Cython 3.0a6 releases: C-Extensions for Python
3 min readCython is a programming language that makes writing C extensions for the Python language as easy as Python itself. It aims to become a superset of the Python language which gives it high-level, object-oriented, functional, and dynamic programming. Its main feature on top of these is support for optional static type declarations as part of the language. The source code gets translated into optimized C/C++ code and compiled as Python extension modules. This allows for both very fast program execution and tight integration with external C libraries, while keeping up the high programmer productivity for which the Python language is well known.
The primary Python execution environment is commonly referred to as CPython, as it is written in C. Other major implementations use Java (Jython [Jython]), C# (IronPython [IronPython]) and Python itself (PyPy [PyPy]). Written in C, CPython has been conducive to wrapping many external libraries that interface through the C language. It has, however, remained non trivial to write the necessary glue code in C, especially for programmers who are more fluent in a high-level language like Python than in a close-to-the-metal language like C.
Changelog Cython v3.0a6
Features added
- Special methods for binary operators now follow Python semantics. Rather than e.g. a single
__add__method for cdef classes, where “self” can be either the first or second argument, one can now define both__add__and__radd__as for standard Python classes. This behavior can be disabled with thec_api_binop_methodsdirective to return to the previous semantics in Cython code (available from Cython 0.29.20), or the reversed method (__radd__) can be implemented in addition to an existing two-sided operator method (__add__) to get a backwards compatible implementation. (Github issue #2056) - No/single argument functions now accept keyword arguments by default in order to comply with Python semantics. The marginally faster calling conventions
METH_NOARGSandMETH_Othat reject keyword arguments are still available with the directive@cython.always_allow_keywords(False). (Github issue #3090) - For-in-loop iteration over
bytearrayand memory views is optimised. Patch by David Woods. (Github issue #2227) - Type inference now works for memory views and slices. Patch by David Woods. (Github issue #2227)
- The
@returns()decorator propagates exceptions by default for suitable C return types when no@exceptval()is defined. (Github issues #3625, #3664) - A low-level inline function
total_seconds(timedelta)was added tocpython.datetimeto bypass the Python method call. Note that this function is not guaranteed to give exactly the same results for very large time intervals. Patch by Brock Mendel. (Github issue #3616) - Type inference now understands that
a, *b = xassigns a list tob. - Limited API support was improved. Patches by Matthias Braun. (Github issues #3693, #3707)
- The Cython
CodeWritercan now handle more syntax constructs. Patch by Tao He. (Github issue #3514)
Bugs fixed
- The construct
for x in cpp_function_call()failed to compile. Patch by David Woods. (Github issue #3663) - C++ references failed to compile when used as Python object indexes. Patch by David Woods. (Github issue #3754)
- The C++
typeid()function was allowed in C mode. Patch by Celelibi. (Github issue #3637) repr()was assumed to returnstrinstead ofunicodewithlanguage_level=3. (Github issue #3736)- Includes all bug-fixes from the 0.29.21 release.
Other changes
- The
numpydeclarations were updated. Patch by Brock Mendel. (Github issue #3630) - The names of Cython’s internal types (functions, generator, coroutine, etc.) are now qualified with the module name of the internal Cython module that is used for sharing them across Cython implemented modules, for example
_cython_3_0a5.coroutine. This was done to avoid making them look like homeless builtins, to help with debugging, and in order to avoid a CPython warning according to https://bugs.python.org/issue20204
