Cython Changelog

0.29.29 (2022-05-16)

Features added

  • Avoid acquiring the GIL at the end of nogil functions. This change was backported in order to avoid generating wrong C code that would trigger C compiler warnings with tracing support enabled. Backport by Oleksandr Pavlyk. (Github issue #4637)

Bugs fixed

  • Function definitions in finally: clauses were not correctly generated. Patch by David Woods. (Github issue #4651)

  • A case where C-API functions could be called with a live exception set was fixed. Patch by Jakub Kulík. (Github issue #4722)

  • Pickles can now be exchanged again with those generated from Cython 3.0 modules. (Github issue #4680)

  • Cython now correctly generates Python methods for both the provided regular and reversed special numeric methods of extension types. Patch by David Woods. (Github issue #4750)

  • Calling unbound extension type methods without arguments could raise an IndexError instead of a TypeError. Patch by David Woods. (Github issue #4779)

  • Calling unbound .__contains__() super class methods on some builtin base types could trigger an infinite recusion. Patch by David Woods. (Github issue #4785)

  • The C union type in pure Python mode mishandled some field names. Patch by Jordan Brière. (Github issue #4727)

  • Allow users to overwrite the C macro _USE_MATH_DEFINES. Patch by Yuriy Chernyshov. (Github issue #4690)

  • Improved compatibility with CPython 3.10/11. Patches by Thomas Caswell, David Woods. (Github issues #4609, #4667, #4721, #4730, #4777)

  • Docstrings of descriptors are now provided in PyPy 7.3.9. Patch by Matti Picus. (Github issue #4701)

0.29.28 (2022-02-17)

Bugs fixed

  • Due to backwards incompatible changes in CPython 3.11a4, the feature flags CYTHON_FAST_THREAD_STATE and CYTHON_USE_EXC_INFO_STACK are now disabled in Python 3.11 and later. They are enabled again in Cython 3.0. Patch by David Woods. (Github issue #4610)

  • A C compiler warning in older PyPy versions was resolved. Patch by Matti Picus. (Github issue #4236)

0.29.27 (2022-01-28)

Features added

  • The cythonize command has a new option -M to generate .dep dependency files for the compilation unit. This can be used by external build tools to track these dependencies. Patch by Evgeni Burovski. (Github issue #1214)

Bugs fixed

  • Compilation failures on PyPy were resolved. Patches by Matti Picus. (Github issues #4509, #4517)

  • Calls to range() with more than three arguments did not fail. Original patch by Max Bachmann. (Github issue #4550)

  • Some C compiler warnings about missing type struct initialisers in Py3.10 were resolved.

  • Cython no longer warns about using OpenMP 3.0 features since they are now considered generally available.

0.29.26 (2021-12-16)

Bugs fixed

  • An incompatibility with CPython 3.11.0a3 was resolved. (Github issue #4499)

  • The in operator failed on literal lists with starred expressions. Patch by Arvind Natarajan. (Github issue #3938)

  • A C compiler warning in PyPy about a missing struct field initialisation was resolved.

0.29.25 (2021-12-06)

Bugs fixed

  • Several incompatibilities with CPython 3.11 were resolved. Patches by David Woods, Victor Stinner, Thomas Caswell. (Github issues #4411, #4414, #4415, #4416, #4420, #4428, #4473, #4479, #4480)

  • Some C compiler warnings were resolved. Patches by Lisandro Dalcin and others. (Github issue #4439)

  • C++ std::move() should only be used automatically in MSVC versions that support it. Patch by Max Bachmann. (Github issue #4191)

  • The Py_hash_t type failed to accept arbitrary “index” values. (Github issue #2752)

  • Avoid copying unaligned 16-bit values since some platforms require them to be aligned. Use memcpy() instead to let the C compiler decide how to do it. (Github issue #4343)

  • Cython crashed on invalid truthiness tests on C++ types without operator bool. Patch by David Woods. (Github issue #4348)

  • The declaration of PyUnicode_CompareWithASCIIString() in cpython.unicode was incorrect. Patch by Max Bachmann. (Github issue #4344)

0.29.24 (2021-07-14)

Bugs fixed

  • Inline functions in pxd files that used memory views could lead to invalid C code if the module that imported from them does not use memory views. Patch by David Woods. (Github issue #1415)

  • Several declarations in libcpp.string were added and corrected. Patch by Janek Bevendorff. (Github issue #4268)

  • Pickling unbound Cython compiled methods failed. Patch by Pierre Glaser. (Github issue #2972)

  • The tracing code was adapted to work with CPython 3.10.

  • The optimised in operator failed on unicode strings in Py3.9 and later that were constructed from an external wchar_t source. Also, related C compiler warnings about deprecated C-API usage were resolved. (Github issue #3925)

  • Some compiler crashes were resolved. Patch by David Woods. (Github issues #4214, #2811)

  • An incorrect warning about ‘unused’ generator expressions was removed. (GIthub issue #1699)

  • The attributes gen.gi_frame and coro.cr_frame of Cython compiled generators and coroutines now return an actual frame object for introspection, instead of None. (Github issue #2306)

0.29.23 (2021-04-14)

Bugs fixed

  • Some problems with Python 3.10 were resolved. Patches by Victor Stinner and David Woods. (Github issues #4046, #4100)

  • An incorrect “optimisation” was removed that allowed changes to a keyword dict to leak into keyword arguments passed into a function. Patch by Peng Weikang. (Github issue #3227)

  • Multiplied str constants could end up as bytes constants with language_level=2. Patch by Alphadelta14 and David Woods. (Github issue #3951)

  • PY_SSIZE_T_CLEAN does not get defined any more if it is already defined. Patch by Andrew Jones. (Github issue #4104)

0.29.22 (2021-02-20)

Features added

  • Some declarations were added to the provided pxd includes. Patches by Zackery Spytz and John Kirkham. (Github issues #3811, #3882, #3899, #3901)

Bugs fixed

  • A crash when calling certain functions in Py3.9 and later was resolved. (Github issue #3917)

  • const memory views of structs failed to compile. (Github issue #2251)

  • const template declarations could not be nested. Patch by Ashwin Srinath. (Github issue #1355)

  • The declarations in the cpython.pycapsule module were missing their const modifiers and generated incorrect C code. Patch by Warren Weckesser. (Github issue #3964)

  • Casts to memory views failed for fused dtypes. Patch by David Woods. (Github issue #3881)

  • repr() was assumed to return str instead of unicode with language_level=3. (Github issue #3736)

  • Calling cpdef functions from cimported modules crashed the compiler. Patch by David Woods. (Github issue #4000)

  • Cython no longer validates the ABI size of the NumPy classes it compiled against. See the discussion in

  • A C compiler warning about enum value casting was resolved in GCC. (Github issue #2749)

  • Coverage reporting in the annotated HTML file failed in Py3.9. Patch by Nick Pope. (Github issue #3865)

  • The embedding code now reports Python errors as exit status.

  • Long type declarations could lead to (harmless) random changes in the C file when used in auto-generated Python wrappers or pickled classes.

Other changes

  • Variables defined as cpdef now generate a warning since this is currently useless and thus does not do what users would expect. Patch by David Woods. (Github issue #3959)

0.29.21 (2020-07-09)

Bugs fixed

  • Fix a regression in 0.29.20 where __div__ failed to be found in extension types. (Github issue #3688)

  • Fix a regression in 0.29.20 where a call inside of a finally clause could fail to compile. Patch by David Woods. (Github issue #3712)

  • Zero-sized buffers could fail to validate as C/Fortran-contiguous. Patch by Clemens Hofreither. (Github issue #2093)

  • exec() did not allow recent Python syntax features in Py3.8+ due to (Github issue #3695)

  • Binding staticmethods of Cython functions were not behaving like Python methods in Py3. Patch by Jeroen Demeyer and Michał Górny. (Github issue #3106)

  • Pythran calls to NumPy methods no longer generate useless method lookup code.

  • The PyUnicode_GET_LENGTH() macro was missing from the cpython.* declarations. Patch by Thomas Caswell. (Github issue #3692)

  • The deprecated PyUnicode_*() C-API functions are no longer used, except for Unicode strings that contain lone surrogates. Unicode strings that contain non-BMP characters or surrogate pairs now generate different C code on 16-bit Python 2.x Unicode deployments (such as MS-Windows). Generating the C code on Python 3.x is recommended in this case. Original patches by Inada Naoki and Victor Stinner. (Github issues #3677, #3721, #3697)

  • Some template parameters were missing from the C++ std::unordered_map declaration. Patch by will. (Github issue #3685)

  • Several internal code generation issues regarding temporary variables were resolved. (Github issue #3708)

0.29.20 (2020-06-10)

Bugs fixed

  • Nested try-except statements with multiple return statements could crash due to incorrect deletion of the except as target variable. (Github issue #3666)

  • The @classmethod decorator no longer rejects unknown input from other decorators. Patch by David Woods. (Github issue #3660)

  • Fused types could leak into unrelated usages. Patch by David Woods. (Github issue #3642)

  • Now uses Py_SET_SIZE() and Py_SET_REFCNT() in Py3.9+ to avoid low-level write access to these object fields. Patch by Victor Stinner. (Github issue #3639)

  • The built-in abs() function could lead to undefined behaviour when used on the negative-most value of a signed C integer type. Patch by Serge Guelton. (Github issue #1911)

  • Usages of sizeof() and typeid() on uninitialised variables no longer produce a warning. Patch by Celelibi. (Github issue #3575)

  • The C++ typeid() function was allowed in C mode. Patch by Celelibi. (Github issue #3637)

  • The error position reported for errors found in f-strings was misleading. (Github issue #3674)

  • The new c_api_binop_methods directive was added for forward compatibility, but can only be set to True (the current default value). It can be disabled in Cython 3.0.

0.29.19 (2020-05-20)

Bugs fixed

  • A typo in Windows specific code in 0.29.18 was fixed that broke “libc.math”. (Github issue #3622)

  • A platform specific test failure in 0.29.18 was fixed. Patch by smutch. (Github issue #3620)

0.29.18 (2020-05-18)

Bugs fixed

  • Exception position reporting could run into race conditions on threaded code. It now uses function-local variables again.

  • Error handling early in the module init code could lead to a crash.

  • Error handling in cython.array creation was improved to avoid calling C-API functions with an error held.

  • A memory corruption was fixed when garbage collection was triggered during calls to PyType_Ready() of extension type subclasses. (Github issue #3603)

  • Memory view slicing generated unused error handling code which could negatively impact the C compiler optimisations for parallel OpenMP code etc. Also, it is now helped by static branch hints. (Github issue #2987)

  • Cython’s built-in OpenMP functions were not translated inside of call arguments. Original patch by Celelibi and David Woods. (Github issue #3594)

  • Complex buffer item types of structs of arrays could fail to validate. Patch by Leo and smutch. (Github issue #1407)

  • Decorators were not allowed on nested async def functions. (Github issue #1462)

  • C-tuples could use invalid C struct casting. Patch by MegaIng. (Github issue #3038)

  • Optimised %d string formatting into f-strings failed on float values. (Github issue #3092)

  • Optimised aligned string formatting (%05s, %-5s) failed. (Github issue #3476)

  • When importing the old Cython build_ext integration with distutils, the additional command line arguments leaked into the regular command. Patch by Kamekameha. (Github issue #2209)

  • When using the CYTHON_NO_PYINIT_EXPORT option in C++, the module init function was not declared as extern "C". (Github issue #3414)

  • Three missing timedelta access macros were added in cpython.datetime.

  • The signature of the NumPy C-API function PyArray_SearchSorted() was fixed. Patch by Brock Mendel. (Github issue #3606)

0.29.17 (2020-04-26)

Features added

  • std::move() is now available from libcpp.utility. Patch by Omer Ozarslan. (Github issue #2169)

  • The @cython.binding decorator is available in Python code. (Github issue #3505)

Bugs fixed

  • Creating an empty unicode slice with large bounds could crash. Patch by Sam Sneddon. (Github issue #3531)

  • Decoding an empty bytes/char* slice with large bounds could crash. Patch by Sam Sneddon. (Github issue #3534)

  • Re-importing a Cython extension no longer raises the error “__reduce_cython__ not found”. (Github issue #3545)

  • Unused C-tuples could generate incorrect code in 0.29.16. Patch by Kirk Meyer. (Github issue #3543)

  • Creating a fused function attached it to the garbage collector before it was fully initialised, thus risking crashes in rare failure cases. Original patch by achernomorov. (Github issue #3215)

  • Temporary buffer indexing variables were not released and could show up in C compiler warnings, e.g. in generators. Patch by David Woods. (Github issues #3430, #3522)

  • The compilation cache in cython.inline("…") failed to take the language level into account. Patch by will-ca. (Github issue #3419)

  • The deprecated PyUnicode_GET_SIZE() function is no longer used in Py3.

