-// define rules with a compile function
-#define DEF_RULE(rule, comp, kind, ...) &rule_##rule,
+// Macro to compute the start of a rule in rule_arg_combined_table
+#define RULE_ARG_OFFSET(rule, ...) RULE_ARG_OFFSET2(rule, __VA_ARGS__, RULE_ARG_OFFSET_IDS(rule))
+#define RULE_ARG_OFFSET2(rule, ...) RULE_EXPAND(RULE_ARG_OFFSET3(rule, __VA_ARGS__))
+#define RULE_ARG_OFFSET3(rule, _1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, _12, _13, ...) _13
+#define RULE_ARG_OFFSET_IDS(r) PAD12_##r, PAD11_##r, PAD10_##r, PAD9_##r, PAD8_##r, PAD7_##r, PAD6_##r, PAD5_##r, PAD4_##r, PAD3_##r, PAD2_##r, PAD1_##r, PAD0_##r,
+
+// Use the above enum values to create a table of offsets for each rule's arg
+// data, which indexes rule_arg_combined_table.  The offsets require 9 bits of
+// storage but only the lower 8 bits are stored here.  The 9th bit is computed
+// in get_rule_arg using the FIRST_RULE_WITH_OFFSET_ABOVE_255 constant.
+STATIC const uint8_t rule_arg_offset_table[] = {
+#define DEF_RULE(rule, comp, kind, ...) RULE_ARG_OFFSET(rule, __VA_ARGS__) & 0xff,
 #define DEF_RULE_NC(rule, kind, ...)
 #include "py/grammar.h"
 #undef DEF_RULE
 #undef DEF_RULE_NC
-    NULL, // RULE_const_object
+    0, // RULE_const_object
+#define DEF_RULE(rule, comp, kind, ...)
+#define DEF_RULE_NC(rule, kind, ...) RULE_ARG_OFFSET(rule, __VA_ARGS__) & 0xff,
+#include "py/grammar.h"
+#undef DEF_RULE
+#undef DEF_RULE_NC
+};
 
-// define rules without a compile function
+// Define a constant that's used to determine the 9th bit of the values in rule_arg_offset_table
+static const size_t FIRST_RULE_WITH_OFFSET_ABOVE_255 =
+#define DEF_RULE(rule, comp, kind, ...) RULE_ARG_OFFSET(rule, __VA_ARGS__) >= 0x100 ? RULE_##rule :
+#define DEF_RULE_NC(rule, kind, ...)
+#include "py/grammar.h"
+#undef DEF_RULE
+#undef DEF_RULE_NC
+#define DEF_RULE(rule, comp, kind, ...)
+#define DEF_RULE_NC(rule, kind, ...) RULE_ARG_OFFSET(rule, __VA_ARGS__) >= 0x100 ? RULE_##rule :
+#include "py/grammar.h"
+#undef DEF_RULE
+#undef DEF_RULE_NC
+0;
+
+#if USE_RULE_NAME
+// Define an array of rule names corresponding to each rule
+STATIC const char *const rule_name_table[] = {
+#define DEF_RULE(rule, comp, kind, ...) #rule,
+#define DEF_RULE_NC(rule, kind, ...)
+#include "py/grammar.h"
+#undef DEF_RULE
+#undef DEF_RULE_NC
+    "", // RULE_const_object
 #define DEF_RULE(rule, comp, kind, ...)
-#define DEF_RULE_NC(rule, kind, ...) &rule_##rule,
+#define DEF_RULE_NC(rule, kind, ...) #rule,
 #include "py/grammar.h"
 #undef DEF_RULE
 #undef DEF_RULE_NC
 };
+#endif
 
 typedef struct _rule_stack_t {
     size_t src_line : 8 * sizeof(size_t) - 8; // maximum bits storing source line number
@@ -164,8 +241,17 @@ typedef struct _parser_t {
     #endif
 } parser_t;
 
+STATIC const uint16_t *get_rule_arg(uint8_t r_id) {
+    size_t off = rule_arg_offset_table[r_id];
+    if (r_id >= FIRST_RULE_WITH_OFFSET_ABOVE_255) {
+        off |= 0x100;
+    }
+    return &rule_arg_combined_table[off];
+}
+
 #pragma GCC diagnostic push
 #pragma GCC diagnostic ignored "-Wcast-align"
+
 STATIC void *parser_alloc(parser_t *parser, size_t num_bytes) {
     // use a custom memory allocator to store parse nodes sequentially in large chunks
 
@@ -208,7 +294,7 @@ STATIC void *parser_alloc(parser_t *parser, size_t num_bytes) {
 }
 #pragma GCC diagnostic pop
 
-STATIC void push_rule(parser_t *parser, size_t src_line, const rule_t *rule, size_t arg_i) {
+STATIC void push_rule(parser_t *parser, size_t src_line, uint8_t rule_id, size_t arg_i) {
     if (parser->rule_stack_top >= parser->rule_stack_alloc) {
         rule_stack_t *rs = m_renew(rule_stack_t, parser->rule_stack, parser->rule_stack_alloc, parser->rule_stack_alloc + MICROPY_ALLOC_PARSE_RULE_INC);
         parser->rule_stack = rs;
@@ -216,21 +302,22 @@ STATIC void push_rule(parser_t *parser, size_t src_line, const rule_t *rule, siz
     }
     rule_stack_t *rs = &parser->rule_stack[parser->rule_stack_top++];
     rs->src_line = src_line;
-    rs->rule_id = rule->rule_id;
+    rs->rule_id = rule_id;
     rs->arg_i = arg_i;
 }
 
 STATIC void push_rule_from_arg(parser_t *parser, size_t arg) {
     assert((arg & RULE_ARG_KIND_MASK) == RULE_ARG_RULE || (arg & RULE_ARG_KIND_MASK) == RULE_ARG_OPT_RULE);
     size_t rule_id = arg & RULE_ARG_ARG_MASK;
-    push_rule(parser, parser->lexer->tok_line, rules[rule_id], 0);
+    push_rule(parser, parser->lexer->tok_line, rule_id, 0);
 }
 
-STATIC void pop_rule(parser_t *parser, const rule_t **rule, size_t *arg_i, size_t *src_line) {
+STATIC uint8_t pop_rule(parser_t *parser, size_t *arg_i, size_t *src_line) {
     parser->rule_stack_top -= 1;
-    *rule = rules[parser->rule_stack[parser->rule_stack_top].rule_id];
+    uint8_t rule_id = parser->rule_stack[parser->rule_stack_top].rule_id;
     *arg_i = parser->rule_stack[parser->rule_stack_top].arg_i;
     *src_line = parser->rule_stack[parser->rule_stack_top].src_line;
+    return rule_id;
 }
 
 bool mp_parse_node_is_const_false(mp_parse_node_t pn) {
@@ -316,11 +403,11 @@ void mp_parse_node_print(mp_parse_node_t pn, size_t indent) {
             #endif
         } else {
             size_t n = MP_PARSE_NODE_STRUCT_NUM_NODES(pns);
-#ifdef USE_RULE_NAME
-            printf("%s(%u) (n=%u)\n", rules[MP_PARSE_NODE_STRUCT_KIND(pns)]->rule_name, (uint)MP_PARSE_NODE_STRUCT_KIND(pns), (uint)n);
-#else
+            #if USE_RULE_NAME
+            printf("%s(%u) (n=%u)\n", rule_name_table[MP_PARSE_NODE_STRUCT_KIND(pns)], (uint)MP_PARSE_NODE_STRUCT_KIND(pns), (uint)n);
+            #else
             printf("rule(%u) (n=%u)\n", (uint)MP_PARSE_NODE_STRUCT_KIND(pns), (uint)n);
-#endif
+            #endif
             for (size_t i = 0; i < n; i++) {
                 mp_parse_node_print(pns->nodes[i], indent + 2);
             }
@@ -372,7 +459,19 @@ STATIC mp_parse_node_t make_node_const_object(parser_t *parser, size_t src_line,
     return (mp_parse_node_t)pn;
 }
 
-STATIC void push_result_token(parser_t *parser, const rule_t *rule) {
+STATIC mp_parse_node_t mp_parse_node_new_small_int_checked(parser_t *parser, mp_obj_t o_val) {
+    (void)parser;
+    mp_int_t val = MP_OBJ_SMALL_INT_VALUE(o_val);
+    #if MICROPY_OBJ_REPR == MICROPY_OBJ_REPR_D
+    // A parse node is only 32-bits and the small-int value must fit in 31-bits
+    if (((val ^ (val << 1)) & 0xffffffff80000000) != 0) {
+        return make_node_const_object(parser, 0, o_val);
+    }
+    #endif
+    return mp_parse_node_new_small_int(val);
+}
+
+STATIC void push_result_token(parser_t *parser, uint8_t rule_id) {
     mp_parse_node_t pn;
     mp_lexer_t *lex = parser->lexer;
     if (lex->tok_kind == MP_TOKEN_NAME) {
@@ -380,10 +479,10 @@ STATIC void push_result_token(parser_t *parser, const rule_t *rule) {
         #if MICROPY_COMP_CONST
         // if name is a standalone identifier, look it up in the table of dynamic constants
         mp_map_elem_t *elem;
-        if (rule->rule_id == RULE_atom
+        if (rule_id == RULE_atom
             && (elem = mp_map_lookup(&parser->consts, MP_OBJ_NEW_QSTR(id), MP_MAP_LOOKUP)) != NULL) {
             if (MP_OBJ_IS_SMALL_INT(elem->value)) {
-                pn = mp_parse_node_new_small_int(MP_OBJ_SMALL_INT_VALUE(elem->value));
+                pn = mp_parse_node_new_small_int_checked(parser, elem->value);
             } else {
                 pn = make_node_const_object(parser, lex->tok_line, elem->value);
             }
@@ -391,13 +490,13 @@ STATIC void push_result_token(parser_t *parser, const rule_t *rule) {
             pn = mp_parse_node_new_leaf(MP_PARSE_NODE_ID, id);
         }
         #else
-        (void)rule;
+        (void)rule_id;
         pn = mp_parse_node_new_leaf(MP_PARSE_NODE_ID, id);
         #endif
     } else if (lex->tok_kind == MP_TOKEN_INTEGER) {
         mp_obj_t o = mp_parse_num_integer(lex->vstr.buf, lex->vstr.len, 0, lex);
         if (MP_OBJ_IS_SMALL_INT(o)) {
-            pn = mp_parse_node_new_small_int(MP_OBJ_SMALL_INT_VALUE(o));
+            pn = mp_parse_node_new_small_int_checked(parser, o);
         } else {
             pn = make_node_const_object(parser, lex->tok_line, o);
         }
@@ -420,7 +519,7 @@ STATIC void push_result_token(parser_t *parser, const rule_t *rule) {
             pn = mp_parse_node_new_leaf(lex->tok_kind == MP_TOKEN_STRING ? MP_PARSE_NODE_STRING : MP_PARSE_NODE_BYTES, qst);
         } else {
             // not interned, make a node holding a pointer to the string/bytes object
-            mp_obj_t o = mp_obj_new_str_of_type(
+            mp_obj_t o = mp_obj_new_str_copy(
                 lex->tok_kind == MP_TOKEN_STRING ? &mp_type_str : &mp_type_bytes,
                 (const byte*)lex->vstr.buf, lex->vstr.len);
             pn = make_node_const_object(parser, lex->tok_line, o);
@@ -445,12 +544,12 @@ STATIC const mp_rom_map_elem_t mp_constants_table[] = {
 STATIC MP_DEFINE_CONST_MAP(mp_constants_map, mp_constants_table);
 #endif
 
-STATIC void push_result_rule(parser_t *parser, size_t src_line, const rule_t *rule, size_t num_args);
+STATIC void push_result_rule(parser_t *parser, size_t src_line, uint8_t rule_id, size_t num_args);
 
 #if MICROPY_COMP_CONST_FOLDING
-STATIC bool fold_logical_constants(parser_t *parser, const rule_t *rule, size_t *num_args) {
-    if (rule->rule_id == RULE_or_test
-        || rule->rule_id == RULE_and_test) {
+STATIC bool fold_logical_constants(parser_t *parser, uint8_t rule_id, size_t *num_args) {
+    if (rule_id == RULE_or_test
+        || rule_id == RULE_and_test) {
         // folding for binary logical ops: or and
         size_t copy_to = *num_args;
         for (size_t i = copy_to; i > 0;) {
@@ -460,7 +559,7 @@ STATIC bool fold_logical_constants(parser_t *parser, const rule_t *rule, size_t
                 // always need to keep the last value
                 break;
             }
-            if (rule->rule_id == RULE_or_test) {
+            if (rule_id == RULE_or_test) {
                 if (mp_parse_node_is_const_true(pn)) {
                     //
                     break;
@@ -487,7 +586,7 @@ STATIC bool fold_logical_constants(parser_t *parser, const rule_t *rule, size_t
         // we did a complete folding if there's only 1 arg left
         return *num_args == 1;
 
-    } else if (rule->rule_id == RULE_not_test_2) {
+    } else if (rule_id == RULE_not_test_2) {
         // folding for unary logical op: not
         mp_parse_node_t pn = peek_result(parser, 0);
         if (mp_parse_node_is_const_false(pn)) {
@@ -505,23 +604,23 @@ STATIC bool fold_logical_constants(parser_t *parser, const rule_t *rule, size_t
     return false;
 }
 
-STATIC bool fold_constants(parser_t *parser, const rule_t *rule, size_t num_args) {
+STATIC bool fold_constants(parser_t *parser, uint8_t rule_id, size_t num_args) {
     // this code does folding of arbitrary integer expressions, eg 1 + 2 * 3 + 4
     // it does not do partial folding, eg 1 + 2 + x -> 3 + x
 
     mp_obj_t arg0;
-    if (rule->rule_id == RULE_expr
-        || rule->rule_id == RULE_xor_expr
-        || rule->rule_id == RULE_and_expr) {
+    if (rule_id == RULE_expr
+        || rule_id == RULE_xor_expr
+        || rule_id == RULE_and_expr) {
         // folding for binary ops: | ^ &
         mp_parse_node_t pn = peek_result(parser, num_args - 1);
         if (!mp_parse_node_get_int_maybe(pn, &arg0)) {
             return false;
         }
         mp_binary_op_t op;
-        if (rule->rule_id == RULE_expr) {
+        if (rule_id == RULE_expr) {
             op = MP_BINARY_OP_OR;
-        } else if (rule->rule_id == RULE_xor_expr) {
+        } else if (rule_id == RULE_xor_expr) {
             op = MP_BINARY_OP_XOR;
         } else {
             op = MP_BINARY_OP_AND;
@@ -534,9 +633,9 @@ STATIC bool fold_constants(parser_t *parser, const rule_t *rule, size_t num_args
             }
             arg0 = mp_binary_op(op, arg0, arg1);
         }
-    } else if (rule->rule_id == RULE_shift_expr
-        || rule->rule_id == RULE_arith_expr
-        || rule->rule_id == RULE_term) {
+    } else if (rule_id == RULE_shift_expr
+        || rule_id == RULE_arith_expr
+        || rule_id == RULE_term) {
         // folding for binary ops: << >> + - * / % //
         mp_parse_node_t pn = peek_result(parser, num_args - 1);
         if (!mp_parse_node_get_int_maybe(pn, &arg0)) {
@@ -580,7 +679,7 @@ STATIC bool fold_constants(parser_t *parser, const rule_t *rule, size_t num_args
             }
             arg0 = mp_binary_op(op, arg0, arg1);
         }
-    } else if (rule->rule_id == RULE_factor_2) {
+    } else if (rule_id == RULE_factor_2) {
         // folding for unary ops: + - ~
         mp_parse_node_t pn = peek_result(parser, 0);
         if (!mp_parse_node_get_int_maybe(pn, &arg0)) {
@@ -599,7 +698,7 @@ STATIC bool fold_constants(parser_t *parser, const rule_t *rule, size_t num_args
         arg0 = mp_unary_op(op, arg0);
 
