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2017-11-16tests: Fixup tests for 3.x on RosieScott Shawcroft
2017-11-02Merge tag 'v1.9.3'Scott Shawcroft
Introduction of ports subdirectory where all ports are moved to The main change in this release is the introduction of a "ports/" subdirectory at the top-level of the repository, and all of the ports are moved here. In the process the "stmhal" port is renamed to "stm32" to better reflect the MCU that it targets. In addition, the STM32 CMSIS and HAL sources are moved to a new submodule called "stm32lib". The bytecode has changed in this release, compared to the previous release, and as a consequence the .mpy version number has increased to version 3. This means that scripts compiled with the previous mpy-cross must be recompiled to work with this new version. There have also been various enhancements and optimisations, such as: check for valid UTF-8 when creating str objects, support for reverse special binary operations like __radd__, full domain checking in the math module, support for floor-division and modulo in the viper emitter, and addition of stack overflow checking when executing a regex. The stm32 port sees improved support for F7 MCUs, addition of a new board B_L475E_IOT01A based on the STM32L475, and support for the Wiznet W5500 chipset along with improved socket behaviour. A detailed list of changes follows. py core: - objstr: startswith, endswith: check arg to be a string - nlrx86,x64: replace #define of defined() with portable macro usage - objtype: handle NotImplemented return from binary special methods - objtype: mp_obj_class_lookup: improve debug logging - map: remove unused new/free functions - make m_malloc_fail() have void return type, since it doesn't return - modstruct: in struct.pack, stop converting if there are no args left - modstruct: check and prevent buffer-read overflow in struct unpacking - modstruct: check and prevent buffer-write overflow in struct packing - nlrthumb: get working again on standard Thumb arch (ie not Thumb2) - objfloat: fix binary ops with incompatible objects - obj: fix comparison of float/complex NaN with itself - objtype: implement fallback for instance inplace special methods - objtuple: properly implement comparison with incompatible types - objstr: add check for valid UTF-8 when making a str from bytes - objlist: properly implement comparison with incompatible types - runtime0.h: move relational ops to the beginning of mp_binary_op_t - runtime0.h: move MP_BINARY_OP_DIVMOD to the end of mp_binary_op_t - objtype: make sure mp_binary_op_method_name has full size again - runtime0.h: put inplace arith ops in front of normal operations - builtinhelp: simplify code slightly by extracting object type - runtime: implement dispatch for "reverse op" special methods - nlrx86: fix building for Android/x86 - builtinhelp: change signature of help text var from pointer to array - runtime.h: change empty mp_warning macro so var-args are non empty - modbuiltins: implement abs() by dispatching to MP_UNARY_OP_ABS - {objfloat,objcomplex}: optimise MP_UNARY_OP_ABS by reusing variables - mpconfig.h: add note that using computed gotos in VM is not C99 - objstr: strip: don't strip "\0" by default - objexcept: prevent infinite recursion when allocating exceptions - stream: remove unnecessary checks for NULL return from vstr_add_len - vstr: raise a RuntimeError if fixed vstr buffer overflows - vm: use lowercase letter at start of exception message - persistentcode: define mp_raw_code_save_file() for any unix target - add config option to print warnings/errors to stderr - objfloat: support raising a negative number to a fractional power - objset: simplify set and frozenset by separating their locals dicts - objset: check that RHS of a binary op is a set/frozenset - objset: include the failed key in a KeyError raised from set.remove - objtype: change type of enum-to-qstr table to uint16_t to save space - objstr: make empty bytes object have a null-terminating byte - mpprint: only check for null string printing when NDEBUG not defined - objtype: clean up unary- and binary-op enum-to-qstr mapping tables - persistentcode: bump .mpy version number to version 3 - bc: update opcode_format_table to match the bytecode - modmath: add full checks for math domain errors - modmath: convert log2 macro into a function - formatfloat: don't print the negative sign of a NaN value - formatfloat: use standard isinf, isnan funcs instead of custom ones - modbuiltins: use existing utf8_get_char helper in builtin ord func - emitnative: implement