0.29.16 (2020-03-24)

Bugs fixed

  • Temporary internal variables in nested prange loops could leak into other threads. Patch by Frank Schlimbach. (Github issue #3348)

  • Default arguments on fused functions could crash. Patch by David Woods. (Github issue #3370)

  • C-tuples declared in .pxd files could generate incomplete C code. Patch by Kirk Meyer. (Github issue #1427)

  • Fused functions were not always detected and optimised as Cython implemented functions. Patch by David Woods. (Github issue #3384)

  • Valid Python object concatenation of (iterable) strings to non-strings could fail with an exception. Patch by David Woods. (Github issue #3433)

  • Using C functions as temporary values lead to invalid C code. Original patch by David Woods. (Github issue #3418)

  • Fix an unhandled C++ exception in comparisons. Patch by David Woods. (Github issue #3361)

  • Fix deprecated import of “imp” module. Patch by Matti Picus. (Github issue #3350)

  • Fix compatibility with Pythran 0.9.6 and later. Patch by Serge Guelton. (Github issue #3308)

  • The _Py_PyAtExit() function in cpython.pylifecycle was misdeclared. Patch by Zackery Spytz. (Github issue #3382)

  • Several missing declarations in cpython.* were added. Patches by Zackery Spytz. (Github issue #3452, #3421, #3411, #3402)

  • A declaration for libc.math.fpclassify() was added. Patch by Zackery Spytz. (Github issue #2514)

  • Avoid “undeclared” warning about automatically generated pickle methods. Patch by David Woods. (Github issue #3353)

  • Avoid C compiler warning about unreachable code in prange().

  • Some C compiler warnings in PyPy were resolved. Patch by Matti Picus. (Github issue #3437)

0.29.15 (2020-02-06)

Bugs fixed

  • Crash when returning a temporary Python object from an async-def function. (Github issue #3337)

  • Crash when using **kwargs in generators. Patch by David Woods. (Github issue #3265)

  • Double reference free in __class__ cell handling for super() calls. (Github issue #3246)

  • Compile error when using *args as Python class bases. (Github issue #3338)

  • Import failure in IPython 7.11. (Github issue #3297)

  • Fixed C name collision in the auto-pickle code. Patch by ThePrez. (Github issue #3238)

  • Deprecated import failed in Python 3.9. (Github issue #3266)

0.29.14 (2019-11-01)

Bugs fixed

  • The generated code failed to initialise the tp_print slot in CPython 3.8. Patches by Pablo Galindo and Orivej Desh. (Github issues #3171, #3201)

  • ? for bool was missing from the supported NumPy dtypes. Patch by Max Klein. (Github issue #2675)

  • await was not allowed inside of f-strings. Patch by Dmitro Getz. (Github issue #2877)

  • Coverage analysis failed for projects where the code resides in separate source sub-directories. Patch by Antonio Valentino. (Github issue #1985)

  • An incorrect compiler warning was fixed in automatic C++ string conversions. Patch by Gerion Entrup. (Github issue #3108)

  • Error reports in the Jupyter notebook showed unhelpful stack traces. Patch by Matthew Edwards (Github issue #3196).

  • Python.h is now also included explicitly from public header files. (Github issue #3133).

  • Distutils builds with --parallel did not work when using Cython’s deprecated build_ext command. Patch by Alphadelta14 (Github issue #3187).

Other changes

  • The PyMemoryView_*() C-API is available in cpython.memoryview. Patch by Nathan Manville. (Github issue #2541)

0.29.13 (2019-07-26)

Bugs fixed

  • A reference leak for None was fixed when converting a memoryview to a Python object. (Github issue #3023)

  • The declaration of PyGILState_STATE in cpython.pystate was unusable. Patch by Kirill Smelkov. (Github issue #2997)

Other changes

  • The declarations in posix.mman were extended. Patches by Kirill Smelkov. (Github issues #2893, #2894, #3012)

0.29.12 (2019-07-07)

Bugs fixed

  • Fix compile error in CPython 3.8b2 regarding the PyCode_New() signature. (Github issue #3031)

  • Fix a C compiler warning about a missing int downcast. (Github issue #3028)

  • Fix reported error positions of undefined builtins and constants. Patch by Orivej Desh. (Github issue #3030)

  • A 32 bit issue in the Pythran support was resolved. Patch by Serge Guelton. (Github issue #3032)

0.29.11 (2019-06-30)

Bugs fixed

  • Fix compile error in CPython 3.8b2 regarding the PyCode_New() signature. Patch by Nick Coghlan. (Github issue #3009)

  • Invalid C code generated for lambda functions in cdef methods. Patch by Josh Tobin. (Github issue #2967)

  • Support slice handling in newer Pythran versions. Patch by Serge Guelton. (Github issue #2989)

  • A reference leak in power-of-2 calculation was fixed. Patch by Sebastian Berg. (Github issue #3022)

  • The search order for include files was changed. Previously it was include_directories, Cython/Includes, sys.path. Now it is include_directories, sys.path, Cython/Includes. This was done to allow third-party *.pxd files to override the ones in Cython. Original patch by Matti Picus. (Github issue #2905)

  • Setting language_level=2 in a file did not work if language_level=3 was enabled globally before. Patch by Jeroen Demeyer. (Github issue #2791)

0.29.10 (2019-06-02)

Bugs fixed

  • Fix compile errors in CPython 3.8b1 due to the new “tp_vectorcall” slots. (Github issue #2976)

0.29.9 (2019-05-29)

Bugs fixed

  • Fix a crash regression in 0.29.8 when creating code objects fails.

  • Remove an incorrect cast when using true-division in C++ operations. (Github issue #1950)

0.29.8 (2019-05-28)

Bugs fixed

  • C compile errors with CPython 3.8 were resolved. Patch by Marcel Plch. (Github issue #2938)

  • Python tuple constants that compare equal but have different item types could incorrectly be merged into a single constant. (Github issue #2919)

  • Non-ASCII characters in unprefixed strings could crash the compiler when used with language level 3str.

  • Starred expressions in %-formatting tuples could fail to compile for unicode strings. (Github issue #2939)

  • Passing Python class references through cython.inline() was broken. (Github issue #2936)

0.29.7 (2019-04-14)

Bugs fixed

  • Crash when the shared Cython config module gets unloaded and another Cython module reports an exceptions. Cython now makes sure it keeps an owned reference to the module. (Github issue #2885)

  • Resolved a C89 compilation problem when enabling the fast-gil sharing feature.

  • Coverage reporting did not include the signature line of cdef functions. (Github issue #1461)

  • Casting a GIL-requiring function into a nogil function now issues a warning. (Github issue #2879)

  • Generators and coroutines were missing their return type annotation. (Github issue #2884)

0.29.6 (2019-02-27)

Bugs fixed

  • Fix a crash when accessing the __kwdefaults__ special attribute of fused functions. (Github issue #1470)

  • Fix the parsing of buffer format strings that contain numeric sizes, which could lead to incorrect input rejections. (Github issue #2845)

  • Avoid a C #pragma in old gcc versions that was only added in GCC 4.6. Patch by Michael Anselmi. (Github issue #2838)

  • Auto-encoding of Unicode strings to UTF-8 C/C++ strings failed in Python 3, even though the default encoding there is UTF-8. (Github issue #2819)

0.29.5 (2019-02-09)

Bugs fixed

  • Crash when defining a Python subclass of an extension type and repeatedly calling a cpdef method on it. (Github issue #2823)

  • Compiler crash when prange() loops appear inside of with-statements. (Github issue #2780)

  • Some C compiler warnings were resolved. Patches by Christoph Gohlke. (Github issues #2815, #2816, #2817, #2822)

  • Python conversion of C++ enums failed in 0.29. Patch by Orivej Desh. (Github issue #2767)

0.29.4 (2019-02-01)

Bugs fixed

  • Division of numeric constants by a runtime value of 0 could fail to raise a ZeroDivisionError. (Github issue #2820)

0.29.3 (2019-01-19)

Bugs fixed

  • Some C code for memoryviews was generated in a non-deterministic order. Patch by Martijn van Steenbergen. (Github issue #2779)

  • C89 compatibility was accidentally lost since 0.28. Patches by gastineau and true-pasky. (Github issues #2778, #2801)

  • A C compiler cast warning was resolved. Patch by Michael Buesch. (Github issue #2774)

  • An compilation failure with complex numbers under MSVC++ was resolved. (Github issue #2797)

  • Coverage reporting could fail when modules were moved around after the build. Patch by Wenjun Si. (Github issue #2776)

0.29.2 (2018-12-14)

Bugs fixed

  • The code generated for deduplicated constants leaked some references. (Github issue #2750)

  • The declaration of sigismember() in libc.signal was corrected. (Github issue #2756)

  • Crashes in compiler and test runner were fixed. (Github issue #2736, #2755)

  • A C compiler warning about an invalid safety check was resolved. (Github issue #2731)

0.29.1 (2018-11-24)

Bugs fixed

  • Extensions compiled with MinGW-64 under Windows could misinterpret integer objects larger than 15 bit and return incorrect results. (Github issue #2670)

  • Cython no longer requires the source to be writable when copying its data into a memory view slice. Patch by Andrey Paramonov. (Github issue #2644)

  • Line tracing of try-statements generated invalid C code. (Github issue #2274)

  • When using the warn.undeclared directive, Cython’s own code generated warnings that are now fixed. Patch by Nicolas Pauss. (Github issue #2685)

  • Cython’s memoryviews no longer require strides for setting the shape field but only the PyBUF_ND flag to be set. Patch by John Kirkham. (Github issue #2716)

  • Some C compiler warnings about unused memoryview code were fixed. Patch by Ho Cheuk Ting. (Github issue #2588)

  • A C compiler warning about implicit signed/unsigned conversion was fixed. (Github issue #2729)

  • Assignments to C++ references returned by operator[] could fail to compile. (Github issue #2671)

  • The power operator and the support for NumPy math functions were fixed in Pythran expressions. Patch by Serge Guelton. (Github issues #2702, #2709)

  • Signatures with memory view arguments now show the expected type when embedded in docstrings. Patch by Matthew Chan and Benjamin Weigel. (Github issue #2634)

  • Some from ... cimport ... constructs were not correctly considered when searching modified dependencies in cythonize() to decide whether to recompile a module. Patch by Kryštof Pilnáček. (Github issue #2638)

  • A struct field type in the cpython.array declarations was corrected. Patch by John Kirkham. (Github issue #2712)

0.29 (2018-10-14)

Features added

  • PEP-489 multi-phase module initialisation has been enabled again. Module reloads in other subinterpreters raise an exception to prevent corruption of the static module state.

  • A set of mypy compatible PEP-484 declarations were added for Cython’s C data types to integrate with static analysers in typed Python code. They are available in the Cython/Shadow.pyi module and describe the types in the special cython module that can be used for typing in Python code. Original patch by Julian Gethmann. (Github issue #1965)

  • Memoryviews are supported in PEP-484/526 style type declarations. (Github issue #2529)

  • @cython.nogil is supported as a C-function decorator in Python code. (Github issue #2557)

  • Raising exceptions from nogil code will automatically acquire the GIL, instead of requiring an explicit with gil block.

  • C++ functions can now be declared as potentially raising both C++ and Python exceptions, so that Cython can handle both correctly. (Github issue #2615)

  • cython.inline() supports a direct language_level keyword argument that was previously only available via a directive.

  • A new language level name 3str was added that mostly corresponds to language level 3, but keeps unprefixed string literals as type ‘str’ in both Py2 and Py3, and the builtin ‘str’ type unchanged. This will become the default in the next Cython release and is meant to help user code a) transition more easily to this new default and b) migrate to Python 3 source code semantics without making support for Python 2.x difficult.

  • In CPython 3.6 and later, looking up globals in the module dict is almost as fast as looking up C globals. (Github issue #2313)

  • For a Python subclass of an extension type, repeated method calls to non-overridden cpdef methods can avoid the attribute lookup in Py3.6+, which makes them 4x faster. (Github issue #2313)

  • (In-)equality comparisons of objects to integer literals are faster. (Github issue #2188)

  • Some internal and 1-argument method calls are faster.