     #if MICROPY_COMP_CONST
-    } else if (rule->rule_id == RULE_expr_stmt) {
+    } else if (rule_id == RULE_expr_stmt) {
         mp_parse_node_t pn1 = peek_result(parser, 0);
         if (!MP_PARSE_NODE_IS_NULL(pn1)
             && !(MP_PARSE_NODE_IS_STRUCT_KIND(pn1, RULE_expr_stmt_augassign)
@@ -638,7 +737,7 @@ STATIC bool fold_constants(parser_t *parser, const rule_t *rule, size_t num_args
                 if (qstr_str(id)[0] == '_') {
                     pop_result(parser); // pop const(value)
                     pop_result(parser); // pop id
-                    push_result_rule(parser, 0, rules[RULE_pass_stmt], 0); // replace with "pass"
+                    push_result_rule(parser, 0, RULE_pass_stmt, 0); // replace with "pass"
                     return true;
                 }
 
@@ -654,7 +753,7 @@ STATIC bool fold_constants(parser_t *parser, const rule_t *rule, size_t num_args
     #endif
 
     #if MICROPY_COMP_MODULE_CONST
-    } else if (rule->rule_id == RULE_atom_expr_normal) {
+    } else if (rule_id == RULE_atom_expr_normal) {
         mp_parse_node_t pn0 = peek_result(parser, 1);
         mp_parse_node_t pn1 = peek_result(parser, 0);
         if (!(MP_PARSE_NODE_IS_ID(pn0)
@@ -689,7 +788,7 @@ STATIC bool fold_constants(parser_t *parser, const rule_t *rule, size_t num_args
         pop_result(parser);
     }
     if (MP_OBJ_IS_SMALL_INT(arg0)) {
-        push_result_node(parser, mp_parse_node_new_small_int(MP_OBJ_SMALL_INT_VALUE(arg0)));
+        push_result_node(parser, mp_parse_node_new_small_int_checked(parser, arg0));
     } else {
         // TODO reuse memory for parse node struct?
         push_result_node(parser, make_node_const_object(parser, 0, arg0));
@@ -699,9 +798,9 @@ STATIC bool fold_constants(parser_t *parser, const rule_t *rule, size_t num_args
 }
 #endif
 
-STATIC void push_result_rule(parser_t *parser, size_t src_line, const rule_t *rule, size_t num_args) {
+STATIC void push_result_rule(parser_t *parser, size_t src_line, uint8_t rule_id, size_t num_args) {
     // optimise away parenthesis around an expression if possible
-    if (rule->rule_id == RULE_atom_paren) {
+    if (rule_id == RULE_atom_paren) {
         // there should be just 1 arg for this rule
         mp_parse_node_t pn = peek_result(parser, 0);
         if (MP_PARSE_NODE_IS_NULL(pn)) {
@@ -715,11 +814,11 @@ STATIC void push_result_rule(parser_t *parser, size_t src_line, const rule_t *ru
     }
 
     #if MICROPY_COMP_CONST_FOLDING
-    if (fold_logical_constants(parser, rule, &num_args)) {
+    if (fold_logical_constants(parser, rule_id, &num_args)) {
         // we folded this rule so return straight away
         return;
     }
-    if (fold_constants(parser, rule, num_args)) {
+    if (fold_constants(parser, rule_id, num_args)) {
         // we folded this rule so return straight away
         return;
     }
@@ -727,7 +826,7 @@ STATIC void push_result_rule(parser_t *parser, size_t src_line, const rule_t *ru
 
     mp_parse_node_struct_t *pn = parser_alloc(parser, sizeof(mp_parse_node_struct_t) + sizeof(mp_parse_node_t) * num_args);
     pn->source_line = src_line;
-    pn->kind_num_nodes = (rule->rule_id & 0xff) | (num_args << 8);
+    pn->kind_num_nodes = (rule_id & 0xff) | (num_args << 8);
     for (size_t i = num_args; i > 0; i--) {
         pn->nodes[i - 1] = pop_result(parser);
     }
@@ -783,14 +882,11 @@ mp_parse_tree_t mp_parse(mp_lexer_t *lex, mp_parse_input_kind_t input_kind) {
         case MP_PARSE_EVAL_INPUT: top_level_rule = RULE_eval_input; break;
         default: top_level_rule = RULE_file_input;
     }
-    push_rule(&parser, lex->tok_line, rules[top_level_rule], 0);
+    push_rule(&parser, lex->tok_line, top_level_rule, 0);
 
     // parse!
 
-    size_t n, i; // state for the current rule
-    size_t rule_src_line; // source line for the first token matched by the current rule
     bool backtrack = false;
-    const rule_t *rule = NULL;
 
     for (;;) {
         next_rule:
@@ -798,19 +894,24 @@ mp_parse_tree_t mp_parse(mp_lexer_t *lex, mp_parse_input_kind_t input_kind) {
             break;
         }
 
-        pop_rule(&parser, &rule, &i, &rule_src_line);
-        n = rule->act & RULE_ACT_ARG_MASK;
+        // Pop the next rule to process it
+        size_t i; // state for the current rule
+        size_t rule_src_line; // source line for the first token matched by the current rule
+        uint8_t rule_id = pop_rule(&parser, &i, &rule_src_line);
+        uint8_t rule_act = rule_act_table[rule_id];
+        const uint16_t *rule_arg = get_rule_arg(rule_id);
+        size_t n = rule_act & RULE_ACT_ARG_MASK;
 
-        /*
+        #if 0
         // debugging
-        printf("depth=%d ", parser.rule_stack_top);
+        printf("depth=" UINT_FMT " ", parser.rule_stack_top);
         for (int j = 0; j < parser.rule_stack_top; ++j) {
             printf(" ");
         }
-        printf("%s n=%d i=%d bt=%d\n", rule->rule_name, n, i, backtrack);
-        */
+        printf("%s n=" UINT_FMT " i=" UINT_FMT " bt=%d\n", rule_name_table[rule_id], n, i, backtrack);
+        #endif
 
-        switch (rule->act & RULE_ACT_KIND_MASK) {
+        switch (rule_act & RULE_ACT_KIND_MASK) {
             case RULE_ACT_OR:
                 if (i > 0 && !backtrack) {
                     goto next_rule;
@@ -818,19 +919,19 @@ mp_parse_tree_t mp_parse(mp_lexer_t *lex, mp_parse_input_kind_t input_kind) {
                     backtrack = false;
                 }
                 for (; i < n; ++i) {
-                    uint16_t kind = rule->arg[i] & RULE_ARG_KIND_MASK;
+                    uint16_t kind = rule_arg[i] & RULE_ARG_KIND_MASK;
                     if (kind == RULE_ARG_TOK) {
-                        if (lex->tok_kind == (rule->arg[i] & RULE_ARG_ARG_MASK)) {
-                            push_result_token(&parser, rule);
+                        if (lex->tok_kind == (rule_arg[i] & RULE_ARG_ARG_MASK)) {
+                            push_result_token(&parser, rule_id);
                             mp_lexer_to_next(lex);
                             goto next_rule;
                         }
                     } else {
                         assert(kind == RULE_ARG_RULE);
                         if (i + 1 < n) {
-                            push_rule(&parser, rule_src_line, rule, i + 1); // save this or-rule
+                            push_rule(&parser, rule_src_line, rule_id, i + 1); // save this or-rule
                         }
-                        push_rule_from_arg(&parser, rule->arg[i]); // push child of or-rule
+                        push_rule_from_arg(&parser, rule_arg[i]); // push child of or-rule
                         goto next_rule;
                     }
                 }
@@ -842,7 +943,7 @@ mp_parse_tree_t mp_parse(mp_lexer_t *lex, mp_parse_input_kind_t input_kind) {
                 // failed, backtrack if we can, else syntax error
                 if (backtrack) {
                     assert(i > 0);
-                    if ((rule->arg[i - 1] & RULE_ARG_KIND_MASK) == RULE_ARG_OPT_RULE) {
+                    if ((rule_arg[i - 1] & RULE_ARG_KIND_MASK) == RULE_ARG_OPT_RULE) {
                         // an optional rule that failed, so continue with next arg
                         push_result_node(&parser, MP_PARSE_NODE_NULL);
                         backtrack = false;
@@ -859,13 +960,13 @@ mp_parse_tree_t mp_parse(mp_lexer_t *lex, mp_parse_input_kind_t input_kind) {
 
                 // progress through the rule
                 for (; i < n; ++i) {
-                    if ((rule->arg[i] & RULE_ARG_KIND_MASK) == RULE_ARG_TOK) {
+                    if ((rule_arg[i] & RULE_ARG_KIND_MASK) == RULE_ARG_TOK) {
                         // need to match a token
-                        mp_token_kind_t tok_kind = rule->arg[i] & RULE_ARG_ARG_MASK;
+                        mp_token_kind_t tok_kind = rule_arg[i] & RULE_ARG_ARG_MASK;
                         if (lex->tok_kind == tok_kind) {
                             // matched token
                             if (tok_kind == MP_TOKEN_NAME) {
-                                push_result_token(&parser, rule);
+                                push_result_token(&parser, rule_id);
                             }
                             mp_lexer_to_next(lex);
                         } else {
@@ -880,8 +981,8 @@ mp_parse_tree_t mp_parse(mp_lexer_t *lex, mp_parse_input_kind_t input_kind) {
                             }
                         }
                     } else {
-                        push_rule(&parser, rule_src_line, rule, i + 1); // save this and-rule
-                        push_rule_from_arg(&parser, rule->arg[i]); // push child of and-rule
+                        push_rule(&parser, rule_src_line, rule_id, i + 1); // save this and-rule
+                        push_rule_from_arg(&parser, rule_arg[i]); // push child of and-rule
                         goto next_rule;
                     }
                 }
@@ -892,7 +993,7 @@ mp_parse_tree_t mp_parse(mp_lexer_t *lex, mp_parse_input_kind_t input_kind) {
 
                 #if !MICROPY_ENABLE_DOC_STRING
                 // this code discards lonely statements, such as doc strings
-                if (input_kind != MP_PARSE_SINGLE_INPUT && rule->rule_id == RULE_expr_stmt && peek_result(&parser, 0) == MP_PARSE_NODE_NULL) {
+                if (input_kind != MP_PARSE_SINGLE_INPUT && rule_id == RULE_expr_stmt && peek_result(&parser, 0) == MP_PARSE_NODE_NULL) {
                     mp_parse_node_t p = peek_result(&parser, 1);
                     if ((MP_PARSE_NODE_IS_LEAF(p) && !MP_PARSE_NODE_IS_ID(p))
                         || MP_PARSE_NODE_IS_STRUCT_KIND(p, RULE_const_object)) {
@@ -901,7 +1002,7 @@ mp_parse_tree_t mp_parse(mp_lexer_t *lex, mp_parse_input_kind_t input_kind) {
                         // Pushing the "pass" rule here will overwrite any RULE_const_object
                         // entry that was on the result stack, allowing the GC to reclaim
                         // the memory from the const object when needed.
-                        push_result_rule(&parser, rule_src_line, rules[RULE_pass_stmt], 0);
+                        push_result_rule(&parser, rule_src_line, RULE_pass_stmt, 0);
                         break;
                     }
                 }
@@ -912,8 +1013,8 @@ mp_parse_tree_t mp_parse(mp_lexer_t *lex, mp_parse_input_kind_t input_kind) {
                 size_t num_not_nil = 0;
                 for (size_t x = n; x > 0;) {
                     --x;
-                    if ((rule->arg[x] & RULE_ARG_KIND_MASK) == RULE_ARG_TOK) {
-                        mp_token_kind_t tok_kind = rule->arg[x] & RULE_ARG_ARG_MASK;
+                    if ((rule_arg[x] & RULE_ARG_KIND_MASK) == RULE_ARG_TOK) {
+                        mp_token_kind_t tok_kind = rule_arg[x] & RULE_ARG_ARG_MASK;
                         if (tok_kind == MP_TOKEN_NAME) {
                             // only tokens which were names are pushed to stack
                             i += 1;
@@ -928,7 +1029,7 @@ mp_parse_tree_t mp_parse(mp_lexer_t *lex, mp_parse_input_kind_t input_kind) {
                     }
                 }
 
-                if (num_not_nil == 1 && (rule->act & RULE_ACT_ALLOW_IDENT)) {
+                if (num_not_nil == 1 && (rule_act & RULE_ACT_ALLOW_IDENT)) {
                     // this rule has only 1 argument and should not be emitted
                     mp_parse_node_t pn = MP_PARSE_NODE_NULL;
                     for (size_t x = 0; x < i; ++x) {
@@ -941,19 +1042,19 @@ mp_parse_tree_t mp_parse(mp_lexer_t *lex, mp_parse_input_kind_t input_kind) {
                 } else {
                     // this rule must be emitted
 
-                    if (rule->act & RULE_ACT_ADD_BLANK) {
+                    if (rule_act & RULE_ACT_ADD_BLANK) {
                         // and add an extra blank node at the end (used by the compiler to store data)
                         push_result_node(&parser, MP_PARSE_NODE_NULL);
                         i += 1;
                     }
 
-                    push_result_rule(&parser, rule_src_line, rule, i);
+                    push_result_rule(&parser, rule_src_line, rule_id, i);
                 }
                 break;
             }
 
             default: {
-                assert((rule->act & RULE_ACT_KIND_MASK) == RULE_ACT_LIST);
+                assert((rule_act & RULE_ACT_KIND_MASK) == RULE_ACT_LIST);
 