floor-division and modulo for viper emitter - objtype: use CPython compatible method name for sizeof - objtype: fit qstrs for special methods in byte type - objtype: define all special methods if requested - objtype: introduce MICROPY_PY_ALL_INPLACE_SPECIAL_METHODS extmod: - modubinascii: only include uzlib/tinf.h when it's really needed - modussl_mbedtls: allow to compile with MBEDTLS_DEBUG_C disabled - machine_pinbase: put PinBase singleton in ROM - re1.5: upgrade to v0.8.2, adds hook for stack overflow checking - modure: add stack overflow checking when executing a regex - uos_dupterm: update uos.dupterm() and helper funcs to have index - uos_dupterm: swallow any errors from dupterm closing the stream - vfs: replace VLA in proxy func with small, static sized array - modussl: add finaliser support for ussl objects - modussl_mbedtls: allow to compile with unix coverage build lib: - add new submodule, stm32lib containing STM32 CMSIS and HAL source - embed/abort_: use mp_raise_msg helper function - libm: fix tanhf so that it correctly handles +/- infinity args - libm: remove implementation of log2f, use MP_NEED_LOG2 instead - axtls: update, support for SSL_EAGAIN return code - berkeley-db-1.xx: update, allow to override MINCACHE, DEFPSIZE drivers: - memory/spiflash: change from hard-coded soft SPI to generic SPI - display/ssd1306.py: improve performance of graphics methods - nrf24l01: make nRF24L01 test script more portable - display/ssd1306: implement SSD1306_I2C poweron method - display/ssd1306: make poweron() work the same with SSD1306_SPI - wiznet5k: improve the performance of socket ops with threading - wiznet5k: get low-level W5500 driver working tools: - upip: upgrade to 1.2.2 - pyboard: use repr() when quoting data in error messages - pyboard: update docstring for additional device support tests: - object_new: better messages, check user __new__() method - class_new: add checks for __init__ being called and other improvements - class_new: add another testcase for __new__/__init__ interaction - class_inplace_op: test for inplace op fallback to normal one - run-bench-tests: update locations of executables, now in ports/ - class_reverse_op: test for reverse arith ops special methods - run-tests: skip class_inplace_op for minimal profile - run-tests: fix copy-paste mistake in var name - cpydiff: add cases for locals() discrepancies - extmod: add test for ure regexes leading to infinite recursion - extmod: add test for '-' in character class in regex - run-tests: close device under test using "finally" - net_inet: update tls test to work with CPython and incl new site unix port: - rename modsocket.c to modusocket.c - modusocket: remove #if MICROPY_SOCKET_EXTRA code blocks - enable MICROPY_PY_REVERSE_SPECIAL_METHODS stm32 port: - modmachine: make machine.bootloader() work when MPU is enabled - modmachine: improve support for sleep/deepsleep on F7 MCUs - compute PLL freq table during build instead of at run time - modmachine: for F7 MCU, save power by reducing internal volt reg - boards/pllvalues.py: make script work with both Python 2 and 3 - Makefile: use lib/stm32lib instead of local cmsis and hal files - remove cmsis and hal files, they are now a submodule - Makefile: automatically fetch stm32lib submodule if needed - update to new STM Cube HAL library - fix clock initialisation of L4 MCUs - rename stmhal port directory to stm32 - remove unused usbd_msc.c file - boards: change remaining stm32f4xx_hal_conf.h to unix line ending - boards: change linker scripts to use "K" instead of hex byte size - boards: fix I2C1 pin mapping on NUCLEO_F401RE/F411RE boards - i2c: when scanning for I2C devices only do 1 probe per address - modnwwiznet5k: release the GIL on blocking network operations - boards: add new board B_L475E_IOT01A based on STM32L475 - make-stmconst.py: make sure mpz const data lives in ROM - timer: make pyb.Timer() instances persistent - mpconfigport.h: add configuration for max periphs on L4 series - usbdev: make the USBD callback struct const so it can go in ROM - usbdev: change static function variable to non-static - usbdev: put all CDC state in a struct - usbdev: put all HID state in a struct - usbdev: simplify CDC tx/rx buffer passing - usbdev: simplify HID tx/rx buffer passing - usbdev/core: add state parameter to all callback functions - usbdev: put all state for the USB device driver in a struct - usbdev: simplify pointers to MSC state and block dev operations - usbdev: merge all global USB device state into a single struct - usbdev: make device descriptor callbacks take a state pointer - usbdev: move