  • Modules that cimport many external extension types from other Cython modules execute less import requests during module initialisation.

  • Constant tuples and slices are deduplicated and only created once per module. (Github issue #2292)

  • The coverage plugin considers more C file extensions such as .cc and .cxx. (Github issue #2266)

  • The cythonize command accepts compile time variable values (as set by DEF) through the new -E option. Patch by Jerome Kieffer. (Github issue #2315)

  • pyximport can import from namespace packages. Patch by Prakhar Goel. (Github issue #2294)

  • Some missing numpy and CPython C-API declarations were added. Patch by John Kirkham. (Github issues #2523, #2520, #2537)

  • Declarations for the pylifecycle C-API functions were added in a new .pxd file cpython.pylifecycle.

  • The Pythran support was updated to work with the latest Pythran 0.8.7. Original patch by Adrien Guinet. (Github issue #2600)

  • %a is included in the string formatting types that are optimised into f-strings. In this case, it is also automatically mapped to %r in Python 2.x.

  • New C macro CYTHON_HEX_VERSION to access Cython’s version in the same style as PY_VERSION_HEX.

  • Constants in libc.math are now declared as const to simplify their handling.

  • An additional check_size clause was added to the ctypedef class name specification to allow suppressing warnings when importing modules with backwards-compatible PyTypeObject size changes. Patch by Matti Picus. (Github issue #2627)

Bugs fixed

  • The exception handling in generators and coroutines under CPython 3.7 was adapted to the newly introduced exception stack. Users of Cython 0.28 who want to support Python 3.7 are encouraged to upgrade to 0.29 to avoid potentially incorrect error reporting and tracebacks. (Github issue #1958)

  • Crash when importing a module under Stackless Python that was built for CPython. Patch by Anselm Kruis. (Github issue #2534)

  • 2-value slicing of typed sequences failed if the start or stop index was None. Patch by Christian Gibson. (Github issue #2508)

  • Multiplied string literals lost their factor when they are part of another constant expression (e.g. ‘x’ * 10 + ‘y’ => ‘xy’).

  • String formatting with the ‘%’ operator didn’t call the special __rmod__() method if the right side is a string subclass that implements it. (Python issue 28598)

  • The directive language_level=3 did not apply to the first token in the source file. (Github issue #2230)

  • Overriding cpdef methods did not work in Python subclasses with slots. Note that this can have a performance impact on calls from Cython code. (Github issue #1771)

  • Fix declarations of builtin or C types using strings in pure python mode. (Github issue #2046)

  • Generator expressions and lambdas failed to compile in @cfunc functions. (Github issue #459)

  • Global names with const types were not excluded from star-import assignments which could lead to invalid C code. (Github issue #2621)

  • Several internal function signatures were fixed that lead to warnings in gcc-8. (Github issue #2363)

  • The numpy helper functions set_array_base() and get_array_base() were adapted to the current numpy C-API recommendations. Patch by Matti Picus. (Github issue #2528)

  • Some NumPy related code was updated to avoid deprecated API usage. Original patch by jbrockmendel. (Github issue #2559)

  • Several C++ STL declarations were extended and corrected. Patch by Valentin Valls. (Github issue #2207)

  • C lines of the module init function were unconditionally not reported in exception stack traces. Patch by Jeroen Demeyer. (Github issue #2492)

  • When PEP-489 support is enabled, reloading the module overwrote any static module state. It now raises an exception instead, given that reloading is not actually supported.

  • Object-returning, C++ exception throwing functions were not checking that the return value was non-null. Original patch by Matt Wozniski (Github Issue #2603)

  • The source file encoding detection could get confused if the c_string_encoding directive appeared within the first two lines. (Github issue #2632)

  • Cython generated modules no longer emit a warning during import when the size of the NumPy array type is larger than what was found at compile time. Instead, this is assumed to be a backwards compatible change on NumPy side.

Other changes

  • Cython now emits a warning when no language_level (2, 3 or ‘3str’) is set explicitly, neither as a cythonize() option nor as a compiler directive. This is meant to prepare the transition of the default language level from currently Py2 to Py3, since that is what most new users will expect these days. The future default will, however, not enforce unicode literals, because this has proven a major obstacle in the support for both Python 2.x and 3.x. The next major release is intended to make this change, so that it will parse all code that does not request a specific language level as Python 3 code, but with str literals. The language level 2 will continue to be supported for an indefinite time.

  • The documentation was restructured, cleaned up and examples are now tested. The NumPy tutorial was also rewritten to simplify the running example. Contributed by Gabriel de Marmiesse. (Github issue #2245)

  • Cython compiles less of its own modules at build time to reduce the installed package size to about half of its previous size. This makes the compiler slightly slower, by about 5-7%.

0.28.6 (2018-11-01)

Bugs fixed

  • Extensions compiled with MinGW-64 under Windows could misinterpret integer objects larger than 15 bit and return incorrect results. (Github issue #2670)

  • Multiplied string literals lost their factor when they are part of another constant expression (e.g. ‘x’ * 10 + ‘y’ => ‘xy’).

0.28.5 (2018-08-03)

Bugs fixed

  • The discouraged usage of GCC’s attribute optimize("Os") was replaced by the similar attribute cold to reduce the code impact of the module init functions. (Github issue #2494)

  • A reference leak in Py2.x was fixed when comparing str to unicode for equality.

0.28.4 (2018-07-08)

Bugs fixed

  • Reallowing tp_clear() in a subtype of an @no_gc_clear extension type generated an invalid C function call to the (non-existent) base type implementation. (Github issue #2309)

  • Exception catching based on a non-literal (runtime) tuple could fail to match the exception. (Github issue #2425)

  • Compile fix for CPython 3.7.0a2. (Github issue #2477)

0.28.3 (2018-05-27)

Bugs fixed

  • Set iteration was broken in non-CPython since 0.28.

  • UnicodeEncodeError in Py2 when %s formatting is optimised for unicode strings. (Github issue #2276)

  • Work around a crash bug in g++ 4.4.x by disabling the size reduction setting of the module init function in this version. (Github issue #2235)

  • Crash when exceptions occur early during module initialisation. (Github issue #2199)

0.28.2 (2018-04-13)

Features added

  • abs() is faster for Python long objects.

  • The C++11 methods front() and end() were added to the declaration of libcpp.string. Patch by Alex Huszagh. (Github issue #2123)

  • The C++11 methods reserve() and bucket_count() are declared for libcpp.unordered_map. Patch by Valentin Valls. (Github issue #2168)

Bugs fixed

  • The copy of a read-only memoryview was considered read-only as well, whereas a common reason to copy a read-only view is to make it writable. The result of the copying is now a writable buffer by default. (Github issue #2134)

  • The switch statement generation failed to apply recursively to the body of converted if-statements.

  • NULL was sometimes rejected as exception return value when the returned type is a fused pointer type. Patch by Callie LeFave. (Github issue #2177)

  • Fixed compatibility with PyPy 5.11. Patch by Matti Picus. (Github issue #2165)

Other changes

  • The NumPy tutorial was rewritten to use memoryviews instead of the older buffer declaration syntax. Contributed by Gabriel de Marmiesse. (Github issue #2162)

0.28.1 (2018-03-18)

Bugs fixed

  • PyFrozenSet_New() was accidentally used in PyPy where it is missing from the C-API.

  • Assignment between some C++ templated types were incorrectly rejected when the templates mix const with ctypedef. (Github issue #2148)

  • Undeclared C++ no-args constructors in subclasses could make the compilation fail if the base class constructor was declared without nogil. (Github issue #2157)

  • Bytes %-formatting inferred basestring (bytes or unicode) as result type in some cases where bytes would have been safe to infer. (Github issue #2153)

  • None was accidentally disallowed as typed return value of dict.pop(). (Github issue #2152)

0.28 (2018-03-13)

Features added

  • Cdef classes can now multiply inherit from ordinary Python classes. (The primary base must still be a c class, possibly object, and the other bases must not be cdef classes.)

  • Type inference is now supported for Pythran compiled NumPy expressions. Patch by Nils Braun. (Github issue #1954)

  • The const modifier can be applied to memoryview declarations to allow read-only buffers as input. (Github issues #1605, #1869)

  • C code in the docstring of a cdef extern block is copied verbatimly into the generated file. Patch by Jeroen Demeyer. (Github issue #1915)

  • When compiling with gcc, the module init function is now tuned for small code size instead of whatever compile flags were provided externally. Cython now also disables some code intensive optimisations in that function to further reduce the code size. (Github issue #2102)

  • Decorating an async coroutine with @cython.iterable_coroutine changes its type at compile time to make it iterable. While this is not strictly in line with PEP-492, it improves the interoperability with old-style coroutines that use yield from instead of await.

  • The IPython magic has preliminary support for JupyterLab. (Github issue #1775)

  • The new TSS C-API in CPython 3.7 is supported and has been backported. Patch by Naotoshi Seo. (Github issue #1932)

  • Cython knows the new Py_tss_t type defined in PEP-539 and automatically initialises variables declared with that type to Py_tss_NEEDS_INIT, a value which cannot be used outside of static assignments.

  • The set methods .remove() and .discard() are optimised. Patch by Antoine Pitrou. (Github issue #2042)

  • dict.pop() is optimised. Original patch by Antoine Pitrou. (Github issue #2047)

  • Iteration over sets and frozensets is optimised. (Github issue #2048)

  • Safe integer loops (< range(2^30)) are automatically optimised into C loops.

  • alist.extend([a,b,c]) is optimised into sequential list.append() calls for short literal sequences.

  • Calls to builtin methods that are not specifically optimised into C-API calls now use a cache that avoids repeated lookups of the underlying C function. (Github issue #2054)

  • Single argument function calls can avoid the argument tuple creation in some cases.

  • Some redundant extension type checks are avoided.

  • Formatting C enum values in f-strings is faster, as well as some other special cases.

  • String formatting with the ‘%’ operator is optimised into f-strings in simple cases.

  • Subscripting (item access) is faster in some cases.

  • Some bytearray operations have been optimised similar to bytes.

  • Some PEP-484/526 container type declarations are now considered for loop optimisations.

  • Indexing into memoryview slices with view[i][j] is now optimised into view[i, j].

  • Python compatible cython.* types can now be mixed with type declarations in Cython syntax.

  • Name lookups in the module and in classes are faster.

  • Python attribute lookups on extension types without instance dict are faster.

  • Some missing signals were added to libc/signal.pxd. Patch by Jeroen Demeyer. (Github issue #1914)

  • The warning about repeated extern declarations is now visible by default. (Github issue #1874)

  • The exception handling of the function types used by CPython’s type slot functions was corrected to match the de-facto standard behaviour, so that code that uses them directly benefits from automatic and correct exception propagation. Patch by Jeroen Demeyer. (Github issue #1980)

  • Defining the macro CYTHON_NO_PYINIT_EXPORT will prevent the module init function from being exported as symbol, e.g. when linking modules statically in an embedding setup. Patch by AraHaan. (Github issue #1944)

Bugs fixed

  • If a module name is explicitly provided for an Extension() that is compiled via cythonize(), it was previously ignored and replaced by the source file name. It can now be used to override the target module name, e.g. for compiling prefixed accelerator modules from Python files. (Github issue #2038)

  • The arguments of the num_threads parameter of parallel sections were not sufficiently validated and could lead to invalid C code. (Github issue #1957)

  • Catching exceptions with a non-trivial exception pattern could call into CPython with a live exception set. This triggered incorrect behaviour and crashes, especially in CPython 3.7.

  • The signature of the special __richcmp__() method was corrected to recognise the type of the first argument as self. It was previously treated as plain object, but CPython actually guarantees that it always has the correct type. Note: this can change the semantics of user code that previously relied on self being untyped.

  • Some Python 3 exceptions were not recognised as builtins when running Cython under Python 2.