                 // n=2 is: item item*
                 // n=1 is: item (sep item)*
@@ -991,13 +1092,13 @@ mp_parse_tree_t mp_parse(mp_lexer_t *lex, mp_parse_input_kind_t input_kind) {
                     }
                 } else {
                     for (;;) {
-                        size_t arg = rule->arg[i & 1 & n];
+                        size_t arg = rule_arg[i & 1 & n];
                         if ((arg & RULE_ARG_KIND_MASK) == RULE_ARG_TOK) {
                             if (lex->tok_kind == (arg & RULE_ARG_ARG_MASK)) {
                                 if (i & 1 & n) {
                                     // separators which are tokens are not pushed to result stack
                                 } else {
-                                    push_result_token(&parser, rule);
+                                    push_result_token(&parser, rule_id);
                                 }
                                 mp_lexer_to_next(lex);
                                 // got element of list, so continue parsing list
@@ -1010,7 +1111,7 @@ mp_parse_tree_t mp_parse(mp_lexer_t *lex, mp_parse_input_kind_t input_kind) {
                             }
                         } else {
                             assert((arg & RULE_ARG_KIND_MASK) == RULE_ARG_RULE);
-                            push_rule(&parser, rule_src_line, rule, i + 1); // save this list-rule
+                            push_rule(&parser, rule_src_line, rule_id, i + 1); // save this list-rule
                             push_rule_from_arg(&parser, arg); // push child of list-rule
                             goto next_rule;
                         }
@@ -1020,7 +1121,7 @@ mp_parse_tree_t mp_parse(mp_lexer_t *lex, mp_parse_input_kind_t input_kind) {
 
                 // compute number of elements in list, result in i
                 i -= 1;
-                if ((n & 1) && (rule->arg[1] & RULE_ARG_KIND_MASK) == RULE_ARG_TOK) {
+                if ((n & 1) && (rule_arg[1] & RULE_ARG_KIND_MASK) == RULE_ARG_TOK) {
                     // don't count separators when they are tokens
                     i = (i + 1) / 2;
                 }
@@ -1029,12 +1130,12 @@ mp_parse_tree_t mp_parse(mp_lexer_t *lex, mp_parse_input_kind_t input_kind) {
                     // list matched single item
                     if (had_trailing_sep) {
                         // if there was a trailing separator, make a list of a single item
-                        push_result_rule(&parser, rule_src_line, rule, i);
+                        push_result_rule(&parser, rule_src_line, rule_id, i);
                     } else {
                         // just leave single item on stack (ie don't wrap in a list)
                     }
                 } else {
-                    push_result_rule(&parser, rule_src_line, rule, i);
+                    push_result_rule(&parser, rule_src_line, rule_id, i);
                 }
                 break;
             }
diff --git a/py/parsenum.c b/py/parsenum.c
index bacf4f442..e3644b171 100644
--- a/py/parsenum.c
+++ b/py/parsenum.c
@@ -83,6 +83,8 @@ mp_obj_t mp_parse_num_integer(const char *restrict str_, size_t len, int base, m
         mp_uint_t dig = *str;
         if ('0' <= dig && dig <= '9') {
             dig -= '0';
+        } else if (dig == '_') {
+            continue;
         } else {
             dig |= 0x20; // make digit lower-case
             if ('a' <= dig && dig <= 'z') {
@@ -170,6 +172,19 @@ typedef enum {
 
 mp_obj_t mp_parse_num_decimal(const char *str, size_t len, bool allow_imag, bool force_complex, mp_lexer_t *lex) {
 #if MICROPY_PY_BUILTINS_FLOAT
+
+// DEC_VAL_MAX only needs to be rough and is used to retain precision while not overflowing
+// SMALL_NORMAL_VAL is the smallest power of 10 that is still a normal float
+#if MICROPY_FLOAT_IMPL == MICROPY_FLOAT_IMPL_FLOAT
+#define DEC_VAL_MAX 1e20F
+#define SMALL_NORMAL_VAL (1e-37F)
+#define SMALL_NORMAL_EXP (-37)
+#elif MICROPY_FLOAT_IMPL == MICROPY_FLOAT_IMPL_DOUBLE
+#define DEC_VAL_MAX 1e200
+#define SMALL_NORMAL_VAL (1e-307)
+#define SMALL_NORMAL_EXP (-307)
+#endif
+
     const char *top = str + len;
     mp_float_t dec_val = 0;
     bool dec_neg = false;
@@ -214,20 +229,32 @@ mp_obj_t mp_parse_num_decimal(const char *str, size_t len, bool allow_imag, bool
         // string should be a decimal number
         parse_dec_in_t in = PARSE_DEC_IN_INTG;
         bool exp_neg = false;
-        mp_float_t frac_mult = 0.1;
-        mp_int_t exp_val = 0;
+        int exp_val = 0;
+        int exp_extra = 0;
         while (str < top) {
-            mp_uint_t dig = *str++;
+            unsigned int dig = *str++;
             if ('0' <= dig && dig <= '9') {
                 dig -= '0';
                 if (in == PARSE_DEC_IN_EXP) {
-                    exp_val = 10 * exp_val + dig;
+                    // don't overflow exp_val when adding next digit, instead just truncate
+                    // it and the resulting float will still be correct, either inf or 0.0
+                    // (use INT_MAX/2 to allow adding exp_extra at the end without overflow)
+                    if (exp_val < (INT_MAX / 2 - 9) / 10) {
+                        exp_val = 10 * exp_val + dig;
+                    }
                 } else {
-                    if (in == PARSE_DEC_IN_FRAC) {
-                        dec_val += dig * frac_mult;
-                        frac_mult *= MICROPY_FLOAT_CONST(0.1);
-                    } else {
+                    if (dec_val < DEC_VAL_MAX) {
+                        // dec_val won't overflow so keep accumulating
                         dec_val = 10 * dec_val + dig;
+                        if (in == PARSE_DEC_IN_FRAC) {
+                            --exp_extra;
+                        }
+                    } else {
+                        // dec_val might overflow and we anyway can't represent more digits
+                        // of precision, so ignore the digit and just adjust the exponent
+                        if (in == PARSE_DEC_IN_INTG) {
+                            ++exp_extra;
+                        }
                     }
                 }
             } else if (in == PARSE_DEC_IN_INTG && dig == '.') {
@@ -248,6 +275,8 @@ mp_obj_t mp_parse_num_decimal(const char *str, size_t len, bool allow_imag, bool
             } else if (allow_imag && (dig | 0x20) == 'j') {
                 imag = true;
                 break;
+            } else if (dig == '_') {
+                continue;
             } else {
                 // unknown character
                 str--;
@@ -260,7 +289,12 @@ mp_obj_t mp_parse_num_decimal(const char *str, size_t len, bool allow_imag, bool
             exp_val = -exp_val;
         }
 
-        // apply the exponent
+        // apply the exponent, making sure it's not a subnormal value
+        exp_val += exp_extra;
+        if (exp_val < SMALL_NORMAL_EXP) {
+            exp_val -= SMALL_NORMAL_EXP;
+            dec_val *= SMALL_NORMAL_VAL;
+        }
         dec_val *= MICROPY_FLOAT_C_FUN(pow)(10, exp_val);
     }
 
@@ -289,11 +323,13 @@ mp_obj_t mp_parse_num_decimal(const char *str, size_t len, bool allow_imag, bool
         return mp_obj_new_complex(0, dec_val);
     } else if (force_complex) {
         return mp_obj_new_complex(dec_val, 0);
+    }
 #else
     if (imag || force_complex) {
         raise_exc(mp_obj_new_exception_msg(&mp_type_ValueError, "complex values not supported"), lex);
+    }
 #endif
-    } else {
+    else {
         return mp_obj_new_float(dec_val);
     }
 
diff --git a/py/persistentcode.c b/py/persistentcode.c
index ba126a3fb..290797a7c 100644
--- a/py/persistentcode.c
+++ b/py/persistentcode.c
@@ -199,7 +199,11 @@ STATIC mp_raw_code_t *load_raw_code(mp_reader_t *reader) {
 
     // create raw_code and return it
     mp_raw_code_t *rc = mp_emit_glue_new_raw_code();
-    mp_emit_glue_assign_bytecode(rc, bytecode, bc_len, const_table,
+    mp_emit_glue_assign_bytecode(rc, bytecode,
+        #if MICROPY_PERSISTENT_CODE_SAVE || MICROPY_DEBUG_PRINTERS
+        bc_len,
+        #endif
+        const_table,
         #if MICROPY_PERSISTENT_CODE_SAVE
         n_obj, n_raw_code,
         #endif
diff --git a/py/py.mk b/py/py.mk
index e934c3a83..cad8b53ec 100644
--- a/py/py.mk
+++ b/py/py.mk
@@ -13,6 +13,9 @@ ifneq ($(QSTR_AUTOGEN_DISABLE),1)
 QSTR_DEFS_COLLECTED = $(HEADER_BUILD)/qstrdefs.collected.h
 endif
 
+# Any files listed by this variable will cause a full regeneration of qstrs
+QSTR_GLOBAL_DEPENDENCIES += $(PY_SRC)/mpconfig.h mpconfigport.h
+
 # some code is performance bottleneck and compiled with other optimization options
 CSUPEROPT = -O3
 
@@ -101,8 +104,9 @@ $(BUILD)/extmod/modbtree.o: CFLAGS += $(BTREE_DEFS)
 endif
 
 # py object files
-PY_O_BASENAME = \
+PY_CORE_O_BASENAME = $(addprefix py/,\
 	mpstate.o \
+	nlr.o \
 	nlrx86.o \
 	nlrx64.o \
 	nlrthumb.o \
@@ -111,6 +115,7 @@ PY_O_BASENAME = \
 	malloc.o \
 	gc.o \
 	gc_long_lived.o \
+	pystack.o \
 	qstr.o \
 	vstr.o \
 	mpprint.o \
@@ -157,6 +162,7 @@ PY_O_BASENAME = \
 	objcell.o \
 	objclosure.o \
 	objcomplex.o \
+	objdeque.o \
 	objdict.o \
 	objenumerate.o \
 	objexcept.o \
@@ -213,41 +219,49 @@ PY_O_BASENAME = \
 	repl.o \
 	smallint.o \
 	frozenmod.o \
-	../extmod/moductypes.o \
-	../extmod/modujson.o \
-	../extmod/modure.o \
-	../extmod/moduzlib.o \
-	../extmod/moduheapq.o \
-	../extmod/modutimeq.o \
-	../extmod/moduhashlib.o \
-	../extmod/modubinascii.o \
-	../extmod/virtpin.o \
-	../extmod/machine_mem.o \
-	../extmod/machine_pinbase.o \
-	../extmod/machine_signal.o \
-	../extmod/machine_pulse.o \
-	../extmod/machine_i2c.o \
-	../extmod/machine_spi.o \
-	../extmod/modussl_axtls.o \
-	../extmod/modussl_mbedtls.o \
-	../extmod/modurandom.o \
-	../extmod/moduselect.o \
-	../extmod/modwebsocket.o \
-	../extmod/modwebrepl.o \
-	../extmod/modframebuf.o \
-	../extmod/vfs.o \
-	../extmod/vfs_reader.o \
-	../extmod/vfs_fat.o \
-	../extmod/vfs_fat_diskio.o \
-	../extmod/vfs_fat_file.o \
-	../extmod/vfs_fat_misc.o \
-	../extmod/utime_mphal.o \
-	../extmod/uos_dupterm.o \
-	../lib/embed/abort_.o \
-	../lib/utils/printf.o \
+	)
+
+PY_EXTMOD_O_BASENAME = \
+	extmod/moductypes.o \
+	extmod/modujson.o \
+	extmod/modure.o \
+	extmod/moduzlib.o \
+	extmod/moduheapq.o \
+	extmod/modutimeq.o \
+	extmod/moduhashlib.o \
+	extmod/modubinascii.o \
+	extmod/virtpin.o \
+	extmod/machine_mem.o \
+	extmod/machine_pinbase.o \
+	extmod/machine_signal.o \
+	extmod/machine_pulse.o \
+	extmod/machine_i2c.o \
+	extmod/machine_spi.o \
+	extmod/modussl_axtls.o \
+	extmod/modussl_mbedtls.o \
+	extmod/modurandom.o \
+	extmod/moduselect.o \
+	extmod/modwebsocket.o \
+	extmod/modwebrepl.o \
+	extmod/modframebuf.o \
+	extmod/vfs.o \
+	extmod/vfs_reader.o \
+	extmod/vfs_posix.o \
+	extmod/vfs_posix_file.o \
+	extmod/vfs_fat.o \
+	extmod/vfs_fat_diskio.o \
+	extmod/vfs_fat_file.o \
+	extmod/utime_mphal.o \
+	extmod/uos_dupterm.o \
+	lib/embed/abort_.o \
+	lib/utils/printf.o \
 
 # prepend the build destination prefix to the py object files
-PY_O = $(addprefix $(PY_BUILD)/, $(PY_O_BASENAME))
+PY_CORE_O = $(addprefix $(BUILD)/, $(PY_CORE_O_BASENAME))
+PY_EXTMOD_O = $(addprefix $(BUILD)/, $(PY_EXTMOD_O_BASENAME))
+
+# this is a convenience variable for ports that want core, extmod and frozen code
+PY_O = $(PY_CORE_O) $(PY_EXTMOD_O)
 
 # object file for frozen files
 ifneq ($(FROZEN_DIR),)
@@ -263,8 +277,8 @@ PY_O += $(BUILD)/frozen_mpy.o
 endif
 
 # Sources that may contain qstrings
-SRC_QSTR_IGNORE = nlr% emitnx86% emitnx64% emitnthumb% emitnarm% emitnxtensa%
-SRC_QSTR = $(SRC_MOD) $(addprefix py/,$(filter-out $(SRC_QSTR_IGNORE),$(PY_O_BASENAME:.o=.c)) emitnative.c)
+SRC_QSTR_IGNORE = py/nlr%
+SRC_QSTR = $(SRC_MOD) $(filter-out $(SRC_QSTR_IGNORE),$(PY_CORE_O_BASENAME:.o=.c)) $(PY_EXTMOD_O_BASENAME:.o=.c)
 
 # Anything that depends on FORCE will be considered out-of-date
 FORCE:
@@ -291,28 +305,6 @@ $(HEADER_BUILD)/qstrdefs.generated.h: $(PY_QSTR_DEFS) $(QSTR_DEFS) $(QSTR_DEFS_C
 # that the function preludes are of a minimal and predictable form.
 $(PY_BUILD)/nlr%.o: CFLAGS += -Os
 