all the USB device descriptor state into its struct - timer: enable ARPE so that timer freq can be changed smoothly - modnwwiznet5k: get the IP address of an established socket - boards: fix typos in stm32f767_af.csv table - usbd_cdc_interface: don't reset CDC output buf on initialisation - modnwwiznet5k: implement WIZNET5K.isconnected() method - modusocket: make getaddrinfo() work when passed an IP address - modusocket: return OSError(-2) if getaddrinfo fails - mpconfigport.h: add MICROPY_THREAD_YIELD() macro - modnwwiznet5k: add support for W5500 Ethernet chip - modnwwiznet5k: increase SPI bus speed to 42MHz - modnwwiznet5k: implement stream ioctl for the Wiznet driver - mphalport: improve efficiency of mp_hal_stdout_tx_strn_cooked - make uos.dupterm() conform to specs by using extmod version cc3200 port: - enable micropython.kbd_intr() method - use standard implementation of keyboard interrupt esp8266 port: - rename axtls_helpers.c to posix_helpers.c - posix_helpers: set ENOMEM on memory alloc failure - set DEFPSIZE=1024, MINCACHE=3 for "btree" module - esp_mphal: send data in chunks to mp_uos_dupterm_tx_strn - modnetwork: add "bssid" keyword arg to WLAN.connect() method - modules/webrepl_setup: add info about allowed password length zephyr port: - Makefile: revamp "test" target after ports were moved to ports/ - use CONFIG_NET_APP_SETTINGS to setup initial network addresses - switch to interrupt-driven pull-style console pic16bit port: - add definition of SEEK_SET to unistd.h docs: - pyboard/tutorial: add "timeout=0" to UART in pass-through example - more xrefs to "MicroPython port" in glossary - library/network: fix ref to "socket" module (should be "usocket") - machine.Signal: improve style/grammar and add usage example - library: add description of "index" parameter to uos.dupterm() - library/micropython: fix typo in RST formatting - library/framebuf.rst: generalise constructor to all colour formats - btree: describe page caching policy of the underlying implementation - esp8266/tutorial: update neopixel with example of using 4 bbp - library/network: clarify usage of "bssid" arg in connect() method - pyboard/quickref: add info for Switch, RTC, CAN, Accel classes - pyboard/tutorial: update now that yellow LED also supports PWM - esp8266/quickref: add quickref info for RTC class - library: add missing cross-ref links for classes in pyb module - library/network: update docs to state that W5500 is supported - uselect: document one-shot polling mode - usocket: elaborate descriptions - usocket: document inet_ntop(), inet_pton() - library/network: add dhcp_hostname parameter - reference/isr_rules: minor typo correction - ussl: fix module name refs and use "MicroPython port" term - esp8266/general: add section on TLS limitations - usocket: document that settimeout() isn't supported by all ports - ure: add "|" (alternative) to the list of supported operators - reference/isr_rules.rst: add tutorial on use of micropython.schedule() travis: - use --upgrade when pip is installing cpp-coveralls - update build command now that stm32 Wiznet config has changed examples: - hwconfig_console: add .on()/.off() methods all: - convert mp_uint_t to mp_unary_op_t/mp_binary_op_t where appropriate - convert remaining "mp_uint_t n_args" to "size_t n_args" - make new ports/ sub-directory and move all ports there - update Makefiles and others to build with new ports/ dir layout - remove inclusion of internal py header files - use NULL instead of "" when calling mp_raise exception helpers README: - update "Dependencies" section - add explicit section on contributing - add gcc and arm-none-eabi-newlib to list of required components .gitattributes: - remove obsolete entries for stmhal/hal, stmhal/cmsis - add entries for files that will move to ports/ dir
2017-10-27py/objtype: Define all special methods if requested.Paul Sokolovsky
If MICROPY_PY_ALL_SPECIAL_METHODS is defined, actually define all special methods (still subject to gating by e.g. MICROPY_PY_REVERSE_SPECIAL_METHODS). This adds quite a number of qstr's, so should be used sparingly.
2017-10-26tests/net_inet: Update tls test to work with CPython and incl new site.Damien George
CPython only supports the server_hostname keyword arg via the SSLContext object, so use that instead of the top-level ssl.wrap_socket. This allows the test to run on CPython the same as uPy. Also add the "Host:" header to correctly make a GET request (for URLs that are hosted on other servers). This is not strictly needed to test the SSL connection but helps to debug things when printing the response.