  • Some async helper functions were not defined in the generated C code when compiling simple async code. (Github issue #2075)

  • Line tracing did not include generators and coroutines. (Github issue #1949)

  • C++ declarations for unordered_map were corrected. Patch by Michael Schatzow. (Github issue #1484)

  • Iterator declarations in C++ deque and vector were corrected. Patch by Alex Huszagh. (Github issue #1870)

  • The const modifiers in the C++ string declarations were corrected, together with the coercion behaviour of string literals into C++ strings. (Github issue #2132)

  • Some declaration types in libc.limits were corrected. Patch by Jeroen Demeyer. (Github issue #2016)

  • was not accepted on Python classes with an @cython.cclass decorator. (Github issue #2040)

  • Cython no longer creates useless and incorrect PyInstanceMethod wrappers for methods in Python 3. Patch by Jeroen Demeyer. (Github issue #2105)

  • The builtin bytearray type could not be used as base type of cdef classes. (Github issue #2106)

Other changes

0.27.3 (2017-11-03)

Bugs fixed

  • String forward references to extension types like @cython.locals(x="ExtType") failed to find the named type. (Github issue #1962)

  • NumPy slicing generated incorrect results when compiled with Pythran. Original patch by Serge Guelton (Github issue #1946).

  • Fix “undefined reference” linker error for generators on Windows in Py3.3-3.5. (Github issue #1968)

  • Adapt to recent C-API change of PyThreadState in CPython 3.7.

  • Fix signature of PyWeakref_GetObject() API declaration. Patch by Jeroen Demeyer (Github issue #1975).

0.27.2 (2017-10-22)

Bugs fixed

  • Comprehensions could incorrectly be optimised away when they appeared in boolean test contexts. (Github issue #1920)

  • The special methods __eq__, __lt__ etc. in extension types did not type their first argument as the type of the class but object. (Github issue #1935)

  • Crash on first lookup of “cline_in_traceback” option during exception handling. (Github issue #1907)

  • Some nested module level comprehensions failed to compile. (Github issue #1906)

  • Compiler crash on some complex type declarations in pure mode. (Github issue #1908)

  • std::unordered_map.erase() was declared with an incorrect void return type in libcpp.unordered_map. (Github issue #1484)

  • Invalid use of C++ fallthrough attribute before C++11 and similar issue in clang. (Github issue #1930)

  • Compiler crash on misnamed properties. (Github issue #1905)

0.27.1 (2017-10-01)

Features added

  • The Jupyter magic has a new debug option --verbose that shows details about the distutils invocation. Patch by Boris Filippov (Github issue #1881).

Bugs fixed

  • Py3 list comprehensions in class bodies resulted in invalid C code. (Github issue #1889)

  • Modules built for later CPython 3.5.x versions failed to import in 3.5.0/3.5.1. (Github issue #1880)

  • Deallocating fused types functions and methods kept their GC tracking enabled, which could potentially lead to recursive deallocation attempts.

  • Crash when compiling in C++ mode with old setuptools versions. (Github issue #1879)

  • C++ object arguments for the constructor of Cython implemented C++ are now passed by reference and not by value to allow for non-copyable arguments, such as unique_ptr.

  • API-exported C++ classes with Python object members failed to compile. (Github issue #1866)

  • Some issues with the new relaxed exception value handling were resolved.

  • Python classes as annotation types could prevent compilation. (Github issue #1887)

  • Cython annotation types in Python files could lead to import failures with a “cython undefined” error. Recognised types are now turned into strings.

  • Coverage analysis could fail to report on extension modules on some platforms.

  • Annotations could be parsed (and rejected) as types even with annotation_typing=False.

Other changes

  • PEP 489 support has been disabled by default to counter incompatibilities with import setups that try to reload or reinitialise modules.

0.27 (2017-09-23)

Features added

  • Extension module initialisation follows PEP 489 in CPython 3.5+, which resolves several differences with regard to normal Python modules. This makes the global names __file__ and __path__ correctly available to module level code and improves the support for module-level relative imports. (Github issues #1715, #1753, #1035)

  • Asynchronous generators (PEP 525) and asynchronous comprehensions (PEP 530) have been implemented. Note that async generators require finalisation support in order to allow for asynchronous operations during cleanup, which is only available in CPython 3.6+. All other functionality has been backported as usual.

  • Variable annotations are now parsed according to PEP 526. Cython types (e.g. are evaluated as C type declarations and everything else as Python types. This can be disabled with the directive annotation_typing=False. Note that most complex PEP-484 style annotations are currently ignored. This will change in future releases. (Github issue #1850)

  • Extension types (also in pure Python mode) can implement the normal special methods __eq__, __lt__ etc. for comparisons instead of the low-level __richcmp__ method. (Github issue #690)

  • New decorator @cython.exceptval(x=None, check=False) that makes the signature declarations except x, except? x and except * available to pure Python code. Original patch by Antonio Cuni. (Github issue #1653)

  • Signature annotations are now included in the signature docstring generated by the embedsignature directive. Patch by Lisandro Dalcin (Github issue #1781).

  • The gdb support for Python code ( was updated to the latest version in CPython 3.7 (git rev 5fe59f8).

  • The compiler tries to find a usable exception return value for cdef functions with except * if the returned type allows it. Note that this feature is subject to safety limitations, so it is still better to provide an explicit declaration.

  • C functions can be assigned to function pointers with a compatible exception declaration, not only with exact matches. A side-effect is that certain compatible signature overrides are now allowed and some more mismatches of exception signatures are now detected and rejected as errors that were not detected before.

  • The IPython/Jupyter magic integration has a new option %%cython --pgo for profile guided optimisation. It compiles the cell with PGO settings for the C compiler, executes it to generate a runtime profile, and then compiles it again using that profile for C compiler optimisation. Currently only tested with gcc.

  • len(memoryview) can be used in nogil sections to get the size of the first dimension of a memory view (shape[0]). (Github issue #1733)

  • C++ classes can now contain (properly refcounted) Python objects.

  • NumPy dtype subarrays are now accessible through the C-API. Patch by Gerald Dalley (Github issue #245).

  • Resolves several issues with PyPy and uses faster async slots in PyPy3. Patch by Ronan Lamy (Github issues #1871, #1878).

Bugs fixed

  • Extension types that were cimported from other Cython modules could disagree about the order of fused cdef methods in their call table. This could lead to wrong methods being called and potentially also crashes. The fix required changes to the ordering of fused methods in the call table, which may break existing compiled modules that call fused cdef methods across module boundaries, if these methods were implemented in a different order than they were declared in the corresponding .pxd file. (Github issue #1873)

  • The exception state handling in generators and coroutines could lead to exceptions in the caller being lost if an exception was raised and handled inside of the coroutine when yielding. (Github issue #1731)

  • Loops over range(enum) were not converted into C for-loops. Note that it is still recommended to use an explicit cast to a C integer type in this case.

  • Error positions of names (e.g. variables) were incorrectly reported after the name and not at the beginning of the name.

  • Compile time DEF assignments were evaluated even when they occur inside of falsy IF blocks. (Github issue #1796)

  • Disabling the line tracing from a trace function could fail. Original patch by Dmitry Trofimov. (Github issue #1769)

  • Several issues with the Pythran integration were resolved.

  • abs(signed int) now returns a signed rather than unsigned int. (Github issue #1837)

  • Reading frame.f_locals of a Cython function (e.g. from a debugger or profiler could modify the module globals. (Github issue #1836)

  • Buffer type mismatches in the NumPy buffer support could leak a reference to the buffer owner.

  • Using the “is_f_contig” and “is_c_contig” memoryview methods together could leave one of them undeclared. (Github issue #1872)

  • Compilation failed if the for-in-range loop target was not a variable but a more complex expression, e.g. an item assignment. (Github issue #1831)

  • Compile time evaluations of (partially) constant f-strings could show incorrect results.

  • Escape sequences in raw f-strings (fr'...') were resolved instead of passing them through as expected.

  • Some ref-counting issues in buffer error handling have been resolved.

Other changes

  • Type declarations in signature annotations are now parsed according to PEP 484 typing. Only Cython types (e.g. and Python builtin types are currently considered as type declarations. Everything else is ignored, but this will change in a future Cython release. (Github issue #1672)

  • The directive annotation_typing is now True by default, which enables parsing type declarations from annotations.

  • This release no longer supports Python 3.2.

0.26.1 (2017-08-29)

Features added

Bugs fixed

  • cython.view.array was missing .__len__().

  • Extension types with a .pxd override for their __releasebuffer__ slot (e.g. as provided by Cython for the Python array.array type) could leak a reference to the buffer owner on release, thus not freeing the memory. (Github issue #1638)

  • Auto-decoding failed in 0.26 for strings inside of C++ containers. (Github issue #1790)

  • Compile error when inheriting from C++ container types. (Github issue #1788)

  • Invalid C code in generators (declaration after code). (Github issue #1801)

  • Arithmetic operations on const integer variables could generate invalid code. (Github issue #1798)

  • Local variables with names of special Python methods failed to compile inside of closures. (Github issue #1797)

  • Problem with indirect Emacs buffers in cython-mode. Patch by Martin Albrecht (Github issue #1743).

  • Extension types named result or PickleError generated invalid unpickling code. Patch by Jason Madden (Github issue #1786).

  • Bazel integration failed to compile .py files. Patch by Guro Bokum (Github issue #1784).

  • Some include directories and dependencies were referenced with their absolute paths in the generated files despite lying within the project directory.

  • Failure to compile in Py3.7 due to a modified signature of _PyCFunctionFast()

0.26 (2017-07-19)

Features added

  • Pythran can be used as a backend for evaluating NumPy array expressions. Patch by Adrien Guinet (Github issue #1607).

  • cdef classes now support pickling by default when possible. This can be disabled with the auto_pickle directive.

  • Speed up comparisons of strings if their hash value is available. Patch by Claudio Freire (Github issue #1571).

  • Support pyximport from zip files. Patch by Sergei Lebedev (Github issue #1485).

  • IPython magic now respects the __all__ variable and ignores names with leading-underscore (like import * does). Patch by Syrtis Major (Github issue #1625).

  • abs() is optimised for C complex numbers. Patch by da-woods (Github issue #1648).

  • The display of C lines in Cython tracebacks can now be enabled at runtime via import cython_runtime; cython_runtime.cline_in_traceback=True. The default has been changed to False.

  • The overhead of calling fused types generic functions was reduced.

  • “cdef extern” include files are now also searched relative to the current file. Patch by Jeroen Demeyer (Github issue #1654).

  • Optional optimization for re-aquiring the GIL, controlled by the fast_gil directive.

Bugs fixed

  • Item lookup/assignment with a unicode character as index that is typed (explicitly or implicitly) as Py_UCS4 or Py_UNICODE used the integer value instead of the Unicode string value. Code that relied on the previous behaviour now triggers a warning that can be disabled by applying an explicit cast. (Github issue #1602)

  • f-string processing was adapted to changes in PEP 498 and CPython 3.6.

  • Invalid C code when decoding from UTF-16(LE/BE) byte strings. (Github issue #1696)

  • Unicode escapes in ‘ur’ raw-unicode strings were not resolved in Py2 code. Original patch by Aaron Gallagher (Github issue #1594).

  • File paths of code objects are now relative. Original patch by Jelmer Vernooij (Github issue #1565).

  • Decorators of cdef class methods could be executed twice. Patch by Jeroen Demeyer (Github issue #1724).

  • Dict iteration using the Py2 iter* methods failed in PyPy3. Patch by Armin Rigo (Github issue #1631).

  • Several warnings in the generated code are now suppressed.

Other changes

  • The unraisable_tracebacks option now defaults to True.

  • Coercion of C++ containers to Python is no longer automatic on attribute access (Github issue #1521).

  • Access to Python attributes of cimported modules without the corresponding import is now a compile-time (rather than runtime) error.

  • Do not use special dll linkage for “cdef public” functions. Patch by Jeroen Demeyer (Github issue #1687).

  • cdef/cpdef methods must match their declarations. See Github Issue #1732. This is now a warning and will be an error in future releases.

0.25.2 (2016-12-08)

Bugs fixed

  • Fixes several issues with C++ template deduction.

  • Fixes a issue with bound method type inference (Github issue #551).

  • Fixes a bug with cascaded tuple assignment (Github issue #1523).

  • Fixed or silenced many Clang warnings.

  • Fixes bug with powers of pure real complex numbers (Github issue #1538).

0.25.1 (2016-10-26)

Bugs fixed

  • Fixes a bug with isinstance(o, Exception) (Github issue #1496).

  • Fixes bug with cython.view.array missing utility code in some cases (Github issue #1502).

Other changes

  • The distutils extension Cython.Distutils.build_ext has been reverted, temporarily, to be old_build_ext to give projects time to migrate. The new build_ext is available as new_build_ext.