-# emitters
-
-$(PY_BUILD)/emitnx64.o: CFLAGS += -DN_X64
-$(PY_BUILD)/emitnx64.o: py/emitnative.c
-	$(call compile_c)
-
-$(PY_BUILD)/emitnx86.o: CFLAGS += -DN_X86
-$(PY_BUILD)/emitnx86.o: py/emitnative.c
-	$(call compile_c)
-
-$(PY_BUILD)/emitnthumb.o: CFLAGS += -DN_THUMB
-$(PY_BUILD)/emitnthumb.o: py/emitnative.c
-	$(call compile_c)
-
-$(PY_BUILD)/emitnarm.o: CFLAGS += -DN_ARM
-$(PY_BUILD)/emitnarm.o: py/emitnative.c
-	$(call compile_c)
-
-$(PY_BUILD)/emitnxtensa.o: CFLAGS += -DN_XTENSA
-$(PY_BUILD)/emitnxtensa.o: py/emitnative.c
-	$(call compile_c)
-
 # optimising gc for speed; 5ms down to 4ms on pybv2
 $(PY_BUILD)/gc.o: CFLAGS += $(CSUPEROPT)
 
diff --git a/py/pystack.c b/py/pystack.c
new file mode 100644
index 000000000..552e59d53
--- /dev/null
+++ b/py/pystack.c
@@ -0,0 +1,57 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2017 Damien P. George
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include <stdio.h>
+
+#include "py/runtime.h"
+
+#if MICROPY_ENABLE_PYSTACK
+
+void mp_pystack_init(void *start, void *end) {
+    MP_STATE_THREAD(pystack_start) = start;
+    MP_STATE_THREAD(pystack_end) = end;
+    MP_STATE_THREAD(pystack_cur) = start;
+}
+
+void *mp_pystack_alloc(size_t n_bytes) {
+    n_bytes = (n_bytes + (MICROPY_PYSTACK_ALIGN - 1)) & ~(MICROPY_PYSTACK_ALIGN - 1);
+    #if MP_PYSTACK_DEBUG
+    n_bytes += MICROPY_PYSTACK_ALIGN;
+    #endif
+    if (MP_STATE_THREAD(pystack_cur) + n_bytes > MP_STATE_THREAD(pystack_end)) {
+        // out of memory in the pystack
+        nlr_raise(mp_obj_new_exception_arg1(&mp_type_RuntimeError,
+            MP_OBJ_NEW_QSTR(MP_QSTR_pystack_space_exhausted)));
+    }
+    void *ptr = MP_STATE_THREAD(pystack_cur);
+    MP_STATE_THREAD(pystack_cur) += n_bytes;
+    #if MP_PYSTACK_DEBUG
+    *(size_t*)(MP_STATE_THREAD(pystack_cur) - MICROPY_PYSTACK_ALIGN) = n_bytes;
+    #endif
+    return ptr;
+}
+
+#endif
diff --git a/py/pystack.h b/py/pystack.h
new file mode 100644
index 000000000..82ac3743d
--- /dev/null
+++ b/py/pystack.h
@@ -0,0 +1,123 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2017 Damien P. George
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+#ifndef MICROPY_INCLUDED_PY_PYSTACK_H
+#define MICROPY_INCLUDED_PY_PYSTACK_H
+
+#include "py/mpstate.h"
+
+// Enable this debugging option to check that the amount of memory freed is
+// consistent with amounts that were previously allocated.
+#define MP_PYSTACK_DEBUG (0)
+
+#if MICROPY_ENABLE_PYSTACK
+
+void mp_pystack_init(void *start, void *end);
+void *mp_pystack_alloc(size_t n_bytes);
+
+// This function can free multiple continuous blocks at once: just pass the
+// pointer to the block that was allocated first and it and all subsequently
+// allocated blocks will be freed.
+static inline void mp_pystack_free(void *ptr) {
+    assert((uint8_t*)ptr >= MP_STATE_THREAD(pystack_start));
+    assert((uint8_t*)ptr <= MP_STATE_THREAD(pystack_cur));
+    #if MP_PYSTACK_DEBUG
+    size_t n_bytes_to_free = MP_STATE_THREAD(pystack_cur) - (uint8_t*)ptr;
+    size_t n_bytes = *(size_t*)(MP_STATE_THREAD(pystack_cur) - MICROPY_PYSTACK_ALIGN);
+    while (n_bytes < n_bytes_to_free) {
+        n_bytes += *(size_t*)(MP_STATE_THREAD(pystack_cur) - n_bytes - MICROPY_PYSTACK_ALIGN);
+    }
+    if (n_bytes != n_bytes_to_free) {
+        mp_printf(&mp_plat_print, "mp_pystack_free() failed: %u != %u\n", (uint)n_bytes_to_free,
+            (uint)*(size_t*)(MP_STATE_THREAD(pystack_cur) - MICROPY_PYSTACK_ALIGN));
+        assert(0);
+    }
+    #endif
+    MP_STATE_THREAD(pystack_cur) = (uint8_t*)ptr;
+}
+
+static inline void mp_pystack_realloc(void *ptr, size_t n_bytes) {
+    mp_pystack_free(ptr);
+    mp_pystack_alloc(n_bytes);
+}
+
+static inline size_t mp_pystack_usage(void) {
+    return MP_STATE_THREAD(pystack_cur) - MP_STATE_THREAD(pystack_start);
+}
+
+static inline size_t mp_pystack_limit(void) {
+    return MP_STATE_THREAD(pystack_end) - MP_STATE_THREAD(pystack_start);
+}
+
+#endif
+
+#if !MICROPY_ENABLE_PYSTACK
+
+#define mp_local_alloc(n_bytes) alloca(n_bytes)
+
+static inline void mp_local_free(void *ptr) {
+    (void)ptr;
+}
+
+static inline void *mp_nonlocal_alloc(size_t n_bytes) {
+    return m_new(uint8_t, n_bytes);
+}
+
+static inline void *mp_nonlocal_realloc(void *ptr, size_t old_n_bytes, size_t new_n_bytes) {
+    return m_renew(uint8_t, ptr, old_n_bytes, new_n_bytes);
+}
+
+static inline void mp_nonlocal_free(void *ptr, size_t n_bytes) {
+    m_del(uint8_t, ptr, n_bytes);
+}
+
+#else
+
+static inline void *mp_local_alloc(size_t n_bytes) {
+    return mp_pystack_alloc(n_bytes);
+}
+
+static inline void mp_local_free(void *ptr) {
+    mp_pystack_free(ptr);
+}
+
+static inline void *mp_nonlocal_alloc(size_t n_bytes) {
+    return mp_pystack_alloc(n_bytes);
+}
+
+static inline void *mp_nonlocal_realloc(void *ptr, size_t old_n_bytes, size_t new_n_bytes) {
+    (void)old_n_bytes;
+    mp_pystack_realloc(ptr, new_n_bytes);
+    return ptr;
+}
+
+static inline void mp_nonlocal_free(void *ptr, size_t n_bytes) {
+    (void)n_bytes;
+    mp_pystack_free(ptr);
+}
+
+#endif
+
+#endif // MICROPY_INCLUDED_PY_PYSTACK_H
diff --git a/py/qstr.c b/py/qstr.c
index de4dc6240..c68f3dfec 100755
--- a/py/qstr.c
+++ b/py/qstr.c
@@ -128,14 +128,12 @@ void qstr_init(void) {
 
 STATIC const byte *find_qstr(qstr q) {
     // search pool for this qstr
-    for (qstr_pool_t *pool = MP_STATE_VM(last_pool); pool != NULL; pool = pool->prev) {
-        if (q >= pool->total_prev_len) {
-            return pool->qstrs[q - pool->total_prev_len];
-        }
+    // total_prev_len==0 in the final pool, so the loop will always terminate
+    qstr_pool_t *pool = MP_STATE_VM(last_pool);
+    while (q < pool->total_prev_len) {
+        pool = pool->prev;
     }
-
-    // not found
-    return 0;
+    return pool->qstrs[q - pool->total_prev_len];
 }
 
 // qstr_mutex must be taken while in this function
@@ -248,29 +246,6 @@ qstr qstr_from_strn(const char *str, size_t len) {
     return q;
 }
 
-byte *qstr_build_start(size_t len, byte **q_ptr) {
-    assert(len < (1 << (8 * MICROPY_QSTR_BYTES_IN_LEN)));
-    *q_ptr = m_new(byte, MICROPY_QSTR_BYTES_IN_HASH + MICROPY_QSTR_BYTES_IN_LEN + len + 1);
-    Q_SET_LENGTH(*q_ptr, len);
-    return Q_GET_DATA(*q_ptr);
-}
-
-qstr qstr_build_end(byte *q_ptr) {
-    QSTR_ENTER();
-    qstr q = qstr_find_strn((const char*)Q_GET_DATA(q_ptr), Q_GET_LENGTH(q_ptr));
-    if (q == 0) {
-        size_t len = Q_GET_LENGTH(q_ptr);
-        mp_uint_t hash = qstr_compute_hash(Q_GET_DATA(q_ptr), len);
-        Q_SET_HASH(q_ptr, hash);
-        q_ptr[MICROPY_QSTR_BYTES_IN_HASH + MICROPY_QSTR_BYTES_IN_LEN + len] = '\0';
-        q = qstr_add(gc_make_long_lived(q_ptr));
-    } else {
-        m_del(byte, q_ptr, Q_GET_ALLOC(q_ptr));
-    }
-    QSTR_EXIT();
-    return q;
-}
-
 mp_uint_t qstr_hash(qstr q) {
     return Q_GET_HASH(find_qstr(q));
 }
diff --git a/py/qstr.h b/py/qstr.h
index e2bdcc351..f4375ee0e 100644
--- a/py/qstr.h
+++ b/py/qstr.h
@@ -56,6 +56,7 @@ typedef struct _qstr_pool_t {
 } qstr_pool_t;
 
 #define QSTR_FROM_STR_STATIC(s) (qstr_from_strn((s), strlen(s)))
+#define QSTR_TOTAL() (MP_STATE_VM(last_pool)->total_prev_len + MP_STATE_VM(last_pool)->len)
 
 void qstr_init(void);
 
@@ -65,9 +66,6 @@ qstr qstr_find_strn(const char *str, size_t str_len); // returns MP_QSTR_NULL if
 qstr qstr_from_str(const char *str);
 qstr qstr_from_strn(const char *str, size_t len);
 
-byte *qstr_build_start(size_t len, byte **q_ptr);
-qstr qstr_build_end(byte *q_ptr);
-
 mp_uint_t qstr_hash(qstr q);
 const char *qstr_str(qstr q);
 size_t qstr_len(qstr q);
diff --git a/py/qstrdefs.h b/py/qstrdefs.h
index 4ded5be08..a60905812 100644
--- a/py/qstrdefs.h
+++ b/py/qstrdefs.h
@@ -40,6 +40,7 @@ Q(/)
 Q(%#o)
 Q(%#x)
 Q({:#b})
+Q( )
 Q(\n)
 Q(maximum recursion depth exceeded)
 Q(<module>)
@@ -51,3 +52,7 @@ Q(<genexpr>)
 Q(<string>)
 Q(<stdin>)
 Q(utf-8)
+
+#if MICROPY_ENABLE_PYSTACK
+Q(pystack exhausted)
+#endif
diff --git a/py/reader.c b/py/reader.c
index c4d18d53d..80364104b 100644
--- a/py/reader.c
+++ b/py/reader.c
@@ -124,6 +124,8 @@ void mp_reader_new_file_from_fd(mp_reader_t *reader, int fd, bool close_fd) {
     reader->close = mp_reader_posix_close;
 }
 
+#if !MICROPY_VFS_POSIX
+// If MICROPY_VFS_POSIX is defined then this function is provided by the VFS layer
 void mp_reader_new_file(mp_reader_t *reader, const char *filename) {
     int fd = open(filename, O_RDONLY, 0644);
     if (fd < 0) {
@@ -131,5 +133,6 @@ void mp_reader_new_file(mp_reader_t *reader, const char *filename) {
     }
     mp_reader_new_file_from_fd(reader, fd, true);
 }
+#endif
 
 #endif
diff --git a/py/repl.c b/py/repl.c
index 7e8922e19..da0fefb3a 100644
--- a/py/repl.c
+++ b/py/repl.c
@@ -27,6 +27,7 @@
 #include <string.h>
 #include "py/obj.h"
 #include "py/runtime.h"
+#include "py/builtin.h"
 #include "py/repl.h"
 
 #if MICROPY_HELPER_REPL
@@ -105,8 +106,13 @@ bool mp_repl_continue_with_input(const char *input) {
         }
     }
 
-    // continue if unmatched brackets or quotes
-    if (n_paren > 0 || n_brack > 0 || n_brace > 0 || in_quote == Q_3_SINGLE || in_quote == Q_3_DOUBLE) {
+    // continue if unmatched 3-quotes
+    if (in_quote == Q_3_SINGLE || in_quote == Q_3_DOUBLE) {
+        return true;
+    }
+
+    // continue if unmatched brackets, but only if not in a 1-quote
+    if ((n_paren > 0 || n_brack > 0 || n_brace > 0) && in_quote == Q_NONE) {
         return true;
     }
 
@@ -136,8 +142,11 @@ size_t mp_repl_autocomplete(const char *str, size_t len, const mp_print_t *print
         }
     }
 
-    // begin search in locals dict
-    mp_obj_dict_t *dict = mp_locals_get();
+    size_t nqstr = QSTR_TOTAL();
+
+    // begin search in outer global dict which is accessed from __main__
+    mp_obj_t obj = MP_OBJ_FROM_PTR(&mp_module___main__);
+    mp_obj_t dest[2];
 
     for (;;) {
         // get next word in string to complete
@@ -148,43 +157,20 @@ size_t mp_repl_autocomplete(const char *str, size_t len, const mp_print_t *print
         size_t s_len = str - s_start;
 
         if (str < top) {
-            // a complete word, lookup in current dict
-
-            mp_obj_t obj = MP_OBJ_NULL;
-            for (size_t i = 0; i < dict->map.alloc; i++) {
-                if (MP_MAP_SLOT_IS_FILLED(&dict->map, i)) {
-                    size_t d_len;
-                    const char *d_str = mp_obj_str_get_data(dict->map.table[i].key, &d_len);
-                    if (s_len == d_len && strncmp(s_start, d_str, d_len) == 0) {
-                        obj = dict->map.table[i].value;
-                        break;
-                    }
-                }
+            // a complete word, lookup in current object
+            qstr q = qstr_find_strn(s_start, s_len);
+            if (q == MP_QSTR_NULL) {
+                // lookup will fail
+                return 0;
             }
+            mp_load_method_protected(obj, q, dest, true);
+            obj = dest[0]; // attribute, method, or MP_OBJ_NULL if nothing found
 
             if (obj == MP_OBJ_NULL) {
                 // lookup failed
                 return 0;
             }
 
-            // found an object of this name; try to get its dict
-            if (MP_OBJ_IS_TYPE(obj, &mp_type_module)) {
-                dict = mp_obj_module_get_globals(obj);
-            } else {
-                mp_obj_type_t *type;
-                if (MP_OBJ_IS_TYPE(obj, &mp_type_type)) {
-                    type = MP_OBJ_TO_PTR(obj);
-                } else {
-                    type = mp_obj_get_type(obj);
-                }
-                if (type->locals_dict != NULL && type->locals_dict->base.type == &mp_type_dict) {
-                    dict = type->locals_dict;
-                } else {
-                    // obj has no dict
-                    return 0;
-                }
-            }
-
             // skip '.' to move to next word
             ++str;
 
@@ -192,14 +178,15 @@ size_t mp_repl_autocomplete(const char *str, size_t len, const mp_print_t *print
             // end of string, do completion on this partial name
 