2017-10-25tests: Capture stderr output as well.Scott Shawcroft
2017-10-24Merge commit 'f869d6b2e339c04469c6c9ea3fb2fabd7bbb2d8c' into nrf2_mergeScott Shawcroft
This is prep for merging in the NRF5 pull request.
2017-10-18CircuitPython now has struct instead of ustruct (#302)Michael McWethy
Added struct module to shared-bindings and shared-module. removed ustruct
2017-10-11py/emitnative: Implement floor-division and modulo for viper emitter.Damien George
2017-10-10py/formatfloat: Don't print the negative sign of a NaN value.Damien George
NaN may have the sign bit set but it has no meaning, so don't print it out.
2017-10-10py/modmath: Add full checks for math domain errors.Damien George
This patch changes how most of the plain math functions are implemented: there are now two generic math wrapper functions that take a pointer to a math function (like sin, cos) and perform the necessary conversion to and from MicroPython types. This helps to reduce code size. The generic functions can also check for math domain errors in a generic way, by testing if the result is NaN or infinity combined with finite inputs. The result is that, with this patch, all math functions now have full domain error checking (even gamma and lgamma) and code size has decreased for most ports. Code size changes in bytes for those with the math module are: unix x64: -432 unix nanbox: -792 stm32: -88 esp8266: +12 Tests are also added to check domain errors are handled correctly.
2017-10-07tests/run-tests: Close device under test using "finally".Paul Sokolovsky
We want to close communication object even if there were exceptions somewhere in the code. This is important for --device exec:/execpty: which may otherwise leave processing running in the background.
2017-10-05tests/extmod: Add test for '-' in character class in regex.Damien George
2017-10-05py: Clean up unary and binary enum list to keep groups together.Damien George
2 non-bytecode binary ops (NOT_IN and IN_NOT) are moved out of the bytecode group, so this change will change the bytecode format.
2017-10-04py/objstr: Make empty bytes object have a null-terminating byte.Damien George
Because a lot of string processing functions assume there is a null terminating byte, so they can work in an efficient way. Fixes issue #3334.
2017-10-03py/objset: Include the failed key in a KeyError raised from set.remove.Damien George
2017-10-03py/objset: Check that RHS of a binary op is a set/frozenset.Damien George
CPython docs explicitly state that the RHS of a set/frozenset binary op must be a set to prevent user errors. It also preserves commutativity of the ops, eg: "abc" & set() is a TypeError, and so should be set() & "abc". This change actually decreases unix (x64) code by 160 bytes; it increases stm32 by 4 bytes and esp8266 by 28 bytes (but previous patch already introduced a much large saving).
2017-10-03tests/extmod: Add test for ure regexes leading to infinite recursion.Paul Sokolovsky
These now should be caught properly and lead to RuntimeError instead of crash.
2017-09-26py/objfloat: Support raising a negative number to a fractional power.Damien George
This returns a complex number, following CPython behaviour. For ports that don't have complex numbers enabled this will raise a ValueError which gives a fail-safe for scripts that were written assuming complex numbers exist.
2017-09-26py: Add config option to print warnings/errors to stderr.David Lechner
This adds a new configuration option to print runtime warnings and errors to stderr. On Unix, CPython prints warnings and unhandled exceptions to stderr, so the unix port here is configured to use this option. The unix port already printed unhandled exceptions on the main thread to stderr. This patch fixes unhandled exceptions on other threads and warnings (issue #2838) not printing on stderr. Additionally, a couple tests needed to be fixed to handle this new behavior. This is done by also capturing stderr when running tests.
2017-09-25py: Clarify which mp_unary_op_t's may appear in the bytecode.Paul Sokolovsky
Not all can, so we don't need to reserve bytecodes for them, and can use free slots for something else later.
2017-09-21py/vstr: Raise a RuntimeError if fixed vstr buffer overflows.Damien George
Current users of fixed vstr buffers (building file paths) assume that there is no overflow and do not check for overflow after building the vstr. This has the potential to lead to NULL pointer dereferences (when vstr_null_terminated_str returns NULL because it can't allocate RAM for the terminating byte) and stat'ing and loading invalid path names (due to the path being truncated). The safest and simplest thing to do in these cases is just raise an exception if a write goes beyond the end of a fixed vstr buffer, which is what this patch does. It also simplifies the vstr code.