0.25 (2016-10-25)

Features added

  • def/cpdef methods of cdef classes benefit from Cython’s internal function implementation, which enables introspection and line profiling for them. Implementation sponsored by Turbostream (

  • Calls to Python functions are faster, following the recent “FastCall” optimisations that Victor Stinner implemented for CPython 3.6. See and related issues.

  • The new METH_FASTCALL calling convention for PyCFunctions is supported in CPython 3.6. See

  • Initial support for using Cython modules in Pyston. Patch by Boxiang Sun.

  • Dynamic Python attributes are allowed on cdef classes if an attribute cdef dict __dict__ is declared in the class. Patch by empyrical.

  • Cython implemented C++ classes can make direct calls to base class methods. Patch by empyrical.

  • C++ classes can now have typedef members. STL containers updated with value_type.

  • New directive cython.no_gc to fully disable GC for a cdef class. Patch by Claudio Freire.

  • Buffer variables are no longer excluded from locals(). Patch by da-woods.

  • Building f-strings is faster, especially when formatting C integers.

  • for-loop iteration over “std::string”.

  • libc/math.pxd provides e and pi as alias constants to simplify usage as a drop-in replacement for Python’s math module.

  • Speed up cython.inline().

  • Binary lshift operations with small constant Python integers are faster.

  • Some integer operations on Python long objects are faster in Python 2.7.

  • Support for the C++ typeid operator.

  • Support for bazel using a the pyx_library rule in //Tools:rules.bzl.

Significant Bugs fixed

  • Division of complex numbers avoids overflow by using Smith’s method.

  • Some function signatures in libc.math and numpy.pxd were incorrect. Patch by Michael Seifert.

Other changes

  • The “%%cython” IPython/jupyter magic now defaults to the language level of the current jupyter kernel. The language level can be set explicitly with “%%cython -2” or “%%cython -3”.

  • The distutils extension Cython.Distutils.build_ext has now been updated to use cythonize which properly handles dependencies. The old extension can still be found in Cython.Distutils.old_build_ext and is now deprecated.

  • directive_defaults is no longer available in Cython.Compiler.Options, use get_directive_defaults() instead.

0.24.1 (2016-07-15)

Bugs fixed

  • IPython cell magic was lacking a good way to enable Python 3 code semantics. It can now be used as “%%cython -3”.

  • Follow a recent change in PEP 492 and CPython 3.5.2 that now requires the __aiter__() method of asynchronous iterators to be a simple def method instead of an async def method.

  • Coroutines and generators were lacking the __module__ special attribute.

  • C++ std::complex values failed to auto-convert from and to Python complex objects.

  • Namespaced C++ types could not be used as memory view types due to lack of name mangling. Patch by Ivan Smirnov.

  • Assignments between identical C++ types that were declared with differently typedefed template types could fail.

  • Rebuilds could fail to evaluate dependency timestamps in C++ mode. Patch by Ian Henriksen.

  • Macros defined in the distutils compiler option do not require values anymore. Patch by Ian Henriksen.

  • Minor fixes for MSVC, Cygwin and PyPy.

0.24 (2016-04-04)

Features added

  • PEP 498: Literal String Formatting (f-strings). Original patch by Jelle Zijlstra.

  • PEP 515: Underscores as visual separators in number literals.

  • Parser was adapted to some minor syntax changes in Py3.6, e.g.

  • The embedded C code comments that show the original source code can be discarded with the new directive emit_code_comments=False.

  • Cpdef enums are now first-class iterable, callable types in Python.

  • Ctuples can now be declared in pure Python code.

  • Posix declarations for DLL loading and stdio extensions were added. Patch by Lars Buitinck.

  • The Py2-only builtins unicode(), xrange(), reduce() and long are now also available in compile time DEF expressions when compiling with Py3.

  • Exception type tests have slightly lower overhead. This fixes ticket 868.

  • @property syntax fully supported in cdef classes, old syntax deprecated.

  • C++ classes can now be declared with default template parameters.

Bugs fixed

  • C++ exceptions raised by overloaded C++ operators were not always handled. Patch by Ian Henriksen.

  • C string literals were previously always stored as non-const global variables in the module. They are now stored as global constants when possible, and otherwise as non-const C string literals in the generated code that uses them. This improves compatibility with strict C compiler options and prevents non-const strings literals with the same content from being incorrectly merged.

  • Compile time evaluated str expressions (DEF) now behave in a more useful way by turning into Unicode strings when compiling under Python 3. This allows using them as intermediate values in expressions. Previously, they always evaluated to bytes objects.

  • isinf() declarations in libc/math.pxd and numpy/math.pxd now reflect the actual tristate int return value instead of using bint.

  • Literal assignments to ctuples avoid Python tuple round-trips in some more corner cases.

  • Iteration over dict(...).items() failed to get optimised when dict arguments included keyword arguments.

  • cProfile now correctly profiles cpdef functions and methods.

0.23.5 (2016-03-26)

  • Compile errors and warnings in integer type conversion code. This fixes ticket 877. Patches by Christian Neukirchen, Nikolaus Rath, Ian Henriksen.

  • Reference leak when “*args” argument was reassigned in closures.

  • Truth-testing Unicode strings could waste time and memory in Py3.3+.

  • Return values of async functions could be ignored and replaced by None.

  • Compiler crash in CPython 3.6.

  • Fix prange() to behave identically to range(). The end condition was miscalculated when the range was not exactly divisible by the step.

  • Optimised all(genexpr)/any(genexpr) calls could warn about unused code. This fixes ticket 876.

0.23.4 (2015-10-10)

Bugs fixed

  • Memory leak when calling Python functions in PyPy.

  • Compilation problem with MSVC in C99-ish mode.

  • Warning about unused values in a helper macro.

0.23.3 (2015-09-29)

Bugs fixed

  • Invalid C code for some builtin methods. This fixes ticket 856 again.

  • Incorrect C code in helper functions for PyLong conversion and string decoding. This fixes ticket 863, ticket 864 and ticket 865. Original patch by Nikolaus Rath.

  • Large folded or inserted integer constants could use too small C integer types and thus trigger a value wrap-around.

Other changes

  • The coroutine and generator types of Cython now also register directly with the Coroutine and Generator ABCs in the backports_abc module if it can be imported. This fixes ticket 870.

0.23.2 (2015-09-11)

Bugs fixed

  • Compiler crash when analysing some optimised expressions.

  • Coverage plugin was adapted to 4.0 beta 2.

  • C++ destructor calls could fail when ‘&’ operator is overwritten.

  • Incorrect C literal generation for large integers in compile-time evaluated DEF expressions and constant folded expressions.

  • Byte string constants could end up as Unicode strings when originating from compile-time evaluated DEF expressions.

  • Invalid C code when caching known builtin methods. This fixes ticket 860.

  • ino_t in posix.types was not declared as unsigned.

  • Declarations in libcpp/memory.pxd were missing operator!(). Patch by Leo Razoumov.

  • Static cdef methods can now be declared in .pxd files.

0.23.1 (2015-08-22)

Bugs fixed

  • Invalid C code for generators. This fixes ticket 858.

  • Invalid C code for some builtin methods. This fixes ticket 856.

  • Invalid C code for unused local buffer variables. This fixes ticket 154.

  • Test failures on 32bit systems. This fixes ticket 857.

  • Code that uses from xyz import * and global C struct/union/array variables could fail to compile due to missing helper functions. This fixes ticket 851.

  • Misnamed PEP 492 coroutine property cr_yieldfrom renamed to cr_await to match CPython.

  • Missing deallocation code for C++ object attributes in certain extension class hierarchies.

  • Crash when async coroutine was not awaited.

  • Compiler crash on yield in signature annotations and default argument values. Both are forbidden now.

  • Compiler crash on certain constructs in finally clauses.

  • Cython failed to build when CPython’s pgen is installed.

0.23 (2015-08-08)

Features added

  • PEP 492 (async/await) was implemented.

  • PEP 448 (Additional Unpacking Generalizations) was implemented.

  • Support for 4.0+ can be enabled by adding the plugin “Cython.Coverage” to the “.coveragerc” config file.

  • Annotated HTML source pages can integrate (XML) coverage reports.

  • Tracing is supported in nogil functions/sections and module init code.

  • When generators are used in a Cython module and the module imports the modules “inspect” and/or “asyncio”, Cython enables interoperability by patching these modules during the import to recognise Cython’s internal generator and coroutine types. This can be disabled by C compiling the module with “-D CYTHON_PATCH_ASYNCIO=0” or “-D CYTHON_PATCH_INSPECT=0”

  • When generators or coroutines are used in a Cython module, their types are registered with the Generator and Coroutine ABCs in the collections or stdlib module at import time to enable interoperability with code that needs to detect and process Python generators/coroutines. These ABCs were added in CPython 3.5 and are available for older Python versions through the backports_abc module on PyPI. See

  • Adding/subtracting/dividing/modulus and equality comparisons with constant Python floats and small integers are faster.

  • Binary and/or/xor/rshift operations with small constant Python integers are faster.

  • When called on generator expressions, the builtins all(), any(), dict(), list(), set(), sorted() and unicode.join() avoid the generator iteration overhead by inlining a part of their functionality into the for-loop.

  • Keyword argument dicts are no longer copied on function entry when they are not being used or only passed through to other function calls (e.g. in wrapper functions).

  • The PyTypeObject declaration in cpython.object was extended.

  • The builtin type type is now declared as PyTypeObject in source, allowing for extern functions taking type parameters to have the correct C signatures. Note that this might break code that uses type just for passing around Python types in typed variables. Removing the type declaration provides a backwards compatible fix.

  • wraparound() and boundscheck() are available as no-ops in pure Python mode.

  • Const iterators were added to the provided C++ STL declarations.

  • Smart pointers were added to the provided C++ STL declarations. Patch by Daniel Filonik.

  • NULL is allowed as default argument when embedding signatures. This fixes ticket 843.

  • When compiling with --embed, the internal module name is changed to __main__ to allow arbitrary program names, including those that would be invalid for modules. Note that this prevents reuse of the generated C code as an importable module.

  • External C++ classes that overload the assignment operator can be used. Patch by Ian Henriksen.

  • Support operator bool() for C++ classes so they can be used in if statements.

Bugs fixed

  • Calling “yield from” from Python on a Cython generator that returned a value triggered a crash in CPython. This is now being worked around. See

  • Language level 3 did not enable true division (a.k.a. float division) for integer operands.

  • Functions with fused argument types that included a generic ‘object’ fallback could end up using that fallback also for other explicitly listed object types.

  • Relative cimports could accidentally fall back to trying an absolute cimport on failure.

  • The result of calling a C struct constructor no longer requires an intermediate assignment when coercing to a Python dict.

  • C++ exception declarations with mapping functions could fail to compile when pre-declared in .pxd files.

  • cpdef void methods are now permitted.

  • abs(cint) could fail to compile in MSVC and used sub-optimal code in C++. Patch by David Vierra, original patch by Michael Enßlin.

  • Buffer index calculations using index variables with small C integer types could overflow for large buffer sizes. Original patch by David Vierra.

  • C unions use a saner way to coerce from and to Python dicts.

  • When compiling a module foo.pyx, the directories in sys.path are no longer searched when looking for foo.pxd. Patch by Jeroen Demeyer.

  • Memory leaks in the embedding main function were fixed. Original patch by Michael Enßlin.

  • Some complex Python expressions could fail to compile inside of finally clauses.

  • Unprefixed ‘str’ literals were not supported as C varargs arguments.

  • Fixed type errors in conversion enum types to/from Python. Note that this imposes stricter correctness requirements on enum declarations.

Other changes

  • Changed mangling scheme in header files generated by cdef api declarations.

  • Installation under CPython 3.3+ no longer requires a pass of the 2to3 tool. This also makes it possible to run Cython in Python 3.3+ from a source checkout without installing it first. Patch by Petr Viktorin.

  • (in Tools/) was extended and renamed to (to make it importable) and now works with and requires Jedi 0.9. Patch by Tzer-jen Wei.

0.22.1 (2015-06-20)

Bugs fixed

  • Crash when returning values on generator termination.

  • In some cases, exceptions raised during internal isinstance() checks were not propagated.

  • Runtime reported file paths of source files (e.g for profiling and tracing) are now relative to the build root directory instead of the main source file.

  • Tracing exception handling code could enter the trace function with an active exception set.

  • The internal generator function type was not shared across modules.

  • Comparisons of (inferred) ctuples failed to compile.

  • Closures inside of cdef functions returning void failed to compile.

  • Using const C++ references in intermediate parts of longer expressions could fail to compile.