             // look for matches
-            int n_found = 0;
             const char *match_str = NULL;
             size_t match_len = 0;
-            for (size_t i = 0; i < dict->map.alloc; i++) {
-                if (MP_MAP_SLOT_IS_FILLED(&dict->map, i)) {
-                    size_t d_len;
-                    const char *d_str = mp_obj_str_get_data(dict->map.table[i].key, &d_len);
-                    if (s_len <= d_len && strncmp(s_start, d_str, s_len) == 0) {
+            qstr q_first = 0, q_last = 0;
+            for (qstr q = MP_QSTR_ + 1; q < nqstr; ++q) {
+                size_t d_len;
+                const char *d_str = (const char*)qstr_data(q, &d_len);
+                if (s_len <= d_len && strncmp(s_start, d_str, s_len) == 0) {
+                    mp_load_method_protected(obj, q, dest, true);
+                    if (dest[0] != MP_OBJ_NULL) {
                         if (match_str == NULL) {
                             match_str = d_str;
                             match_len = d_len;
@@ -213,13 +200,16 @@ size_t mp_repl_autocomplete(const char *str, size_t len, const mp_print_t *print
                                 }
                             }
                         }
-                        ++n_found;
+                        if (q_first == 0) {
+                            q_first = q;
+                        }
+                        q_last = q;
                     }
                 }
             }
 
             // nothing found
-            if (n_found == 0) {
+            if (q_first == 0) {
                 // If there're no better alternatives, and if it's first word
                 // in the line, try to complete "import".
                 if (s_start == org_str) {
@@ -234,7 +224,7 @@ size_t mp_repl_autocomplete(const char *str, size_t len, const mp_print_t *print
             }
 
             // 1 match found, or multiple matches with a common prefix
-            if (n_found == 1 || match_len > s_len) {
+            if (q_first == q_last || match_len > s_len) {
                 *compl_str = match_str + s_len;
                 return match_len - s_len;
             }
@@ -245,11 +235,12 @@ size_t mp_repl_autocomplete(const char *str, size_t len, const mp_print_t *print
             #define MAX_LINE_LEN  (4 * WORD_SLOT_LEN)
 
             int line_len = MAX_LINE_LEN; // force a newline for first word
-            for (size_t i = 0; i < dict->map.alloc; i++) {
-                if (MP_MAP_SLOT_IS_FILLED(&dict->map, i)) {
-                    size_t d_len;
-                    const char *d_str = mp_obj_str_get_data(dict->map.table[i].key, &d_len);
-                    if (s_len <= d_len && strncmp(s_start, d_str, s_len) == 0) {
+            for (qstr q = q_first; q <= q_last; ++q) {
+                size_t d_len;
+                const char *d_str = (const char*)qstr_data(q, &d_len);
+                if (s_len <= d_len && strncmp(s_start, d_str, s_len) == 0) {
+                    mp_load_method_protected(obj, q, dest, true);
+                    if (dest[0] != MP_OBJ_NULL) {
                         int gap = (line_len + WORD_SLOT_LEN - 1) / WORD_SLOT_LEN * WORD_SLOT_LEN - line_len;
                         if (gap < 2) {
                             gap += WORD_SLOT_LEN;
diff --git a/py/runtime.c b/py/runtime.c
index a7ff57a47..a9c0ef1e2 100644
--- a/py/runtime.c
+++ b/py/runtime.c
@@ -95,8 +95,10 @@ void mp_init(void) {
     MICROPY_PORT_INIT_FUNC;
 #endif
 
+    #if MICROPY_ENABLE_COMPILER
     // optimization disabled by default
     MP_STATE_VM(mp_optimise_value) = 0;
+    #endif
 
     // init global module dict
     mp_obj_dict_init(&MP_STATE_VM(mp_loaded_modules_dict), 3);
@@ -118,7 +120,6 @@ void mp_init(void) {
     for (size_t i = 0; i < MICROPY_PY_OS_DUPTERM; ++i) {
         MP_STATE_VM(dupterm_objs[i]) = MP_OBJ_NULL;
     }
-    MP_STATE_VM(dupterm_arr_obj) = MP_OBJ_NULL;
     #endif
 
     #ifdef MICROPY_FSUSERMOUNT
@@ -246,7 +247,7 @@ void mp_delete_global(qstr qst) {
 }
 
 mp_obj_t mp_unary_op(mp_unary_op_t op, mp_obj_t arg) {
-    DEBUG_OP_printf("unary " UINT_FMT " %p\n", op, arg);
+    DEBUG_OP_printf("unary " UINT_FMT " %q %p\n", op, mp_unary_op_method_name[op], arg);
 
     if (op == MP_UNARY_OP_NOT) {
         // "not x" is the negative of whether "x" is true per Python semantics
@@ -307,7 +308,7 @@ mp_obj_t mp_unary_op(mp_unary_op_t op, mp_obj_t arg) {
 }
 
 mp_obj_t mp_binary_op(mp_binary_op_t op, mp_obj_t lhs, mp_obj_t rhs) {
-    DEBUG_OP_printf("binary " UINT_FMT " %p %p\n", op, lhs, rhs);
+    DEBUG_OP_printf("binary " UINT_FMT " %q %p %p\n", op, mp_binary_op_method_name[op], lhs, rhs);
 
     // TODO correctly distinguish inplace operators for mutable objects
     // lookup logic that CPython uses for +=:
@@ -445,7 +446,6 @@ mp_obj_t mp_binary_op(mp_binary_op_t op, mp_obj_t lhs, mp_obj_t rhs) {
                         // use standard precision
                         return MP_OBJ_NEW_SMALL_INT(lhs_val * rhs_val);
                     }
-                    break;
                 }
                 case MP_BINARY_OP_FLOOR_DIVIDE:
                 case MP_BINARY_OP_INPLACE_FLOOR_DIVIDE:
@@ -520,10 +520,10 @@ mp_obj_t mp_binary_op(mp_binary_op_t op, mp_obj_t lhs, mp_obj_t rhs) {
                     return MP_OBJ_FROM_PTR(tuple);
                 }
 
-                case MP_BINARY_OP_LESS: return mp_obj_new_bool(lhs_val < rhs_val); break;
-                case MP_BINARY_OP_MORE: return mp_obj_new_bool(lhs_val > rhs_val); break;
-                case MP_BINARY_OP_LESS_EQUAL: return mp_obj_new_bool(lhs_val <= rhs_val); break;
-                case MP_BINARY_OP_MORE_EQUAL: return mp_obj_new_bool(lhs_val >= rhs_val); break;
+                case MP_BINARY_OP_LESS: return mp_obj_new_bool(lhs_val < rhs_val);
+                case MP_BINARY_OP_MORE: return mp_obj_new_bool(lhs_val > rhs_val);
+                case MP_BINARY_OP_LESS_EQUAL: return mp_obj_new_bool(lhs_val <= rhs_val);
+                case MP_BINARY_OP_MORE_EQUAL: return mp_obj_new_bool(lhs_val >= rhs_val);
 
                 default:
                     goto unsupported_op;
@@ -555,38 +555,12 @@ mp_obj_t mp_binary_op(mp_binary_op_t op, mp_obj_t lhs, mp_obj_t rhs) {
         }
     }
 
-    /* deal with `in`
-     *
-     * NOTE `a in b` is `b.__contains__(a)`, hence why the generic dispatch
-     * needs to go below with swapped arguments
-     */
+    // Convert MP_BINARY_OP_IN to MP_BINARY_OP_CONTAINS with swapped args.
     if (op == MP_BINARY_OP_IN) {
-        mp_obj_type_t *type = mp_obj_get_type(rhs);
-        if (type->binary_op != NULL) {
-            mp_obj_t res = type->binary_op(op, rhs, lhs);
-            if (res != MP_OBJ_NULL) {
-                return res;
-            }
-        }
-        if (type->getiter != NULL) {
-            /* second attempt, walk the iterator */
-            mp_obj_iter_buf_t iter_buf;
-            mp_obj_t iter = mp_getiter(rhs, &iter_buf);
-            mp_obj_t next;
-            while ((next = mp_iternext(iter)) != MP_OBJ_STOP_ITERATION) {
-                if (mp_obj_equal(next, lhs)) {
-                    return mp_const_true;
-                }
-            }
-            return mp_const_false;
-        }
-
-        if (MICROPY_ERROR_REPORTING == MICROPY_ERROR_REPORTING_TERSE) {
-            mp_raise_TypeError("object not iterable");
-        } else {
-            mp_raise_TypeError_varg(
-                "'%s' object is not iterable", mp_obj_get_type_str(rhs));
-        }
+        op = MP_BINARY_OP_CONTAINS;
+        mp_obj_t temp = lhs;
+        lhs = rhs;
+        rhs = temp;
     }
 
     // generic binary_op supplied by type
@@ -615,6 +589,20 @@ generic_binary_op:
     }
 #endif
 
+    if (op == MP_BINARY_OP_CONTAINS) {
+        // If type didn't support containment then explicitly walk the iterator.
+        // mp_getiter will raise the appropriate exception if lhs is not iterable.
+        mp_obj_iter_buf_t iter_buf;
+        mp_obj_t iter = mp_getiter(lhs, &iter_buf);
+        mp_obj_t next;
+        while ((next = mp_iternext(iter)) != MP_OBJ_STOP_ITERATION) {
+            if (mp_obj_equal(next, rhs)) {
+                return mp_const_true;
+            }
+        }
+        return mp_const_false;
+    }
+
 unsupported_op:
     if (MICROPY_ERROR_REPORTING == MICROPY_ERROR_REPORTING_TERSE) {
         mp_raise_TypeError("unsupported type for operator");
@@ -712,7 +700,7 @@ void mp_call_prepare_args_n_kw_var(bool have_self, size_t n_args_n_kw, const mp_
 
         // allocate memory for the new array of args
         args2_alloc = 1 + n_args + 2 * (n_kw + kw_dict_len);
-        args2 = m_new(mp_obj_t, args2_alloc);
+        args2 = mp_nonlocal_alloc(args2_alloc * sizeof(mp_obj_t));
 
         // copy the self
         if (self != MP_OBJ_NULL) {
@@ -733,7 +721,7 @@ void mp_call_prepare_args_n_kw_var(bool have_self, size_t n_args_n_kw, const mp_
 
         // allocate memory for the new array of args
         args2_alloc = 1 + n_args + len + 2 * (n_kw + kw_dict_len);
-        args2 = m_new(mp_obj_t, args2_alloc);
+        args2 = mp_nonlocal_alloc(args2_alloc * sizeof(mp_obj_t));
 
         // copy the self
         if (self != MP_OBJ_NULL) {
@@ -749,7 +737,7 @@ void mp_call_prepare_args_n_kw_var(bool have_self, size_t n_args_n_kw, const mp_
 
         // allocate memory for the new array of args
         args2_alloc = 1 + n_args + 2 * (n_kw + kw_dict_len) + 3;
-        args2 = m_new(mp_obj_t, args2_alloc);
+        args2 = mp_nonlocal_alloc(args2_alloc * sizeof(mp_obj_t));
 
         // copy the self
         if (self != MP_OBJ_NULL) {
@@ -766,7 +754,7 @@ void mp_call_prepare_args_n_kw_var(bool have_self, size_t n_args_n_kw, const mp_
         mp_obj_t item;
         while ((item = mp_iternext(iterable)) != MP_OBJ_STOP_ITERATION) {
             if (args2_len >= args2_alloc) {
-                args2 = m_renew(mp_obj_t, args2, args2_alloc, args2_alloc * 2);
+                args2 = mp_nonlocal_realloc(args2, args2_alloc * sizeof(mp_obj_t), args2_alloc * 2 * sizeof(mp_obj_t));
                 args2_alloc *= 2;
             }
             args2[args2_len++] = item;
@@ -792,8 +780,8 @@ void mp_call_prepare_args_n_kw_var(bool have_self, size_t n_args_n_kw, const mp_
             if (MP_MAP_SLOT_IS_FILLED(map, i)) {
                 // the key must be a qstr, so intern it if it's a string
                 mp_obj_t key = map->table[i].key;
-                if (MP_OBJ_IS_TYPE(key, &mp_type_str)) {
-                    key = mp_obj_str_intern(key);
+                if (!MP_OBJ_IS_QSTR(key)) {
+                    key = mp_obj_str_intern_checked(key);
                 }
                 args2[args2_len++] = key;
                 args2[args2_len++] = map->table[i].value;
@@ -817,13 +805,13 @@ void mp_call_prepare_args_n_kw_var(bool have_self, size_t n_args_n_kw, const mp_
                 if (new_alloc < 4) {
                     new_alloc = 4;
                 }
-                args2 = m_renew(mp_obj_t, args2, args2_alloc, new_alloc);
+                args2 = mp_nonlocal_realloc(args2, args2_alloc * sizeof(mp_obj_t), new_alloc * sizeof(mp_obj_t));
                 args2_alloc = new_alloc;
             }
 
             // the key must be a qstr, so intern it if it's a string
-            if (MP_OBJ_IS_TYPE(key, &mp_type_str)) {
-                key = mp_obj_str_intern(key);
+            if (!MP_OBJ_IS_QSTR(key)) {
+                key = mp_obj_str_intern_checked(key);
             }
 
             // get the value corresponding to the key
@@ -849,7 +837,7 @@ mp_obj_t mp_call_method_n_kw_var(bool have_self, size_t n_args_n_kw, const mp_ob
     mp_call_prepare_args_n_kw_var(have_self, n_args_n_kw, args, &out_args);
 
     mp_obj_t res = mp_call_function_n_kw(out_args.fun, out_args.n_args, out_args.n_kw, out_args.args);
-    m_del(mp_obj_t, out_args.args, out_args.n_alloc);
+    mp_nonlocal_free(out_args.args, out_args.n_alloc * sizeof(mp_obj_t));
 
     return res;
 }
@@ -1144,6 +1132,22 @@ void mp_load_method(mp_obj_t base, qstr attr, mp_obj_t *dest) {
     }
 }
 