2017-09-21py/objexcept: Prevent infinite recursion when allocating exceptions.Damien George
The aim of this patch is to rewrite the functions that create exception instances (mp_obj_exception_make_new and mp_obj_new_exception_msg_varg) so that they do not call any functions that may raise an exception. Otherwise it's possible to create infinite recursion with an exception being raised while trying to create an exception object. The two main things that are done to accomplish this are: 1. Change mp_obj_new_exception_msg_varg to just format the string, then call mp_obj_exception_make_new to actually create the exception object. 2. In mp_obj_exception_make_new and mp_obj_new_exception_msg_varg try to allocate all memory first using functions that don't raise exceptions If any of the memory allocations fail (return NULL) then degrade gracefully by trying other options for memory allocation, eg using the emergency exception buffer. 3. Use a custom printer backend to conservatively format strings: if it can't allocate memory then it just truncates the string. As part of this rewrite, raising an exception without a message, like KeyError(123), will now use the emergency buffer to store the arg and traceback data if there is no heap memory available. Memory use with this patch is unchanged. Code size is increased by: bare-arm: +136 minimal x86: +124 unix x64: +72 unix nanbox: +96 stm32: +88 esp8266: +92 cc3200: +80
2017-09-19py/objstr: strip: Don't strip "\0" by default.Paul Sokolovsky
An issue was due to incorrectly taking size of default strip characters set.
2017-09-18py/modbuiltins: Implement abs() by dispatching to MP_UNARY_OP_ABS.Paul Sokolovsky
This allows user classes to implement __abs__ special method, and saves code size (104 bytes for x86_64), even though during refactor, an issue was fixed and few optimizations were made: * abs() of minimum (negative) small int value is calculated properly. * objint_longlong and objint_mpz avoid allocating new object is the argument is already non-negative.
2017-09-16tests/cpydiff: Add cases for locals() discrepancies.Paul Sokolovsky
MicroPython doesn't maintain local symbolic environment, so any feature depending on it won't work as expected.
2017-09-10tests/run-tests: Fix copy-paste mistake in var name.Paul Sokolovsky
2017-09-10tests/run-tests: Skip class_inplace_op for minimal profile.Paul Sokolovsky
Don't assume that MICROPY_PY_ALL_SPECIAL_METHODS is defined, as required for inplace special methods. Fixes Zephyr tests.
2017-09-10tests/class_reverse_op: Test for reverse arith ops special methods.Paul Sokolovsky
This test should be run only if support for reverse ops is enabled, so the corresponding feature_check is added to run-tests.
2017-09-08tests/run-bench-tests: Update locations of executables, now in ports/.Damien George
2017-09-08py/runtime0.h: Put inplace arith ops in front of normal operations.Paul Sokolovsky
This is to allow to place reverse ops immediately after normal ops, so they can be tested as one range (which is optimization for reverse ops introduction in the next patch).
2017-09-07py/runtime0.h: Move MP_BINARY_OP_DIVMOD to the end of mp_binary_op_t.Paul Sokolovsky
It starts a dichotomy of mp_binary_op_t values which can't appear in the bytecode. Another reason to move it is to VALUES of OP_* and OP_INPLACE_* nicely adjacent. This also will be needed for OP_REVERSE_*, to be soon introduced.
2017-09-07py/runtime0.h: Move relational ops to the beginning of mp_binary_op_t.Paul Sokolovsky
This is to allow to encode arithmetic operations more efficiently, in preparation to introduction of __rOP__ method support.
2017-09-07py/objlist: Properly implement comparison with incompatible types.Paul Sokolovsky
Should raise TypeError, unless it's (in)equality comparison.
2017-09-06py/objstr: Add check for valid UTF-8 when making a str from bytes.tll
This patch adds a function utf8_check() to check for a valid UTF-8 encoded string, and calls it when constructing a str from raw bytes. The feature is selectable at compile time via MICROPY_PY_BUILTINS_STR_UNICODE_CHECK and is enabled if unicode is enabled. It costs about 110 bytes on Thumb-2, 150 bytes on Xtensa and 170 bytes on x86-64.
2017-09-06all: Update Makefiles and others to build with new ports/ dir layout.Damien George
Also renames "stmhal" to "stm32" in documentation and everywhere else.
2017-09-06py/objtuple: Properly implement comparison with incompatible types.Paul Sokolovsky
Should raise TypeError, unless it's (in)equality comparison.
