Cython 3.2.5

The Cython compiler for writing C extensions in the Python language.

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 .

3.2.5 (2026-05-23)

Bugs fixed

• A compile failure was fixed when using the walrus operator inside of try-except. (Github issue https://github.com/cython/cython/issues/7462)

• Expressions with side-effects as object argument to isinstance() could get evaluated multiple times, e.g. when they use the walrus operator. (Github issue https://github.com/cython/cython/issues/7670)

• Several problems generating the shared utility module were resolved, including a performance regression with memory views. (Github issues https://github.com/cython/cython/issues/7487, https://github.com/cython/cython/issues/7497, https://github.com/cython/cython/issues/7504, https://github.com/cython/cython/issues/7558)

• Some GC and refcounting issues were resolved for Cython functions in the Limited API. (Github issue https://github.com/cython/cython/issues/7594)

• Refcounting errors and error handling issues were resolved in some rare error handling cases. (Github issues https://github.com/cython/cython/issues/7597, https://github.com/cython/cython/issues/7599, https://github.com/cython/cython/issues/7612, https://github.com/cython/cython/issues/7673)

• Using cython.pymutex in an extension type with cdef methods generated invalid C code missing the required PyMutex declarations. (Github issue https://github.com/cython/cython/issues/6995)

• Calling .get_frame() on Cython coroutines could crash in freethreading Python. (Github issue https://github.com/cython/cython/issues/7632)

• The vectorcall protocol was not used correctly in .throw() of Cython coroutines when raising the exception only by type (without value or traceback). (Github issue https://github.com/cython/cython/issues/7677)

• A problem with cpdef enums in the Limited API of Python 3.11+ was resolved. (Github issue https://github.com/cython/cython/issues/7503)

• Unicode predicates like .isdigit() are now allowed to fail in the Limited API. (Github issue https://github.com/cython/cython/issues/7602)

• Conditional expressions mixing Python float and int object types could accidentally infer float as the common result type, instead of treating both independently.

• Using sizeof() in the size declarations of extern arrays failed. (Github issue https://github.com/cython/cython/issues/7451)

• Enabling profiling generated invalid C code for non-Python return tuples. (Github issue https://github.com/cython/cython/issues/7580)

• abs() on C long long values could generate invalid C code.

• When the CYTHON_AVOID_BORROWED_REFS C macro is enabled, e.g. in GraalPython, dict iteration could fail to compile. Patch by Michael Šimáček. (Github issue https://github.com/cython/cython/issues/7631)

• A C compiler warning about unused functions was resolved. (Github issue https://github.com/cython/cython/issues/7560)

• The py_safe_call_once() C++ mutex helper function in libcpp.mutex failed to compile. (Github issue https://github.com/cython/cython/issues/7585)

• The cpython.array declarations were adapted for Python 3.15. Direct access to the C struct of the array.array data type might require user code changes. (Github issue https://github.com/cython/cython/issues/7659)

• Spaces in file paths written to the depfile were not escaped. Patch by Loïc Estève. (Github issue https://github.com/cython/cython/issues/7423)

• Cython’s cache failed to restore multi-file results. (Github issue https://github.com/cython/cython/issues/7559)

• Using Tempita from its command line failed with a name error. (Github issue https://github.com/cython/cython/issues/7567)

Other changes

• The known builtin types were updated for Py3.15.