+// Acts like mp_load_method_maybe but catches AttributeError, and all other exceptions if requested
+void mp_load_method_protected(mp_obj_t obj, qstr attr, mp_obj_t *dest, bool catch_all_exc) {
+    nlr_buf_t nlr;
+    if (nlr_push(&nlr) == 0) {
+        mp_load_method_maybe(obj, attr, dest);
+        nlr_pop();
+    } else {
+        if (!catch_all_exc
+            && !mp_obj_is_subclass_fast(MP_OBJ_FROM_PTR(((mp_obj_base_t*)nlr.ret_val)->type),
+                MP_OBJ_FROM_PTR(&mp_type_AttributeError))) {
+            // Re-raise the exception
+            nlr_raise(MP_OBJ_FROM_PTR(nlr.ret_val));
+        }
+    }
+}
+
 void mp_store_attr(mp_obj_t base, qstr attr, mp_obj_t value) {
     DEBUG_OP_printf("store attr %p.%s <- %p\n", base, qstr_str(attr), value);
     mp_obj_type_t *type = mp_obj_get_type(base);
@@ -1304,13 +1308,12 @@ mp_vm_return_kind_t mp_resume(mp_obj_t self_in, mp_obj_t send_value, mp_obj_t th
 
     if (type->iternext != NULL && send_value == mp_const_none) {
         mp_obj_t ret = type->iternext(self_in);
+        *ret_val = ret;
         if (ret != MP_OBJ_STOP_ITERATION) {
-            *ret_val = ret;
             return MP_VM_RETURN_YIELD;
         } else {
             // Emulate raise StopIteration()
             // Special case, handled in vm.c
-            *ret_val = MP_OBJ_NULL;
             return MP_VM_RETURN_NORMAL;
         }
     }
@@ -1372,7 +1375,7 @@ mp_vm_return_kind_t mp_resume(mp_obj_t self_in, mp_obj_t send_value, mp_obj_t th
         // will be propagated up. This behavior is approved by test_pep380.py
         // test_delegation_of_close_to_non_generator(),
         //  test_delegating_throw_to_non_generator()
-        *ret_val = throw_value;
+        *ret_val = mp_make_raise_obj(throw_value);
         return MP_VM_RETURN_EXCEPTION;
     }
 }
@@ -1426,6 +1429,8 @@ import_error:
         return dest[0];
     }
 
+    #if MICROPY_ENABLE_EXTERNAL_IMPORT
+
     // See if it's a package, then can try FS import
     if (!mp_obj_is_package(module)) {
         goto import_error;
@@ -1436,11 +1441,12 @@ import_error:
     const char *pkg_name = mp_obj_str_get_data(dest[0], &pkg_name_len);
 
     const uint dot_name_len = pkg_name_len + 1 + qstr_len(name);
-    char *dot_name = alloca(dot_name_len);
+    char *dot_name = mp_local_alloc(dot_name_len);
     memcpy(dot_name, pkg_name, pkg_name_len);
     dot_name[pkg_name_len] = '.';
     memcpy(dot_name + pkg_name_len + 1, qstr_str(name), qstr_len(name));
     qstr dot_name_q = qstr_from_strn(dot_name, dot_name_len);
+    mp_local_free(dot_name);
 
     mp_obj_t args[5];
     args[0] = MP_OBJ_NEW_QSTR(dot_name_q);
@@ -1451,6 +1457,13 @@ import_error:
 
     // TODO lookup __import__ and call that instead of going straight to builtin implementation
     return mp_builtin___import__(5, args);
+
+    #else
+
+    // Package import not supported with external imports disabled
+    goto import_error;
+
+    #endif
 }
 
 void mp_import_all(mp_obj_t module) {
@@ -1585,3 +1598,10 @@ NORETURN void mp_raise_OSError(int errno_) {
 NORETURN void mp_raise_NotImplementedError(const char *msg) {
     mp_raise_msg(&mp_type_NotImplementedError, msg);
 }
+
+#if MICROPY_STACK_CHECK || MICROPY_ENABLE_PYSTACK
+NORETURN void mp_raise_recursion_depth(void) {
+    nlr_raise(mp_obj_new_exception_arg1(&mp_type_RuntimeError,
+        MP_OBJ_NEW_QSTR(MP_QSTR_maximum_space_recursion_space_depth_space_exceeded)));
+}
+#endif
diff --git a/py/runtime.h b/py/runtime.h
index a8b6312ff..9e860df15 100644
--- a/py/runtime.h
+++ b/py/runtime.h
@@ -27,6 +27,7 @@
 #define MICROPY_INCLUDED_PY_RUNTIME_H
 
 #include "py/mpstate.h"
+#include "py/pystack.h"
 
 typedef enum {
     MP_VM_RETURN_NORMAL,
@@ -106,8 +107,9 @@ mp_obj_t mp_call_method_n_kw(size_t n_args, size_t n_kw, const mp_obj_t *args);
 mp_obj_t mp_call_method_n_kw_var(bool have_self, size_t n_args_n_kw, const mp_obj_t *args);
 mp_obj_t mp_call_method_self_n_kw(mp_obj_t meth, mp_obj_t self, size_t n_args, size_t n_kw, const mp_obj_t *args);
 // Call function and catch/dump exception - for Python callbacks from C code
-void mp_call_function_1_protected(mp_obj_t fun, mp_obj_t arg);
-void mp_call_function_2_protected(mp_obj_t fun, mp_obj_t arg1, mp_obj_t arg2);
+// (return MP_OBJ_NULL in case of exception).
+mp_obj_t mp_call_function_1_protected(mp_obj_t fun, mp_obj_t arg);
+mp_obj_t mp_call_function_2_protected(mp_obj_t fun, mp_obj_t arg1, mp_obj_t arg2);
 
 typedef struct _mp_call_args_t {
     mp_obj_t fun;
@@ -130,6 +132,7 @@ mp_obj_t mp_load_attr(mp_obj_t base, qstr attr);
 void mp_convert_member_lookup(mp_obj_t obj, const mp_obj_type_t *type, mp_obj_t member, mp_obj_t *dest);
 void mp_load_method(mp_obj_t base, qstr attr, mp_obj_t *dest);
 void mp_load_method_maybe(mp_obj_t base, qstr attr, mp_obj_t *dest);
+void mp_load_method_protected(mp_obj_t obj, qstr attr, mp_obj_t *dest, bool catch_all_exc);
 void mp_load_super_method(qstr attr, mp_obj_t *dest);
 void mp_store_attr(mp_obj_t base, qstr attr, mp_obj_t val);
 
@@ -155,8 +158,7 @@ NORETURN void mp_raise_RuntimeError(const char *msg);
 NORETURN void mp_raise_ImportError(const char *msg);
 NORETURN void mp_raise_IndexError(const char *msg);
 NORETURN void mp_raise_OSError(int errno_);
-NORETURN void mp_raise_NotImplementedError(const char *msg);
-NORETURN void mp_exc_recursion_depth(void);
+NORETURN void mp_raise_recursion_depth(void);
 
 #if MICROPY_BUILTIN_METHOD_CHECK_SELF_ARG
 #undef mp_check_self
diff --git a/py/runtime0.h b/py/runtime0.h
index 4709430fb..16434b315 100644
--- a/py/runtime0.h
+++ b/py/runtime0.h
@@ -133,6 +133,10 @@ typedef enum {
         #endif
     ,
 
+    // The runtime will convert MP_BINARY_OP_IN to this operator with swapped args.
+    // A type should implement this containment operator instead of MP_BINARY_OP_IN.
+    MP_BINARY_OP_CONTAINS,
+
     MP_BINARY_OP_NUM_RUNTIME,
 
     // These 2 are not supported by the runtime and must be synthesised by the emitter
@@ -162,8 +166,8 @@ typedef enum {
     MP_F_BUILD_MAP,
     MP_F_STORE_MAP,
 #if MICROPY_PY_BUILTINS_SET
-    MP_F_BUILD_SET,
     MP_F_STORE_SET,
+    MP_F_BUILD_SET,
 #endif
     MP_F_MAKE_FUNCTION_FROM_RAW_CODE,
     MP_F_NATIVE_CALL_FUNCTION_N_KW,
diff --git a/py/runtime_utils.c b/py/runtime_utils.c
index bcf3cbf7b..fd3f07111 100644
--- a/py/runtime_utils.c
+++ b/py/runtime_utils.c
@@ -28,22 +28,26 @@
 #include "py/mpconfig.h"
 #include "py/runtime.h"
 
-MP_NOINLINE void mp_call_function_1_protected(mp_obj_t fun, mp_obj_t arg) {
+MP_NOINLINE mp_obj_t mp_call_function_1_protected(mp_obj_t fun, mp_obj_t arg) {
     nlr_buf_t nlr;
     if (nlr_push(&nlr) == 0) {
-        mp_call_function_1(fun, arg);
+        mp_obj_t ret = mp_call_function_1(fun, arg);
         nlr_pop();
+        return ret;
     } else {
         mp_obj_print_exception(&mp_plat_print, MP_OBJ_FROM_PTR(nlr.ret_val));
+        return MP_OBJ_NULL;
     }
 }
 
-void mp_call_function_2_protected(mp_obj_t fun, mp_obj_t arg1, mp_obj_t arg2) {
+mp_obj_t mp_call_function_2_protected(mp_obj_t fun, mp_obj_t arg1, mp_obj_t arg2) {
     nlr_buf_t nlr;
     if (nlr_push(&nlr) == 0) {
-        mp_call_function_2(fun, arg1, arg2);
+        mp_obj_t ret = mp_call_function_2(fun, arg1, arg2);
         nlr_pop();
+        return ret;
     } else {
         mp_obj_print_exception(&mp_plat_print, MP_OBJ_FROM_PTR(nlr.ret_val));
+        return MP_OBJ_NULL;
     }
 }
diff --git a/py/smallint.h b/py/smallint.h
index 42679a78f..6a3c75236 100644
--- a/py/smallint.h
+++ b/py/smallint.h
@@ -50,10 +50,10 @@
 
 #elif MICROPY_OBJ_REPR == MICROPY_OBJ_REPR_D
 
-#define MP_SMALL_INT_MIN ((mp_int_t)(((mp_int_t)0xffffffff80000000) >> 1))
-#define MP_SMALL_INT_FITS(n) ((((n) ^ ((n) << 1)) & 0xffffffff80000000) == 0)
+#define MP_SMALL_INT_MIN ((mp_int_t)(((mp_int_t)0xffff800000000000) >> 1))
+#define MP_SMALL_INT_FITS(n) ((((n) ^ ((n) << 1)) & 0xffff800000000000) == 0)
 // Mask to truncate mp_int_t to positive value
-#define MP_SMALL_INT_POSITIVE_MASK ~(0xffffffff80000000 | (0xffffffff80000000 >> 1))
+#define MP_SMALL_INT_POSITIVE_MASK ~(0xffff800000000000 | (0xffff800000000000 >> 1))
 
 #endif
 
diff --git a/py/stackctrl.c b/py/stackctrl.c
index b4ec15b0d..46cbefc8c 100644
--- a/py/stackctrl.c
+++ b/py/stackctrl.c
@@ -52,13 +52,9 @@ void mp_stack_set_limit(mp_uint_t limit) {
     MP_STATE_THREAD(stack_limit) = limit;
 }
 
-void mp_exc_recursion_depth(void) {
-    mp_raise_RuntimeError("maximum recursion depth exceeded");
-}
-
 void mp_stack_check(void) {
     if (mp_stack_usage() >= MP_STATE_THREAD(stack_limit)) {
-        mp_exc_recursion_depth();
+        mp_raise_recursion_depth();
     }
 }
 
diff --git a/py/stream.c b/py/stream.c
index 453dee769..448de41bb 100644
--- a/py/stream.c
+++ b/py/stream.c
@@ -32,13 +32,6 @@
 #include "py/stream.h"
 #include "py/runtime.h"
 
-#if MICROPY_STREAMS_NON_BLOCK
-#include <errno.h>
-#if defined(__MINGW32__) && !defined(__MINGW64_VERSION_MAJOR)
-#define EWOULDBLOCK 140
-#endif
-#endif
-
 // This file defines generic Python stream read/write methods which
 // dispatch to the underlying stream interface of an object.
 
@@ -54,10 +47,9 @@ STATIC mp_obj_t stream_readall(mp_obj_t self_in);
 // be equal to input size).
 mp_uint_t mp_stream_rw(mp_obj_t stream, void *buf_, mp_uint_t size, int *errcode, byte flags) {
     byte *buf = buf_;
-    mp_obj_base_t* s = (mp_obj_base_t*)MP_OBJ_TO_PTR(stream);
     typedef mp_uint_t (*io_func_t)(mp_obj_t obj, void *buf, mp_uint_t size, int *errcode);
     io_func_t io_func;
-    const mp_stream_p_t *stream_p = s->type->protocol;
+    const mp_stream_p_t *stream_p = mp_get_stream(stream);
     if (flags & MP_STREAM_RW_WRITE) {
         io_func = (io_func_t)stream_p->write;
     } else {
@@ -105,16 +97,7 @@ const mp_stream_p_t *mp_get_stream_raise(mp_obj_t self_in, int flags) {
     return stream_p;
 }
 
-mp_obj_t mp_stream_close(mp_obj_t stream) {
-    // TODO: Still consider using ioctl for close
-    mp_obj_t dest[2];
-    mp_load_method(stream, MP_QSTR_close, dest);
-    return mp_call_method_n_kw(0, 0, dest);
-}
-
 STATIC mp_obj_t stream_read_generic(size_t n_args, const mp_obj_t *args, byte flags) {
-    const mp_stream_p_t *stream_p = mp_get_stream_raise(args[0], MP_STREAM_OP_READ);
-
     // What to do if sz < -1?  Python docs don't specify this case.
     // CPython does a readall, but here we silently let negatives through,
     // and they will cause a MemoryError.
@@ -123,6 +106,8 @@ STATIC mp_obj_t stream_read_generic(size_t n_args, const mp_obj_t *args, byte fl
         return stream_readall(args[0]);
     }
 
+    const mp_stream_p_t *stream_p = mp_get_stream(args[0]);
+
     #if MICROPY_PY_BUILTINS_STR_UNICODE
     if (stream_p->is_text) {
         // We need to read sz number of unicode characters.  Because we don't have any
@@ -241,8 +226,6 @@ STATIC mp_obj_t stream_read1(size_t n_args, const mp_obj_t *args) {
 MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mp_stream_read1_obj, 1, 2, stream_read1);
 
 mp_obj_t mp_stream_write(mp_obj_t self_in, const void *buf, size_t len, byte flags) {
-    mp_get_stream_raise(self_in, MP_STREAM_OP_WRITE);
-
     int error;
     mp_uint_t out_sz = mp_stream_rw(self_in, (void*)buf, len, &error, flags);
     if (error != 0) {
@@ -258,7 +241,7 @@ mp_obj_t mp_stream_write(mp_obj_t self_in, const void *buf, size_t len, byte fla
     }
 }
 
-// XXX hack
+// This is used to adapt a stream object to an mp_print_t interface
 void mp_stream_write_adaptor(void *self, const char *buf, size_t len) {
     mp_stream_write(MP_OBJ_FROM_PTR(self), buf, len, MP_STREAM_RW_WRITE);
 }
@@ -290,7 +273,6 @@ STATIC mp_obj_t stream_write1_method(mp_obj_t self_in, mp_obj_t arg) {
 MP_DEFINE_CONST_FUN_OBJ_2(mp_stream_write1_obj, stream_write1_method);
 
 STATIC mp_obj_t stream_readinto(size_t n_args, const mp_obj_t *args) {
-    mp_get_stream_raise(args[0], MP_STREAM_OP_READ);
     mp_buffer_info_t bufinfo;
     mp_get_buffer_raise(args[1], &bufinfo, MP_BUFFER_WRITE);
 
@@ -319,7 +301,7 @@ STATIC mp_obj_t stream_readinto(size_t n_args, const mp_obj_t *args) {
 MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mp_stream_readinto_obj, 2, 3, stream_readinto);
 
