The Cython language makes writing C extensions for the Python language as
easy as Python itself. Cython is a source code translator based on Pyrex_,
but supports more cutting edge functionality and optimizations.

The Cython language is a superset of the Python language (almost all Python
code is also valid Cython code), but Cython additionally supports optional
static typing to natively call C functions, operate with C++ classes and
declare fast C types on variables and class attributes. This allows the
compiler to generate very efficient C code from Cython code.

This makes Cython the ideal language for writing glue code for external
C/C++ libraries, and for fast C modules that speed up the execution of
Python code.

The newest Cython release can always be downloaded from https://cython.org/.
Unpack the tarball or zip file, enter the directory, and then run::

pip install .

Note that for one-time builds, e.g. for CI/testing, on platforms that are not
covered by one of the wheel packages provided on PyPI and the pure Python wheel
that we provide is not used, it is substantially faster than a full source build
to install an uncompiled (slower) version of Cython with::

NO_CYTHON_COMPILE=true pip install .

.. _Pyrex: https://www.cosc.canterbury.ac.nz/greg.ewing/python/Pyrex/

3.1.3 (2025-08-13)

Bugs fixed

Some method calls with 0 or 1 argument failed to use PyObject_VectorCallMethod().
Walrus assignments of literal Python integers could generate invalid C code.
(Github issue https://github.com/cython/cython/issues/6989)
cython.pythread_type_lock (also used as fallback for cython.pymutex)
could stall on heavily contended locks.
(Github issue https://github.com/cython/cython/issues/6999)
C string arrays (not pointers) always coerced to the Python default string type,
even on explicit casts to other string types.
(Github issue https://github.com/cython/cython/issues/7020)
Unterminated \N{} character escapes in strings could unrail the parser.
(Github issue https://github.com/cython/cython/issues/7056)
An internal C function was not marked as static and leaked a linker symbol.
(Github issue https://github.com/cython/cython/issues/6957)
Some Unicode letters were not recognised as lexically valid name parts.
(Github issue https://github.com/cython/cython/issues/7059)
Compatibility with PyPy3.8 was lost by accident.
The Linux binary wheels of 3.1.2 used SSSE3 CPU instructions which are not available on some CPUs.
(Github issue https://github.com/cython/cython/issues/7038)

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