Support print("", flush=True)

Fixes #1127

3 files changed, 11 insertions, 3 deletions

diff --git a/py/modbuiltins.c b/py/modbuiltins.c
index e7ce7f998..b4f4fca34 100644
--- a/py/modbuiltins.c
+++ b/py/modbuiltins.c
@@ -371,10 +371,11 @@ 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 *pos_args, mp_map_t *kw_args) {
-    enum { ARG_sep, ARG_end, ARG_file };
+    enum { ARG_sep, ARG_end, ARG_flush, 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_)} },
+        { MP_QSTR_flush, MP_ARG_KW_ONLY | MP_ARG_BOOL, {.u_bool = false} },
         #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
@@ -414,6 +415,9 @@ STATIC mp_obj_t mp_builtin_print(size_t n_args, const mp_obj_t *pos_args, mp_map
     }
     #if MICROPY_PY_IO && MICROPY_PY_SYS_STDFILES
     mp_stream_write_adaptor(print.data, end_data, u.len[1]);
+    if (u.args[ARG_flush].u_bool) {
+        mp_stream_flush(MP_OBJ_FROM_PTR(print.data));
+    }
     #else
     mp_print_strn(&mp_plat_print, end_data, u.len[1], 0, 0, 0);
     #endif
diff --git a/py/stream.c b/py/stream.c
index 9d8be445c..08c749cc3 100644
--- a/py/stream.c
+++ b/py/stream.c
@@ -468,16 +468,19 @@ 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) {
+mp_obj_t mp_stream_flush(mp_obj_t self) {
     const mp_stream_p_t *stream_p = mp_get_stream(self);
     int error;
+    if (stream_p->ioctl == NULL) {
+        mp_raise_OSError(MP_EINVAL);
+    }
     mp_uint_t res = stream_p->ioctl(self, MP_STREAM_FLUSH, 0, &error);
     if (res == MP_STREAM_ERROR) {
         mp_raise_OSError(error);
     }
     return mp_const_none;
 }
-MP_DEFINE_CONST_FUN_OBJ_1(mp_stream_flush_obj, stream_flush);
+MP_DEFINE_CONST_FUN_OBJ_1(mp_stream_flush_obj, mp_stream_flush);
 
 STATIC mp_obj_t stream_ioctl(size_t n_args, const mp_obj_t *args) {
     mp_buffer_info_t bufinfo;
diff --git a/py/stream.h b/py/stream.h
index bcba4f234..03e24c746 100644
--- a/py/stream.h
+++ b/py/stream.h
@@ -113,6 +113,7 @@ mp_uint_t mp_stream_rw(mp_obj_t stream, void *buf, mp_uint_t size, int *errcode,
 #define mp_stream_read_exactly(stream, buf, size, err) mp_stream_rw(stream, buf, size, err, MP_STREAM_RW_READ)
 
 void mp_stream_write_adaptor(void *self, const char *buf, size_t len);
+mp_obj_t mp_stream_flush(mp_obj_t self);
 
 #if MICROPY_STREAMS_POSIX_API
 // Functions with POSIX-compatible signatures