 STATIC mp_obj_t stream_readall(mp_obj_t self_in) {
-    const mp_stream_p_t *stream_p = mp_get_stream_raise(self_in, MP_STREAM_OP_READ);
+    const mp_stream_p_t *stream_p = mp_get_stream(self_in);
 
     mp_uint_t total_size = 0;
     vstr_t vstr;
@@ -360,7 +342,7 @@ STATIC mp_obj_t stream_readall(mp_obj_t self_in) {
 
 // Unbuffered, inefficient implementation of readline() for raw I/O files.
 STATIC mp_obj_t stream_unbuffered_readline(size_t n_args, const mp_obj_t *args) {
-    const mp_stream_p_t *stream_p = mp_get_stream_raise(args[0], MP_STREAM_OP_READ);
+    const mp_stream_p_t *stream_p = mp_get_stream(args[0]);
 
     mp_int_t max_size = -1;
     if (n_args > 1) {
@@ -434,9 +416,18 @@ mp_obj_t mp_stream_unbuffered_iter(mp_obj_t self) {
     return MP_OBJ_STOP_ITERATION;
 }
 
-STATIC mp_obj_t stream_seek(size_t n_args, const mp_obj_t *args) {
-    const mp_stream_p_t *stream_p = mp_get_stream_raise(args[0], MP_STREAM_OP_IOCTL);
+mp_obj_t mp_stream_close(mp_obj_t stream) {
+    const mp_stream_p_t *stream_p = mp_get_stream(stream);
+    int error;
+    mp_uint_t res = stream_p->ioctl(stream, MP_STREAM_CLOSE, 0, &error);
+    if (res == MP_STREAM_ERROR) {
+        mp_raise_OSError(error);
+    }
+    return mp_const_none;
+}
+MP_DEFINE_CONST_FUN_OBJ_1(mp_stream_close_obj, mp_stream_close);
 
+STATIC mp_obj_t stream_seek(size_t n_args, const mp_obj_t *args) {
     struct mp_stream_seek_t seek_s;
     // TODO: Could be uint64
     seek_s.offset = mp_obj_get_int(args[1]);
@@ -450,6 +441,7 @@ STATIC mp_obj_t stream_seek(size_t n_args, const mp_obj_t *args) {
         mp_raise_OSError(MP_EINVAL);
     }
 
+    const mp_stream_p_t *stream_p = mp_get_stream(args[0]);
     int error;
     mp_uint_t res = stream_p->ioctl(args[0], MP_STREAM_SEEK, (mp_uint_t)(uintptr_t)&seek_s, &error);
     if (res == MP_STREAM_ERROR) {
@@ -470,7 +462,7 @@ STATIC mp_obj_t stream_tell(mp_obj_t self) {
 MP_DEFINE_CONST_FUN_OBJ_1(mp_stream_tell_obj, stream_tell);
 
 STATIC mp_obj_t stream_flush(mp_obj_t self) {
-    const mp_stream_p_t *stream_p = mp_get_stream_raise(self, MP_STREAM_OP_IOCTL);
+    const mp_stream_p_t *stream_p = mp_get_stream(self);
     int error;
     mp_uint_t res = stream_p->ioctl(self, MP_STREAM_FLUSH, 0, &error);
     if (res == MP_STREAM_ERROR) {
@@ -481,8 +473,6 @@ STATIC mp_obj_t stream_flush(mp_obj_t self) {
 MP_DEFINE_CONST_FUN_OBJ_1(mp_stream_flush_obj, stream_flush);
 
 STATIC mp_obj_t stream_ioctl(size_t n_args, const mp_obj_t *args) {
-    const mp_stream_p_t *stream_p = mp_get_stream_raise(args[0], MP_STREAM_OP_IOCTL);
-
     mp_buffer_info_t bufinfo;
     uintptr_t val = 0;
     if (n_args > 2) {
@@ -493,6 +483,7 @@ STATIC mp_obj_t stream_ioctl(size_t n_args, const mp_obj_t *args) {
         }
     }
 
+    const mp_stream_p_t *stream_p = mp_get_stream(args[0]);
     int error;
     mp_uint_t res = stream_p->ioctl(args[0], mp_obj_get_int(args[1]), val, &error);
     if (res == MP_STREAM_ERROR) {
diff --git a/py/stream.h b/py/stream.h
index fbe3d7d85..7b953138c 100644
--- a/py/stream.h
+++ b/py/stream.h
@@ -35,7 +35,7 @@
 #define MP_STREAM_FLUSH (1)
 #define MP_STREAM_SEEK  (2)
 #define MP_STREAM_POLL  (3)
-//#define MP_STREAM_CLOSE       (4)  // Not yet implemented
+#define MP_STREAM_CLOSE         (4)
 #define MP_STREAM_TIMEOUT       (5)  // Get/set timeout (single op)
 #define MP_STREAM_GET_OPTS      (6)  // Get stream options
 #define MP_STREAM_SET_OPTS      (7)  // Set stream options
@@ -62,6 +62,16 @@ struct mp_stream_seek_t {
 #define MP_SEEK_CUR (1)
 #define MP_SEEK_END (2)
 
+// Stream protocol
+typedef struct _mp_stream_p_t {
+    // On error, functions should return MP_STREAM_ERROR and fill in *errcode (values
+    // are implementation-dependent, but will be exposed to user, e.g. via exception).
+    mp_uint_t (*read)(mp_obj_t obj, void *buf, mp_uint_t size, int *errcode);
+    mp_uint_t (*write)(mp_obj_t obj, const void *buf, mp_uint_t size, int *errcode);
+    mp_uint_t (*ioctl)(mp_obj_t obj, mp_uint_t request, uintptr_t arg, int *errcode);
+    mp_uint_t is_text : 1; // default is bytes, set this for text stream
+} mp_stream_p_t;
+
 MP_DECLARE_CONST_FUN_OBJ_VAR_BETWEEN(mp_stream_read_obj);
 MP_DECLARE_CONST_FUN_OBJ_VAR_BETWEEN(mp_stream_read1_obj);
 MP_DECLARE_CONST_FUN_OBJ_VAR_BETWEEN(mp_stream_readinto_obj);
@@ -69,6 +79,7 @@ MP_DECLARE_CONST_FUN_OBJ_VAR_BETWEEN(mp_stream_unbuffered_readline_obj);
 MP_DECLARE_CONST_FUN_OBJ_1(mp_stream_unbuffered_readlines_obj);
 MP_DECLARE_CONST_FUN_OBJ_VAR_BETWEEN(mp_stream_write_obj);
 MP_DECLARE_CONST_FUN_OBJ_2(mp_stream_write1_obj);
+MP_DECLARE_CONST_FUN_OBJ_1(mp_stream_close_obj);
 MP_DECLARE_CONST_FUN_OBJ_VAR_BETWEEN(mp_stream_seek_obj);
 MP_DECLARE_CONST_FUN_OBJ_1(mp_stream_tell_obj);
 MP_DECLARE_CONST_FUN_OBJ_1(mp_stream_flush_obj);
@@ -79,6 +90,11 @@ MP_DECLARE_CONST_FUN_OBJ_VAR_BETWEEN(mp_stream_ioctl_obj);
 #define MP_STREAM_OP_WRITE (2)
 #define MP_STREAM_OP_IOCTL (4)
 
+// Object is assumed to have a non-NULL stream protocol with valid r/w/ioctl methods
+static inline const mp_stream_p_t *mp_get_stream(mp_const_obj_t self) {
+    return (const mp_stream_p_t*)((const mp_obj_base_t*)MP_OBJ_TO_PTR(self))->type->protocol;
+}
+
 const mp_stream_p_t *mp_get_stream_raise(mp_obj_t self_in, int flags);
 mp_obj_t mp_stream_close(mp_obj_t stream);
 
@@ -106,7 +122,7 @@ int mp_stream_posix_fsync(mp_obj_t stream);
 #endif
 
 #if MICROPY_STREAMS_NON_BLOCK
-#define mp_is_nonblocking_error(errno) ((errno) == EAGAIN || (errno) == EWOULDBLOCK)
+#define mp_is_nonblocking_error(errno) ((errno) == MP_EAGAIN || (errno) == MP_EWOULDBLOCK)
 #else
 #define mp_is_nonblocking_error(errno) (0)
 #endif
diff --git a/py/unicode.c b/py/unicode.c
index 140b7ba71..935dc9012 100644
--- a/py/unicode.c
+++ b/py/unicode.c
@@ -67,9 +67,9 @@ STATIC const uint8_t attr[] = {
     AT_LO, AT_LO, AT_LO, AT_PR, AT_PR, AT_PR, AT_PR, 0
 };
 
-// TODO: Rename to str_get_char
-unichar utf8_get_char(const byte *s) {
 #if MICROPY_PY_BUILTINS_STR_UNICODE
+
+unichar utf8_get_char(const byte *s) {
     unichar ord = *s++;
     if (!UTF8_IS_NONASCII(ord)) return ord;
     ord &= 0x7F;
@@ -80,22 +80,14 @@ unichar utf8_get_char(const byte *s) {
         ord = (ord << 6) | (*s++ & 0x3F);
     }
     return ord;
-#else
-    return *s;
-#endif
 }
 
-// TODO: Rename to str_next_char
 const byte *utf8_next_char(const byte *s) {
-#if MICROPY_PY_BUILTINS_STR_UNICODE
     ++s;
     while (UTF8_IS_CONT(*s)) {
         ++s;
     }
     return s;
-#else
-    return s + 1;
-#endif
 }
 
 mp_uint_t utf8_ptr_to_index(const byte *s, const byte *ptr) {
@@ -109,21 +101,18 @@ mp_uint_t utf8_ptr_to_index(const byte *s, const byte *ptr) {
     return i;
 }
 
-// TODO: Rename to str_charlen
-mp_uint_t unichar_charlen(const char *str, mp_uint_t len) {
-#if MICROPY_PY_BUILTINS_STR_UNICODE
-    mp_uint_t charlen = 0;
-    for (const char *top = str + len; str < top; ++str) {
+size_t utf8_charlen(const byte *str, size_t len) {
+    size_t charlen = 0;
+    for (const byte *top = str + len; str < top; ++str) {
         if (!UTF8_IS_CONT(*str)) {
             ++charlen;
         }
     }
     return charlen;
-#else
-    return len;
-#endif
 }
 
+#endif
+
 // Be aware: These unichar_is* functions are actually ASCII-only!
 bool unichar_isspace(unichar c) {
     return c < 128 && (attr[c] & FL_SPACE) != 0;
@@ -183,6 +172,8 @@ mp_uint_t unichar_xdigit_value(unichar c) {
     return n;
 }
 
+#if MICROPY_PY_BUILTINS_STR_UNICODE
+
 bool utf8_check(const byte *p, size_t len) {
     uint8_t need = 0;
     const byte *end = p + len;
@@ -210,3 +201,5 @@ bool utf8_check(const byte *p, size_t len) {
     }
     return need == 0; // no pending fragments allowed
 }
+
+#endif
diff --git a/py/vm.c b/py/vm.c
index 564200037..498ecb491 100644
--- a/py/vm.c
+++ b/py/vm.c
@@ -48,14 +48,6 @@
 // top element.
 // Exception stack also grows up, top element is also pointed at.
 