  • C++ exception declarations with mapping functions could fail to compile when pre-declared in .pxd files.

  • C++ compilation could fail with an ambiguity error in recent MacOS-X Xcode versions.

  • C compilation could fail in pypy3.

  • Fixed a memory leak in the compiler when compiling multiple modules.

  • When compiling multiple modules, external library dependencies could leak into later compiler runs. Fix by Jeroen Demeyer. This fixes ticket 845.

0.22 (2015-02-11)

Features added

  • C functions can coerce to Python functions, which allows passing them around as callable objects.

  • C arrays can be assigned by value and auto-coerce from Python iterables and to Python lists (and tuples).

  • Extern C functions can now be declared as cpdef to export them to the module’s Python namespace. Extern C functions in pxd files export their values to their own module, iff it exists.

  • Anonymous C tuple types can be declared as (ctype1, ctype2, …).

  • PEP 479: turn accidental StopIteration exceptions that exit generators into a RuntimeError, activated with future import “generator_stop”.

  • Looping over reversed(range()) is optimised in the same way as range(). Patch by Favian Contreras.

Bugs fixed

  • Mismatching ‘except’ declarations on signatures in .pxd and .pyx files failed to produce a compile error.

  • Failure to find any files for the path pattern(s) passed into cythonize() is now an error to more easily detect accidental typos.

  • The logaddexp family of functions in numpy.math now has correct declarations.

  • In Py2.6/7 and Py3.2, simple Cython memory views could accidentally be interpreted as non-contiguous by CPython, which could trigger a CPython bug when copying data from them, thus leading to data corruption. See CPython issues 12834 and 23349.

Other changes

  • Preliminary support for defining the Cython language with a formal grammar. To try parsing your files against this grammar, use the –formal_grammar directive. Experimental.

  • _ is no longer considered a cacheable builtin as it could interfere with gettext.

  • Cythonize-computed metadata now cached in the generated C files.

  • Several corrections and extensions in numpy, cpython, and libcpp pxd files.

0.21.2 (2014-12-27)

Bugs fixed

  • Crash when assigning a C value to both a Python and C target at the same time.

  • Automatic coercion from C++ strings to str generated incomplete code that failed to compile.

  • Declaring a constructor in a C++ child class erroneously required a default constructor declaration in the super class.

  • resize_smart() in cpython.array was broken.

  • Functions in libcpp.cast are now declared as nogil.

  • Some missing C-API declarations were added.

  • Py3 main code in embedding program code was lacking casts.

  • Exception related to distutils “Distribution” class type in pyximport under latest CPython 2.7 and 3.4 releases when setuptools is being imported later.

0.21.1 (2014-10-18)

Features added

  • New cythonize option -a to generate the annotated HTML source view.

  • Missing C-API declarations in cpython.unicode were added.

  • Passing language='c++' into cythonize() globally enables C++ mode for all modules that were not passed as Extension objects (i.e. only source files and file patterns).

  • Py_hash_t is a known type (used in CPython for hash values).

  • PySlice_*() C-API functions are available from the cpython.slice module.

  • Allow arrays of C++ classes.

Bugs fixed

  • Reference leak for non-simple Python expressions in boolean and/or expressions.

  • To fix a name collision and to reflect availability on host platforms, standard C declarations [ clock(), time(), struct tm and tm* functions ] were moved from posix/time.pxd to a new libc/time.pxd. Patch by Charles Blake.

  • Rerunning unmodified modules in IPython’s cython support failed. Patch by Matthias Bussonier.

  • Casting C++ std::string to Python byte strings failed when auto-decoding was enabled.

  • Fatal exceptions in global module init code could lead to crashes if the already created module was used later on (e.g. through a stale reference in sys.modules or elsewhere).

  • script was not installed on MS-Windows.

Other changes

  • Compilation no longer fails hard when unknown compilation options are passed. Instead, it raises a warning and ignores them (as it did silently before 0.21). This will be changed back to an error in a future release.

0.21 (2014-09-10)

Features added

  • C (cdef) functions allow inner Python functions.

  • Enums can now be declared as cpdef to export their values to the module’s Python namespace. Cpdef enums in pxd files export their values to their own module, iff it exists.

  • Allow @staticmethod decorator to declare static cdef methods. This is especially useful for declaring “constructors” for cdef classes that can take non-Python arguments.

  • Taking a char* from a temporary Python string object is safer in more cases and can be done inside of non-trivial expressions, including arguments of a function call. A compile time error is raised only when such a pointer is assigned to a variable and would thus exceed the lifetime of the string itself.

  • Generators have new properties __name__ and __qualname__ that provide the plain/qualified name of the generator function (following CPython 3.5). See

  • The inline function modifier is available as a decorator @cython.inline in pure mode.

  • When cygdb is run in a virtualenv, it enables the same virtualenv inside of the debugger. Patch by Marc Abramowitz.

  • PEP 465: dedicated infix operator for matrix multiplication (A @ B).

  • HTML output of annotated code uses Pygments for code highlighting and generally received a major overhaul by Matthias Bussonier.

  • IPython magic support is now available directly from Cython with the command “%load_ext cython”. Cython code can directly be executed in a cell when marked with “%%cython”. Code analysis is available with “%%cython -a”. Patch by Martín Gaitán.

  • Simple support for declaring Python object types in Python signature annotations. Currently requires setting the compiler directive annotation_typing=True.

  • New directive use_switch (defaults to True) to optionally disable the optimization of chained if statement to C switch statements.

  • Defines dynamic_cast et al. in libcpp.cast and C++ heap data structure operations in libcpp.algorithm.

  • Shipped header declarations in posix.* were extended to cover more of the POSIX API. Patches by Lars Buitinck and Mark Peek.


  • Simple calls to C implemented Python functions/methods are faster. This also speeds up many operations on builtins that Cython cannot otherwise optimise.

  • The “and”/”or” operators try to avoid unnecessary coercions of their arguments. They now evaluate the truth value of each argument independently and only coerce the final result of the whole expression to the target type (e.g. the type on the left side of an assignment). This also avoids reference counting overhead for Python values during evaluation and generally improves the code flow in the generated C code.

  • The Python expression “2 ** N” is optimised into bit shifting. See

  • Cascaded assignments (a = b = …) try to minimise the number of type coercions.

  • Calls to slice() are translated to a straight C-API call.

Bugs fixed

  • Crash when assigning memory views from ternary conditional expressions.

  • Nested C++ templates could lead to unseparated “>>” characters being generated into the C++ declarations, which older C++ compilers could not parse.

  • Sending SIGINT (Ctrl-C) during parallel cythonize() builds could hang the child processes.

  • No longer ignore local setup.cfg files for distutils in pyximport. Patch by Martin Teichmann.

  • Taking a char* from an indexed Python string generated unsafe reference counting code.

  • Set literals now create all of their items before trying to add them to the set, following the behaviour in CPython. This makes a difference in the rare case that the item creation has side effects and some items are not hashable (or if hashing them has side effects, too).

  • Cython no longer generates the cross product of C functions for code that uses memory views of fused types in function signatures (e.g. cdef func(floating[:] a, floating[:] b)). This is considered the expected behaviour by most users and was previously inconsistent with other structured types like C arrays. Code that really wants all type combinations can create the same fused memoryview type under different names and use those in the signature to make it clear which types are independent.

  • Names that were unknown at compile time were looked up as builtins at runtime but not as global module names. Trying both lookups helps with globals() manipulation.

  • Fixed stl container conversion for typedef element types.

  • obj.pop(x) truncated large C integer values of x to Py_ssize_t.

  • __init__.pyc is recognised as marking a package directory (in addition to .py, .pyx and .pxd).

  • Syntax highlighting in cython-mode.el for Emacs no longer incorrectly highlights keywords found as part of longer names.

  • Correctly handle from cython.submodule cimport name.

  • Fix infinite recursion when using super with cpdef methods.

  • No-args dir() was not guaranteed to return a sorted list.

Other changes

  • The header line in the generated C files no longer contains the timestamp but only the Cython version that wrote it. This was changed to make builds more reproducible.

  • Removed support for CPython 2.4, 2.5 and 3.1.

  • The licensing implications on the generated code were clarified to avoid legal constraints for users.

0.20.2 (2014-06-16)

Features added

  • Some optimisations for set/frozenset instantiation.

  • Support for C++ unordered_set and unordered_map.

Bugs fixed

  • Access to attributes of optimised builtin methods (e.g. [].append.__name__) could fail to compile.

  • Memory leak when extension subtypes add a memory view as attribute to those of the parent type without having Python object attributes or a user provided dealloc method.

  • Compiler crash on readonly properties in “binding” mode.

  • Auto-encoding with c_string_encoding=ascii failed in Py3.3.

  • Crash when subtyping freelist enabled Cython extension types with Python classes that use __slots__.

  • Freelist usage is restricted to CPython to avoid problems with other Python implementations.

  • Memory leak in memory views when copying overlapping, contiguous slices.

  • Format checking when requesting non-contiguous buffers from cython.array objects was accidentally omitted in Py3.

  • C++ destructor calls in extension types could fail to compile in clang.

  • Buffer format validation failed for sequences of strings in structs.

  • Docstrings on extension type attributes in .pxd files were rejected.

0.20.1 (2014-02-11)

Bugs fixed

  • Build error under recent MacOS-X versions where isspace() could not be resolved by clang.

  • List/Tuple literals multiplied by more than one factor were only multiplied by the last factor instead of all.

  • Lookups of special methods (specifically for context managers) could fail in Python <= 2.6/3.1.

  • Local variables were erroneously appended to the signature introspection of Cython implemented functions with keyword-only arguments under Python 3.

  • In-place assignments to variables with inferred Python builtin/extension types could fail with type errors if the result value type was incompatible with the type of the previous value.

  • The C code generation order of cdef classes, closures, helper code, etc. was not deterministic, thus leading to high code churn.

  • Type inference could fail to deduce C enum types.

  • Type inference could deduce unsafe or inefficient types from integer assignments within a mix of inferred Python variables and integer variables.

0.20 (2014-01-18)

Features added

  • Support for CPython 3.4.

  • Support for calling C++ template functions.

  • yield is supported in finally clauses.

  • The C code generated for finally blocks is duplicated for each exit case to allow for better optimisations by the C compiler.

  • Cython tries to undo the Python optimisationism of assigning a bound method to a local variable when it can generate better code for the direct call.

  • Constant Python float values are cached.

  • String equality comparisons can use faster type specific code in more cases than before.

  • String/Unicode formatting using the ‘%’ operator uses a faster C-API call.

  • bytearray has become a known type and supports coercion from and to C strings. Indexing, slicing and decoding is optimised. Note that this may have an impact on existing code due to type inference.

  • Using cdef basestring stringvar and function arguments typed as basestring is now meaningful and allows assigning exactly str and unicode objects, but no subtypes of these types.

  • Support for the __debug__ builtin.

  • Assertions in Cython compiled modules are disabled if the running Python interpreter was started with the “-O” option.

  • Some types that Cython provides internally, such as functions and generators, are now shared across modules if more than one Cython implemented module is imported.

  • The type inference algorithm works more fine granular by taking the results of the control flow analysis into account.

  • A new script in bin/cythonize provides a command line frontend to the cythonize() compilation function (including distutils build).

  • The new extension type decorator @cython.no_gc_clear prevents objects from being cleared during cyclic garbage collection, thus making sure that object attributes are kept alive until deallocation.

  • During cyclic garbage collection, attributes of extension types that cannot create reference cycles due to their type (e.g. strings) are no longer considered for traversal or clearing. This can reduce the processing overhead when searching for or cleaning up reference cycles.

  • Package compilation (i.e. files) now works, starting with Python 3.3.

  • The cython-mode.el script for Emacs was updated. Patch by Ivan Andrus.

  • An option common_utility_include_dir was added to cythonize() to save oft-used utility code once in a separate directory rather than as part of each generated file.

  • unraisable_tracebacks directive added to control printing of tracebacks of unraisable exceptions.

Bugs fixed

  • Abstract Python classes that subtyped a Cython extension type failed to raise an exception on instantiation, and thus ended up being instantiated.

  • set.add(a_tuple) and set.discard(a_tuple) failed with a TypeError in Py2.4.

  • The PEP 3155 __qualname__ was incorrect for nested classes and inner classes/functions declared as global.

  • Several corner cases in the try-finally statement were fixed.