2017-09-04tests/class_inplace_op: Test for inplace op fallback to normal one.Paul Sokolovsky
2017-09-04py/obj: Fix comparison of float/complex NaN with itself.Damien George
IEEE floating point is specified such that a comparison of NaN with itself returns false, and Python respects these semantics. This patch makes uPy also have these semantics. The fix has a minor impact on the speed of the object-equality fast-path, but that seems to be unavoidable and it's much more important to have correct behaviour (especially in this case where the wrong answer for nan==nan is silently returned).
2017-09-02py/objfloat: Fix binary ops with incompatible objects.Paul Sokolovsky
These are now returned as "operation not supported" instead of raising TypeError. In particular, this fixes equality for float vs incompatible types, which now properly results in False instead of exception. This also paves the road to support reverse operation (e.g. __radd__) with float objects. This is achieved by introducing mp_obj_get_float_maybe(), similar to existing mp_obj_get_int_maybe().
2017-09-01py/modstruct: Check and prevent buffer-write overflow in struct packing.Damien George
Prior to this patch, the size of the buffer given to pack_into() was checked for being too small by using the count of the arguments, not their actual size. For example, a format spec of '4I' would only check that there was 4 bytes available, not 16; and 'I' would check for 1 byte, not 4. The pack() function is ok because its buffer is created to be exactly the correct size. The fix in this patch calculates the total size of the format spec at the start of pack_into() and verifies that the buffer is large enough. This adds some computational overhead, to iterate through the whole format spec. The alternative is to check during the packing, but that requires extra code to handle alignment, and the check is anyway not needed for pack(). So to maintain minimal code size the check is done using struct_calcsize.
2017-09-01py/modstruct: Check and prevent buffer-read overflow in struct unpackingDamien George
Prior to this patch, the size of the buffer given to unpack/unpack_from was checked for being too small by using the count of the arguments, not their actual size. For example, a format spec of '4I' would only check that there was 4 bytes available, not 16; and 'I' would check for 1 byte, not 4. This bug is fixed in this patch by calculating the total size of the format spec at the start of the unpacking function. This function anyway needs to calculate the number of items at the start, so calculating the total size can be done at the same time.
2017-09-01py/modstruct: In struct.pack, stop converting if there are no args left.Damien George
This patch makes a repeat counter behave the same as repeating the typecode, when there are not enough args. For example: struct.pack('2I', 1) now behave the same as struct.pack('II', 1).
2017-09-01tests/class_new: Add another testcase for __new__/__init__ interaction.Paul Sokolovsky
Similar to the existing testcase, but test that returning both value of native type and instance of another user class from __new__ lead to __init__ not being called, for better coverage.
2017-08-30tests/class_new: Add checks for __init__ being called and other improvements.Paul Sokolovsky
2017-08-30tests/object_new: Better messages, check user __new__() method.Paul Sokolovsky
Make messages more verbose and easier to follow and check that user class' __new__() is not called by object.__new__(user_class).
2017-08-30py/objtype: Handle NotImplemented return from binary special methods.Paul Sokolovsky
NotImplemented means "try other fallbacks (like calling __rop__ instead of __op__) and if nothing works, raise TypeError". As MicroPython doesn't implement any fallbacks, signal to raise TypeError right away.
2017-08-29py/objstr: startswith, endswith: Check arg to be a string.Paul Sokolovsky
Otherwise, it will silently get incorrect result on other values types, including CPython tuple form like "foo.png".endswith(("png", "jpg")) (which MicroPython doesn't support for unbloatedness).
2017-08-25Initial merge of micropython v1.9.2 into circuitpython 2.0.0 (in ↵Dan Halbert
development) master. cpx build compiles and loads and works in repl; test suite not run yet esp8266 not tested yet
2017-08-25atmel-samd: Introduce a nvm module for non-volatile byte-level memory ↵Scott Shawcroft
access. (#203) * atmel-samd: Introduce a nvm module for non-volatile byte-level memory access. This allows for persisting small configuration values even when the file system is read-only from CircuitPython. Fixes #160 * Review feedback: * Add tests. * Fix non-zero index. * Fix len()
2017-08-20py/stream: seek: Consistently handle negative offset for SEEK_SET.Paul Sokolovsky
Per POSIX, this is EINVAL, so raises OSError(EINVAL).