-// Exception stack unwind reasons (WHY_* in CPython-speak)
-// TODO perhaps compress this to RETURN=0, JUMP>0, with number of unwinds
-// left to do encoded in the JUMP number
-typedef enum {
-    UNWIND_RETURN = 1,
-    UNWIND_JUMP,
-} mp_unwind_reason_t;
-
 #define DECODE_UINT \
     mp_uint_t unum = 0; \
     do { \
@@ -144,7 +136,7 @@ mp_vm_return_kind_t mp_execute_bytecode(mp_code_state_t *code_state, volatile mp
     #define ENTRY(op) entry_##op
     #define ENTRY_DEFAULT entry_default
 #else
-    #define DISPATCH() break
+    #define DISPATCH() goto dispatch_loop
     #define DISPATCH_WITH_PEND_EXC_CHECK() goto pending_exception_check
     #define ENTRY(op) case op
     #define ENTRY_DEFAULT default
@@ -344,7 +336,7 @@ dispatch_loop:
                     MARK_EXC_IP_SELECTIVE();
                     DECODE_QSTR;
                     mp_obj_t top = TOP();
-                    if (mp_obj_get_type(top)->attr == mp_obj_instance_attr) {
+                    if (mp_obj_is_instance_type(mp_obj_get_type(top))) {
                         mp_obj_instance_t *self = MP_OBJ_TO_PTR(top);
                         mp_uint_t x = *ip;
                         mp_obj_t key = MP_OBJ_NEW_QSTR(qst);
@@ -442,7 +434,7 @@ dispatch_loop:
                     MARK_EXC_IP_SELECTIVE();
                     DECODE_QSTR;
                     mp_obj_t top = TOP();
-                    if (mp_obj_get_type(top)->attr == mp_obj_instance_attr && sp[-1] != MP_OBJ_NULL) {
+                    if (mp_obj_is_instance_type(mp_obj_get_type(top)) && sp[-1] != MP_OBJ_NULL) {
                         mp_obj_instance_t *self = MP_OBJ_TO_PTR(top);
                         mp_uint_t x = *ip;
                         mp_obj_t key = MP_OBJ_NEW_QSTR(qst);
@@ -613,29 +605,18 @@ dispatch_loop:
                         mp_call_method_n_kw(3, 0, sp);
                         SET_TOP(mp_const_none);
                     } else if (MP_OBJ_IS_SMALL_INT(TOP())) {
-                        mp_int_t cause_val = MP_OBJ_SMALL_INT_VALUE(TOP());
-                        if (cause_val == UNWIND_RETURN) {
-                            // stack: (..., __exit__, ctx_mgr, ret_val, UNWIND_RETURN)
-                            mp_obj_t ret_val = sp[-1];
-                            sp[-1] = mp_const_none;
-                            sp[0] = mp_const_none;
-                            sp[1] = mp_const_none;
-                            mp_call_method_n_kw(3, 0, sp - 3);
-                            sp[-3] = ret_val;
-                            sp[-2] = MP_OBJ_NEW_SMALL_INT(UNWIND_RETURN);
-                        } else {
-                            assert(cause_val == UNWIND_JUMP);
-                            // stack: (..., __exit__, ctx_mgr, dest_ip, num_exc, UNWIND_JUMP)
-                            mp_obj_t dest_ip = sp[-2];
-                            mp_obj_t num_exc = sp[-1];
-                            sp[-2] = mp_const_none;
-                            sp[-1] = mp_const_none;
-                            sp[0] = mp_const_none;
-                            mp_call_method_n_kw(3, 0, sp - 4);
-                            sp[-4] = dest_ip;
-                            sp[-3] = num_exc;
-                            sp[-2] = MP_OBJ_NEW_SMALL_INT(UNWIND_JUMP);
-                        }
+                        // Getting here there are two distinct cases:
+                        //  - unwind return, stack: (..., __exit__, ctx_mgr, ret_val, SMALL_INT(-1))
+                        //  - unwind jump, stack:   (..., __exit__, ctx_mgr, dest_ip, SMALL_INT(num_exc))
+                        // For both cases we do exactly the same thing.
+                        mp_obj_t data = sp[-1];
+                        mp_obj_t cause = sp[0];
+                        sp[-1] = mp_const_none;
+                        sp[0] = mp_const_none;
+                        sp[1] = mp_const_none;
+                        mp_call_method_n_kw(3, 0, sp - 3);
+                        sp[-3] = data;
+                        sp[-2] = cause;
                         sp -= 2; // we removed (__exit__, ctx_mgr)
                     } else {
                         assert(mp_obj_is_exception_instance(TOP()));
@@ -680,10 +661,11 @@ unwind_jump:;
                             // of a "with" block contains the context manager info.
                             // We're going to run "finally" code as a coroutine
                             // (not calling it recursively). Set up a sentinel
-                            // on a stack so it can return back to us when it is
+                            // on the stack so it can return back to us when it is
                             // done (when WITH_CLEANUP or END_FINALLY reached).
-                            PUSH((mp_obj_t)unum); // push number of exception handlers left to unwind
-                            PUSH(MP_OBJ_NEW_SMALL_INT(UNWIND_JUMP)); // push sentinel
+                            // The sentinel is the number of exception handlers left to
+                            // unwind, which is a non-negative integer.
+                            PUSH(MP_OBJ_NEW_SMALL_INT(unum));
                             ip = exc_sp->handler; // get exception handler byte code address
                             exc_sp--; // pop exception handler
                             goto dispatch_loop; // run the exception handler
@@ -720,11 +702,14 @@ unwind_jump:;
                     } else if (MP_OBJ_IS_SMALL_INT(TOP())) {
                         // We finished "finally" coroutine and now dispatch back
                         // to our caller, based on TOS value
-                        mp_unwind_reason_t reason = MP_OBJ_SMALL_INT_VALUE(POP());
-                        if (reason == UNWIND_RETURN) {
+                        mp_int_t cause = MP_OBJ_SMALL_INT_VALUE(POP());
+                        if (cause < 0) {
+                            // A negative cause indicates unwind return
                             goto unwind_return;
                         } else {
-                            assert(reason == UNWIND_JUMP);
+                            // Otherwise it's an unwind jump and we must push as a raw
+                            // number the number of exception handlers to unwind
+                            PUSH((mp_obj_t)cause);
                             goto unwind_jump;
                         }
                     } else {
@@ -926,18 +911,22 @@ unwind_jump:;
                         code_state->sp = sp;
                         code_state->exc_sp = MP_TAGPTR_MAKE(exc_sp, currently_in_except_block);
                         mp_code_state_t *new_state = mp_obj_fun_bc_prepare_codestate(*sp, unum & 0xff, (unum >> 8) & 0xff, sp + 1);
-                        if (new_state) {
+                        #if !MICROPY_ENABLE_PYSTACK
+                        if (new_state == NULL) {
+                            // Couldn't allocate codestate on heap: in the strict case raise
+                            // an exception, otherwise just fall through to stack allocation.
+                            #if MICROPY_STACKLESS_STRICT
+                        deep_recursion_error:
+                            mp_raise_recursion_depth();
+                            #endif
+                        } else
+                        #endif
+                        {
                             new_state->prev = code_state;
                             code_state = new_state;
                             nlr_pop();
                             goto run_code_state;
                         }
-                        #if MICROPY_STACKLESS_STRICT
-                        else {
-                        deep_recursion_error:
-                            mp_exc_recursion_depth();
-                        }
-                        #endif
                     }
                     #endif
                     SET_TOP(mp_call_function_n_kw(*sp, unum & 0xff, (unum >> 8) & 0xff, sp + 1));
@@ -963,18 +952,26 @@ unwind_jump:;
 
                         mp_code_state_t *new_state = mp_obj_fun_bc_prepare_codestate(out_args.fun,
                             out_args.n_args, out_args.n_kw, out_args.args);
-                        m_del(mp_obj_t, out_args.args, out_args.n_alloc);
-                        if (new_state) {
+                        #if !MICROPY_ENABLE_PYSTACK
+                        // Freeing args at this point does not follow a LIFO order so only do it if
+                        // pystack is not enabled.  For pystack, they are freed when code_state is.
+                        mp_nonlocal_free(out_args.args, out_args.n_alloc * sizeof(mp_obj_t));
+                        #endif
+                        #if !MICROPY_ENABLE_PYSTACK
+                        if (new_state == NULL) {
+                            // Couldn't allocate codestate on heap: in the strict case raise
+                            // an exception, otherwise just fall through to stack allocation.
+                            #if MICROPY_STACKLESS_STRICT
+                            goto deep_recursion_error;
+                            #endif
+                        } else
+                        #endif
+                        {
                             new_state->prev = code_state;
                             code_state = new_state;
                             nlr_pop();
                             goto run_code_state;
                         }
-                        #if MICROPY_STACKLESS_STRICT
-                        else {
-                            goto deep_recursion_error;
-                        }
-                        #endif
                     }
                     #endif
                     SET_TOP(mp_call_method_n_kw_var(false, unum, sp));
@@ -998,17 +995,21 @@ unwind_jump:;
                         int adjust = (sp[1] == MP_OBJ_NULL) ? 0 : 1;
 
                         mp_code_state_t *new_state = mp_obj_fun_bc_prepare_codestate(*sp, n_args + adjust, n_kw, sp + 2 - adjust);
-                        if (new_state) {
+                        #if !MICROPY_ENABLE_PYSTACK
+                        if (new_state == NULL) {
+                            // Couldn't allocate codestate on heap: in the strict case raise
+                            // an exception, otherwise just fall through to stack allocation.
+                            #if MICROPY_STACKLESS_STRICT
+                            goto deep_recursion_error;
+                            #endif
+                        } else
+                        #endif
+                        {
                             new_state->prev = code_state;
                             code_state = new_state;
                             nlr_pop();
                             goto run_code_state;
                         }
-                        #if MICROPY_STACKLESS_STRICT
-                        else {
-                            goto deep_recursion_error;
-                        }
-                        #endif
                     }
                     #endif
                     SET_TOP(mp_call_method_n_kw(unum & 0xff, (unum >> 8) & 0xff, sp));
@@ -1034,18 +1035,26 @@ unwind_jump:;
 
                         mp_code_state_t *new_state = mp_obj_fun_bc_prepare_codestate(out_args.fun,
                             out_args.n_args, out_args.n_kw, out_args.args);
-                        m_del(mp_obj_t, out_args.args, out_args.n_alloc);
-                        if (new_state) {
+                        #if !MICROPY_ENABLE_PYSTACK
+                        // Freeing args at this point does not follow a LIFO order so only do it if
+                        // pystack is not enabled.  For pystack, they are freed when code_state is.
+                        mp_nonlocal_free(out_args.args, out_args.n_alloc * sizeof(mp_obj_t));
+                        #endif
+                        #if !MICROPY_ENABLE_PYSTACK
+                        if (new_state == NULL) {
+                            // Couldn't allocate codestate on heap: in the strict case raise
+                            // an exception, otherwise just fall through to stack allocation.
+                            #if MICROPY_STACKLESS_STRICT
+                            goto deep_recursion_error;
+                            #endif
+                        } else
+                        #endif
+                        {
                             new_state->prev = code_state;
                             code_state = new_state;
                             nlr_pop();
                             goto run_code_state;
                         }
-                        #if MICROPY_STACKLESS_STRICT
-                        else {
-                            goto deep_recursion_error;
-                        }
-                        #endif
                     }
                     #endif
                     SET_TOP(mp_call_method_n_kw_var(true, unum, sp));
@@ -1081,7 +1090,7 @@ unwind_return:
                             // (not calling it recursively). Set up a sentinel
                             // on a stack so it can return back to us when it is
                             // done (when WITH_CLEANUP or END_FINALLY reached).
-                            PUSH(MP_OBJ_NEW_SMALL_INT(UNWIND_RETURN));
+                            PUSH(MP_OBJ_NEW_SMALL_INT(-1));
                             ip = exc_sp->handler;
                             exc_sp--;
                             goto dispatch_loop;
@@ -1096,7 +1105,15 @@ unwind_return:
                     if (code_state->prev != NULL) {
                         mp_obj_t res = *sp;
                         mp_globals_set(code_state->old_globals);
-                        code_state = code_state->prev;
+                        mp_code_state_t *new_code_state = code_state->prev;
+                        #if MICROPY_ENABLE_PYSTACK
+                        // Free code_state, and args allocated by mp_call_prepare_args_n_kw_var
+                        // (The latter is implicitly freed when using pystack due to its LIFO nature.)
+                        // The sizeof in the following statement does not include the size of the variable
+                        // part of the struct.  This arg is anyway not used if pystack is enabled.
+                        mp_nonlocal_free(code_state, sizeof(mp_code_state_t));
+                        #endif
+                        code_state = new_code_state;
                         *code_state->sp = res;
                         goto run_code_state;
                     }
@@ -1105,7 +1122,7 @@ unwind_return:
 
                 ENTRY(MP_BC_RAISE_VARARGS): {
                     MARK_EXC_IP_SELECTIVE();
-                    mp_uint_t unum = *ip++;
+                    mp_uint_t unum = *ip;
                     mp_obj_t obj;
                     if (unum == 2) {
                         mp_warning("exception chaining not supported");
@@ -1126,7 +1143,7 @@ unwind_return:
                             RAISE(obj);
                         }
                     } else {
-                        obj = POP();
+                        obj = TOP();
                     }
                     obj = mp_make_raise_obj(obj);
                     RAISE(obj);
@@ -1149,6 +1166,7 @@ yield:
                     mp_obj_t send_value = POP();
                     mp_obj_t t_exc = MP_OBJ_NULL;
                     mp_obj_t ret_value;
+                    code_state->sp = sp; // Save sp because it's needed if mp_resume raises StopIteration
                     if (inject_exc != MP_OBJ_NULL) {
                         t_exc = inject_exc;
                         inject_exc = MP_OBJ_NULL;
@@ -1164,8 +1182,7 @@ yield:
                     } else if (ret_kind == MP_VM_RETURN_NORMAL) {
                         // Pop exhausted gen
                         sp--;
-                        // TODO: When ret_value can be MP_OBJ_NULL here??
-                        if (ret_value == MP_OBJ_NULL || ret_value == MP_OBJ_STOP_ITERATION) {
+                        if (ret_value == MP_OBJ_STOP_ITERATION) {
                             // Optimize StopIteration
                             // TODO: get StopIteration's value
                             PUSH(mp_const_none);
@@ -1253,10 +1270,10 @@ yield:
                     } else if (ip[-1] < MP_BC_STORE_FAST_MULTI + 16) {
                         fastn[MP_BC_STORE_FAST_MULTI - (mp_int_t)ip[-1]] = POP();
                         DISPATCH();
-                    } else if (ip[-1] < MP_BC_UNARY_OP_MULTI + 7) {
+                    } else if (ip[-1] < MP_BC_UNARY_OP_MULTI + MP_UNARY_OP_NUM_BYTECODE) {
                         SET_TOP(mp_unary_op(ip[-1] - MP_BC_UNARY_OP_MULTI, TOP()));
                         DISPATCH();
-                    } else if (ip[-1] < MP_BC_BINARY_OP_MULTI + 36) {
+                    } else if (ip[-1] < MP_BC_BINARY_OP_MULTI + MP_BINARY_OP_NUM_BYTECODE) {
                         mp_obj_t rhs = POP();
                         mp_obj_t lhs = TOP();
                         SET_TOP(mp_binary_op(ip[-1] - MP_BC_BINARY_OP_MULTI, lhs, rhs));
@@ -1305,11 +1322,12 @@ pending_exception_check:
 
                 #if MICROPY_PY_THREAD_GIL
                 #if MICROPY_PY_THREAD_GIL_VM_DIVISOR
-                if (--gil_divisor == 0) {
-                    gil_divisor = MICROPY_PY_THREAD_GIL_VM_DIVISOR;
-                #else
-                {
+                if (--gil_divisor == 0)
                 #endif
+                {
+                    #if MICROPY_PY_THREAD_GIL_VM_DIVISOR
+                    gil_divisor = MICROPY_PY_THREAD_GIL_VM_DIVISOR;
+                    #endif
                     #if MICROPY_ENABLE_SCHEDULER
                     // can only switch threads if the scheduler is unlocked
                     if (MP_STATE_VM(sched_state) == MP_SCHED_IDLE)
@@ -1348,7 +1366,8 @@ exception_handler:
                     } else if (*code_state->ip == MP_BC_YIELD_FROM) {
                         // StopIteration inside yield from call means return a value of
                         // yield from, so inject exception's value as yield from's result
-                        *++code_state->sp = mp_obj_exception_get_value(MP_OBJ_FROM_PTR(nlr.ret_val));
+                        // (Instead of stack pop then push we just replace exhausted gen with value)
+                        *code_state->sp = mp_obj_exception_get_value(MP_OBJ_FROM_PTR(nlr.ret_val));
                         code_state->ip++; // yield from is over, move to next instruction
                         goto outer_dispatch_loop; // continue with dispatch loop
                     }
@@ -1361,8 +1380,7 @@ unwind_loop:
             // set file and line number that the exception occurred at
             // TODO: don't set traceback for exceptions re-raised by END_FINALLY.
             // But consider how to handle nested exceptions.
-            // TODO need a better way of not adding traceback to constant objects (right now, just GeneratorExit_obj and MemoryError_obj)
-            if (nlr.ret_val != &mp_const_GeneratorExit_obj && nlr.ret_val != &mp_const_MemoryError_obj) {
+            if (nlr.ret_val != &mp_const_GeneratorExit_obj) {
                 const byte *ip = code_state->fun_bc->bytecode;
                 ip = mp_decode_uint_skip(ip); // skip n_state
                 ip = mp_decode_uint_skip(ip); // skip n_exc_stack
@@ -1438,7 +1456,15 @@ unwind_loop:
             #if MICROPY_STACKLESS
             } else if (code_state->prev != NULL) {
                 mp_globals_set(code_state->old_globals);
-                code_state = code_state->prev;
+                mp_code_state_t *new_code_state = code_state->prev;
+                #if MICROPY_ENABLE_PYSTACK
+                // Free code_state, and args allocated by mp_call_prepare_args_n_kw_var
+                // (The latter is implicitly freed when using pystack due to its LIFO nature.)
+                // The sizeof in the following statement does not include the size of the variable
+                // part of the struct.  This arg is anyway not used if pystack is enabled.
+                mp_nonlocal_free(code_state, sizeof(mp_code_state_t));
+                #endif
+                code_state = new_code_state;
                 size_t n_state = mp_decode_uint_value(code_state->fun_bc->bytecode);
                 fastn = &code_state->state[n_state - 1];
                 exc_stack = (mp_exc_stack_t*)(code_state->state + n_state);