  • The metaclass of a Python class was not inherited from its parent class(es). It is now extracted from the list of base classes if not provided explicitly using the Py3 metaclass keyword argument. In Py2 compilation mode, a __metaclass__ entry in the class dict will still take precedence if not using Py3 metaclass syntax, but only after creating the class dict (which may have been done by a metaclass of a base class, see PEP 3115). It is generally recommended to use the explicit Py3 syntax to define metaclasses for Python types at compile time.

  • The automatic C switch statement generation behaves more safely for heterogeneous value types (e.g. mixing enum and char), allowing for a slightly wider application and reducing corner cases. It now always generates a ‘default’ clause to avoid C compiler warnings about unmatched enum values.

  • Fixed a bug where class hierarchies declared out-of-order could result in broken generated code.

  • Fixed a bug which prevented overriding const methods of C++ classes.

  • Fixed a crash when converting Python objects to C++ strings fails.

Other changes

  • In Py3 compilation mode, Python2-style metaclasses declared by a __metaclass__ class dict entry are ignored.

  • In Py3.4+, the Cython generator type uses tp_finalize() for safer cleanup instead of tp_del().

0.19.2 (2013-10-13)

Features added

Bugs fixed

  • Some standard declarations were fixed or updated, including the previously incorrect declaration of PyBuffer_FillInfo() and some missing bits in libc.math.

  • Heap allocated subtypes of type used the wrong base type struct at the C level.

  • Calling the unbound method dict.keys/value/items() in dict subtypes could call the bound object method instead of the unbound supertype method.

  • “yield” wasn’t supported in “return” value expressions.

  • Using the “bint” type in memory views lead to unexpected results. It is now an error.

  • Assignments to global/closure variables could catch them in an illegal state while deallocating the old value.

Other changes

0.19.1 (2013-05-11)

Features added

  • Completely empty C-API structs for extension type slots (protocols like number/mapping/sequence) are no longer generated into the C code.

  • Docstrings that directly follow a public/readonly attribute declaration in a cdef class will be used as docstring of the auto-generated property. This fixes ticket 206.

  • The automatic signature documentation tries to preserve more semantics of default arguments and argument types. Specifically, bint arguments now appear as type bool.

  • A warning is emitted when negative literal indices are found inside of a code section that disables wraparound handling. This helps with fixing invalid code that might fail in the face of future compiler optimisations.

  • Constant folding for boolean expressions (and/or) was improved.

  • Added a build_dir option to cythonize() which allows one to place the generated .c files outside the source tree.

Bugs fixed

  • isinstance(X, type) failed to get optimised into a call to PyType_Check(), as done for other builtin types.

  • A spurious from datetime cimport * was removed from the “cpython” declaration package. This means that the “datetime” declarations (added in 0.19) are no longer available directly from the “cpython” namespace, but only from “cpython.datetime”. This is the correct way of doing it because the declarations refer to a standard library module, not the core CPython C-API itself.

  • The C code for extension types is now generated in topological order instead of source code order to avoid C compiler errors about missing declarations for subtypes that are defined before their parent.

  • The memoryview type name no longer shows up in the module dict of modules that use memory views. This fixes trac ticket 775.

  • Regression in 0.19 that rejected valid C expressions from being used in C array size declarations.

  • In C++ mode, the C99-only keyword restrict could accidentally be seen by the GNU C++ compiler. It is now specially handled for both GCC and MSVC.

  • Testing large (> int) C integer values for their truth value could fail due to integer wrap-around.

Other changes

0.19 (2013-04-19)

Features added

  • New directives c_string_type and c_string_encoding to more easily and automatically convert between C strings and the different Python string types.

  • The extension type flag Py_TPFLAGS_HAVE_VERSION_TAG is enabled by default on extension types and can be disabled using the type_version_tag compiler directive.

  • EXPERIMENTAL support for simple Cython code level line tracing. Enabled by the “linetrace” compiler directive.

  • Cython implemented functions make their argument and return type annotations available through the __annotations__ attribute (PEP 3107).

  • Access to non-cdef module globals and Python object attributes is faster.

  • Py_UNICODE* coerces from and to Python unicode strings. This is helpful when talking to Windows APIs, which use compatible wchar_t arrays for strings. Note that the Py_UNICODE type is otherwise deprecated as of CPython 3.3.

  • isinstance(obj, basestring) is optimised. In Python 3 it only tests for instances of str (i.e. Py2 unicode).

  • The basestring builtin is mapped to str (i.e. Py2 unicode) when compiling the generated C code under Python 3.

  • Closures use freelists, which can speed up their creation quite substantially. This is also visible for short running generator expressions, for example.

  • A new class decorator @cython.freelist(N) creates a static freelist of N instances for an extension type, thus avoiding the costly allocation step if possible. This can speed up object instantiation by 20-30% in suitable scenarios. Note that freelists are currently only supported for base types, not for types that inherit from others.

  • Fast extension type instantiation using the Type.__new__(Type) idiom has gained support for passing arguments. It is also a bit faster for types defined inside of the module.

  • The Python2-only dict methods .iter*() and .view*() (requires Python 2.7) are automatically mapped to the equivalent keys/values/items methods in Python 3 for typed dictionaries.

  • Slicing unicode strings, lists and tuples is faster.

  • list.append() is faster on average.

  • raise Exception() from None suppresses the exception context in Py3.3.

  • Py3 compatible exec(tuple) syntax is supported in Py2 code.

  • Keyword arguments are supported for cdef functions.

  • External C++ classes can be declared nogil. Patch by John Stumpo. This fixes trac ticket 805.

Bugs fixed

  • 2-value slicing of unknown objects passes the correct slice when the getitem protocol is used instead of the getslice protocol (especially in Python 3), i.e. None values for missing bounds instead of [0,maxsize]. It is also a bit faster in some cases, e.g. for constant bounds. This fixes trac ticket 636.

  • Cascaded assignments of None values to extension type variables failed with a TypeError at runtime.

  • The __defaults__ attribute was not writable for Cython implemented functions.

  • Default values of keyword-only arguments showed up in __defaults__ instead of __kwdefaults__ (which was not implemented). Both are available for Cython implemented functions now, as specified in Python 3.x.

  • yield works inside of with gil sections. It previously lead to a crash. This fixes trac ticket 803.

  • Static methods without explicitly named positional arguments (e.g. having only *args) crashed when being called. This fixes trac ticket 804.

  • dir() without arguments previously returned an unsorted list, which now gets sorted as expected.

  • dict.items(), dict.keys() and dict.values() no longer return lists in Python 3.

  • Exiting from an except-as clause now deletes the exception in Python 3 mode.

  • The declarations of frexp() and ldexp() in math.pxd were incorrect.

Other changes

0.18 (2013-01-28)

Features added

  • Named Unicode escapes (”N{…}”) are supported.

  • Python functions/classes provide the special attribute “__qualname__” as defined by PEP 3155.

  • Added a directive overflowcheck which raises an OverflowException when arithmetic with C ints overflow. This has a modest performance penalty, but is much faster than using Python ints.

  • Calls to nested Python functions are resolved at compile time.

  • Type inference works across nested functions.

  • py_bytes_string.decode(...) is optimised.

  • C const declarations are supported in the language.

Bugs fixed

  • Automatic C++ exception mapping didn’t work in nogil functions (only in “with nogil” blocks).

Other changes

0.17.4 (2013-01-03)

Bugs fixed

  • Garbage collection triggered during deallocation of container classes could lead to a double-deallocation.

0.17.3 (2012-12-14)

Features added

Bugs fixed

  • During final interpreter cleanup (with types cleanup enabled at compile time), extension types that inherit from base types over more than one level that were cimported from other modules could lead to a crash.

  • Weak-reference support in extension types (with a cdef __weakref__ attribute) generated incorrect deallocation code.

  • In CPython 3.3, converting a Unicode character to the Py_UNICODE type could fail to raise an overflow for non-BMP characters that do not fit into a wchar_t on the current platform.

  • Negative C integer constants lost their longness suffix in the generated C code.

Other changes

0.17.2 (2012-11-20)

Features added

  • cythonize() gained a best effort compile mode that can be used to simply ignore .py files that fail to compile.

Bugs fixed

  • Replacing an object reference with the value of one of its cdef attributes could generate incorrect C code that accessed the object after deleting its last reference.

  • C-to-Python type coercions during cascaded comparisons could generate invalid C code, specifically when using the ‘in’ operator.

  • “obj[1,]” passed a single integer into the item getter instead of a tuple.

  • Cyclic imports at module init time did not work in Py3.

  • The names of C++ destructors for template classes were built incorrectly.

  • In pure mode, type casts in Cython syntax and the C ampersand operator are now rejected. Use the pure mode replacements instead.

  • In pure mode, C type names and the sizeof() function are no longer recognised as such and can be used as normal Python names.

  • The extended C level support for the CPython array type was declared too late to be used by user defined classes.

  • C++ class nesting was broken.

  • Better checking for required nullary constructors for stack-allocated C++ instances.

  • Remove module docstring in no-docstring mode.

  • Fix specialization for varargs function signatures.

  • Fix several compiler crashes.

Other changes

  • An experimental distutils script for compiling the CPython standard library was added as Tools/

0.17.1 (2012-09-26)

Features added

Bugs fixed

  • A reference leak was fixed in the new dict iteration code when the loop target was not a plain variable but an unpacked tuple.

  • Memory views did not handle the special case of a NULL buffer strides value, as allowed by PEP3118.

Other changes

0.17 (2012-09-01)

Features added

  • Alpha quality support for compiling and running Cython generated extension modules in PyPy (through cpyext). Note that this requires at least PyPy 1.9 and in many cases also adaptations in user code, especially to avoid borrowed references when no owned reference is being held directly in C space (a reference in a Python list or dict is not enough, for example). See the documentation on porting Cython code to PyPy.

  • “yield from” is supported (PEP 380) and a couple of minor problems with generators were fixed.

  • C++ STL container classes automatically coerce from and to the equivalent Python container types on typed assignments and casts. Note that the data in the containers is copied during this conversion.

  • C++ iterators can now be iterated over using “for x in cpp_container” whenever cpp_container has begin() and end() methods returning objects satisfying the iterator pattern (that is, it can be incremented, dereferenced, and compared (for non-equality)).

  • cdef classes can now have C++ class members (provided a zero-argument constructor exists)

  • A new cpython.array standard cimport file allows to efficiently talk to the stdlib array.array data type in Python 2. Since CPython does not export an official C-API for this module, it receives special casing by the compiler in order to avoid setup overhead on user side. In Python 3, both buffers and memory views on the array type already worked out of the box with earlier versions of Cython due to the native support for the buffer interface in the Py3 array module.

  • Fast dict iteration is now enabled optimistically also for untyped variables when the common iteration methods are used.

  • The unicode string processing code was adapted for the upcoming CPython 3.3 (PEP 393, new Unicode buffer layout).

  • Buffer arguments and memory view arguments in Python functions can be declared “not None” to raise a TypeError on None input.

  • c(p)def functions in pure mode can specify their return type with “@cython.returns()”.

  • Automatic dispatch for fused functions with memoryview arguments

  • Support newaxis indexing for memoryviews

  • Support decorators for fused functions

Bugs fixed

  • Old-style Py2 imports did not work reliably in Python 3.x and were broken in Python 3.3. Regardless of this fix, it’s generally best to be explicit about relative and global imports in Cython code because old-style imports have a higher overhead. To this end, “from __future__ import absolute_import” is supported in Python/Cython 2.x code now (previous versions of Cython already used it when compiling Python 3 code).

  • Stricter constraints on the “inline” and “final” modifiers. If your code does not compile due to this change, chances are these modifiers were previously being ignored by the compiler and can be removed without any performance regression.

  • Exceptions are always instantiated while raising them (as in Python), instead of risking to instantiate them in potentially unsafe situations when they need to be handled or otherwise processed.

  • locals() properly ignores names that do not have Python compatible types (including automatically inferred types).

  • Some garbage collection issues of memory views were fixed.

  • numpy.pxd compiles in Python 3 mode.

  • Several C compiler warnings were fixed.

  • Several bugs related to memoryviews and fused types were fixed.

  • Several bug-fixes and improvements related to cythonize(), including ccache-style caching.

Other changes

  • libc.string provides a convenience declaration for const uchar in addition to const char.

  • User declared char* types are now recognised as such and auto-coerce to and from Python bytes strings.

  • callable() and next() compile to more efficient C code.

  • list.append() is faster on average.

  • Modules generated by @cython.inline() are written into the directory pointed to by the environment variable CYTHON_CACHE_DIR if set.

0.16 (2012-04-21)

Features added

  • Enhancements to Cython’s function type (support for weak references, default arguments, code objects, dynamic attributes, classmethods, staticmethods, and more)

  • Fused Types - Template-like support for functions and methods CEP 522 (docs)

  • Typed views on memory - Support for efficient direct and indirect buffers (indexing, slicing, transposing, …) CEP 517 (docs)

  • super() without arguments

  • Final cdef methods (which translate into direct calls on known instances)

Bugs fixed

  • fix alignment handling for record types in buffer support

Other changes

  • support default arguments for closures

  • search sys.path for pxd files

  • support C++ template casting

  • faster traceback building and faster generator termination

  • support inplace operators on indexed buffers

  • allow nested prange sections

0.15.1 (2011-09-19)

Features added

Bugs fixed

Other changes

0.15 (2011-08-05)

Features added

  • Generators (yield) - Cython has full support for generators, generator expressions and PEP 342 coroutines.

  • The nonlocal keyword is supported.

  • Re-acquiring the gil: with gil - works as expected within a nogil context.

  • OpenMP support: prange.

  • Control flow analysis prunes dead code and emits warnings and errors about uninitialised variables.

  • Debugger command cy set to assign values of expressions to Cython variables and cy exec counterpart $cy_eval().

  • Exception chaining PEP 3134.

  • Relative imports PEP 328.

  • Improved pure syntax including cython.cclass, cython.cfunc, and cython.ccall.

  • The with statement has its own dedicated and faster C implementation.

  • Support for del.

  • Boundschecking directives implemented for builtin Python sequence types.

  • Several updates and additions to the shipped standard library .pxd files.

  • Forward declaration of types is no longer required for circular references.

Bugs fixed

Other changes

  • Uninitialized variables are no longer initialized to None and accessing them has the same semantics as standard Python.

  • globals() now returns a read-only dict of the Cython module’s globals, rather than the globals of the first non-Cython module in the stack

  • Many C++ exceptions are now special cased to give closer Python counterparts. This means that except+ functions that formerly raised generic RuntimeErrors may raise something else such as ArithmeticError.

  • The inlined generator expressions (introduced in Cython 0.13) were disabled in favour of full generator expression support. This breaks code that previously used them inside of cdef functions (usage in def functions continues to work) and induces a performance regression for cases that continue to work but that were previously inlined. We hope to reinstate this feature in the near future.

0.14.1 (2011-02-04)

Features added

  • The gdb debugging support was extended to include all major Cython features, including closures.

  • raise MemoryError() is now safe to use as Cython replaces it with the correct C-API call.

Bugs fixed

Other changes

  • Decorators on special methods of cdef classes now raise a compile time error rather than being ignored.

  • In Python 3 language level mode (-3 option), the ‘str’ type is now mapped to ‘unicode’, so that cdef str s declares a Unicode string even when running in Python 2.

0.14 (2010-12-14)

Features added

  • Python classes can now be nested and receive a proper closure at definition time.

  • Redefinition is supported for Python functions, even within the same scope.

  • Lambda expressions are supported in class bodies and at the module level.

  • Metaclasses are supported for Python classes, both in Python 2 and Python 3 syntax. The Python 3 syntax (using a keyword argument in the type declaration) is preferred and optimised at compile time.

  • “final” extension classes prevent inheritance in Python space. This feature is available through the new “” decorator. In the future, these classes may receive further optimisations.

  • “internal” extension classes do not show up in the module dictionary. This feature is available through the new “cython.internal” decorator.

  • Extension type inheritance from builtin types, such as “cdef class MyUnicode(unicode)”, now works without further external type redeclarations (which are also strongly discouraged now and continue to issue a warning).

  • GDB support.

  • A new build system with support for inline distutils directives, correct dependency tracking, and parallel compilation.

  • Support for dynamic compilation at runtime via the new cython.inline function and cython.compile decorator.

  • “nogil” blocks are supported when compiling pure Python code by writing “with cython.nogil”.

  • Iterating over arbitrary pointer types is now supported, as is an optimized version of the in operator, e.g. x in ptr[a:b].

Bugs fixed

  • In parallel assignments, the right side was evaluated in reverse order in 0.13. This could result in errors if it had side effects (e.g. function calls).

  • In some cases, methods of builtin types would raise a SystemError instead of an AttributeError when called on None.

Other changes

  • Constant tuples are now cached over the lifetime of an extension module, just like CPython does. Constant argument tuples of Python function calls are also cached.

  • Closures have tightened to include exactly the names used in the inner functions and classes. Previously, they held the complete locals of the defining function.

  • The builtin “next()” function in Python 2.6 and later is now implemented internally and therefore available in all Python versions. This makes it the preferred and portable way of manually advancing an iterator.

  • In addition to the previously supported inlined generator expressions in 0.13, “sorted(genexpr)” can now be used as well. Typing issues were fixed in “sum(genexpr)” that could lead to invalid C code being generated. Other known issues with inlined generator expressions were also fixed that make upgrading to 0.14 a strong recommendation for code that uses them. Note that general generators and generator expressions continue to be not supported.

  • Inplace arithmetic operators now respect the cdivision directive and are supported for complex types.

  • Typing a variable as type “complex” previously gave it the Python object type. It now uses the appropriate C/C++ double complex type. A side-effect is that assignments and typed function parameters now accept anything that Python can coerce to a complex, including integers and floats, and not only complex instances.

  • Large integer literals pass through the compiler in a safer way. To prevent truncation in C code, non 32-bit literals are turned into Python objects if not used in a C context. This context can either be given by a clear C literal suffix such as “UL” or “LL” (or “L” in Python 3 code), or it can be an assignment to a typed variable or a typed function argument, in which case it is up to the user to take care of a sufficiently large value space of the target.

  • Python functions are declared in the order they appear in the file, rather than all being created at module creation time. This is consistent with Python and needed to support, for example, conditional or repeated declarations of functions. In the face of circular imports this may cause code to break, so a new –disable-function-redefinition flag was added to revert to the old behavior. This flag will be removed in a future release, so should only be used as a stopgap until old code can be fixed.

0.13 (2010-08-25)

Features added

  • Closures are fully supported for Python functions. Cython supports inner functions and lambda expressions. Generators and generator expressions are not supported in this release.

  • Proper C++ support. Cython knows about C++ classes, templates and overloaded function signatures, so that Cython code can interact with them in a straight forward way.

  • Type inference is enabled by default for safe C types (e.g. double, bint, C++ classes) and known extension types. This reduces the need for explicit type declarations and can improve the performance of untyped code in some cases. There is also a verbose compile mode for testing the impact on user code.

  • Cython’s for-in-loop can iterate over C arrays and sliced pointers. The type of the loop variable will be inferred automatically in this case.

  • The Py_UNICODE integer type for Unicode code points is fully supported, including for-loops and ‘in’ tests on unicode strings. It coerces from and to single character unicode strings. Note that untyped for-loop variables will automatically be inferred as Py_UNICODE when iterating over a unicode string. In most cases, this will be much more efficient than yielding sliced string objects, but can also have a negative performance impact when the variable is used in a Python context multiple times, so that it needs to coerce to a unicode string object more than once. If this happens, typing the loop variable as unicode or object will help.

  • The built-in functions any(), all(), sum(), list(), set() and dict() are inlined as plain for loops when called on generator expressions. Note that generator expressions are not generally supported apart from this feature. Also, tuple(genexpr) is not currently supported - use tuple([listcomp]) instead.

  • More shipped standard library declarations. The python_* and stdlib/stdio .pxd files have been deprecated in favor of clib.* and cpython[.*] and may get removed in a future release.

  • Pure Python mode no longer disallows non-Python keywords like ‘cdef’, ‘include’ or ‘cimport’. It also no longer recognises syntax extensions like the for-from loop.

  • Parsing has improved for Python 3 syntax in Python code, although not all features are correctly supported. The missing Python 3 features are being worked on for the next release.

  • from __future__ import print_function is supported in Python 2.6 and later. Note that there is currently no emulation for earlier Python versions, so code that uses print() with this future import will require at least Python 2.6.

  • New compiler directive language_level (valid values: 2 or 3) with corresponding command line options -2 and -3 requests source code compatibility with Python 2.x or Python 3.x respectively. Language level 3 currently enforces unicode literals for unprefixed string literals, enables the print function (requires Python 2.6 or later) and keeps loop variables in list comprehensions from leaking.

  • Loop variables in set/dict comprehensions no longer leak into the surrounding scope (following Python 2.7). List comprehensions are unchanged in language level 2.

  • print >> stream

Bugs fixed

Other changes

  • The availability of type inference by default means that Cython will also infer the type of pointers on assignments. Previously, code like this:

    cdef char* s = ...
    untyped_variable = s

    would convert the char* to a Python bytes string and assign that. This is no longer the case and no coercion will happen in the example above. The correct way of doing this is through an explicit cast or by typing the target variable, i.e.

    cdef char* s = ...
    untyped_variable1 = <bytes>s
    untyped_variable2 = <object>s
    cdef object py_object = s
    cdef bytes  bytes_string = s
  • bool is no longer a valid type name by default. The problem is that it’s not clear whether bool should refer to the Python type or the C++ type, and expecting one and finding the other has already led to several hard-to-find bugs. Both types are available for importing: you can use from cpython cimport bool for the Python bool type, and from libcpp cimport bool for the C++ type. bool is still a valid object by default, so one can still write bool(x).

  • __getsegcount__ is now correctly typed to take a Py_size_t* rather than an int*.

0.12.1 (2010-02-02)

Features added

  • Type inference improvements.

    • There have been several bug fixes and improvements to the type inferencer.

    • Notably, there is now a “safe” mode enabled by setting the infer_types directive to None. (The None here refers to the “default” mode, which will be the default in 0.13.) This safe mode limits inference to Python object types and C doubles, which should speed up execution without affecting any semantics such as integer overflow behavior like infer_types=True might. There is also an infer_types.verbose option which allows one to see what types are inferred.

  • The boundscheck directive works for lists and tuples as well as buffers.

  • len(s) and s.decode(“encoding”) are efficiently supported for char* s.

  • Cython’s INLINE macro has been renamed to CYTHON_INLINE to reduce conflict and has better support for the MSVC compiler on Windows. It is no longer clobbered if externally defined.

  • Revision history is now omitted from the source package, resulting in a 85% size reduction. Running make repo will download the history and turn the directory into a complete Mercurial working repository.

  • Cython modules don’t need to be recompiled when the size of an external type grows. (A warning, rather than an error, is produced.) This should be helpful for binary distributions relying on NumPy.

Bugs fixed

  • Several other bugs and minor improvements have been made. This release should be fully backwards compatible with 0.12.

Other changes

0.12 (2009-11-23)

Features added

  • Type inference with the infer_types directive

  • Seamless C++ complex support

  • Fast extension type instantiation using the normal Python meme obj = MyType.__new__(MyType)

  • Improved support for Py3.1

  • Cython now runs under Python 3.x using the 2to3 tool

  • unittest support for doctests in Cython modules

  • Optimised handling of C strings (char*): for c in cstring[2:50] and cstring.decode()

  • Looping over c pointers: for i in intptr[:50].

  • pyximport improvements

  • cython_freeze improvements

Bugs fixed

  • Many bug fixes

Other changes

  • Many other optimisation, e.g. enumerate() loops, parallel swap assignments (a,b = b,a), and unicode.encode()

  • More complete numpy.pxd

0.11.2 (2009-05-20)

Features added

  • There’s now native complex floating point support! C99 complex will be used if complex.h is included, otherwise explicit complex arithmetic working on all C compilers is used. [Robert Bradshaw]

    cdef double complex a = 1 + 0.3j
    cdef np.ndarray[np.complex128_t, ndim=2] arr = \
       np.zeros(10, np.complex128)
  • Cython can now generate a main()-method for embedding of the Python interpreter into an executable (see #289) [Robert Bradshaw]

  • @wraparound directive (another way to disable arr[idx] for negative idx) [Dag Sverre Seljebotn]

  • Correct support for NumPy record dtypes with different alignments, and “cdef packed struct” support [Dag Sverre Seljebotn]

  • @callspec directive, allowing custom calling convention macros [Lisandro Dalcin]

Bugs fixed

Other changes

  • Bug fixes and smaller improvements. For the full list, see [1].