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.. highlight:: c
.. _building:
*****************************
Building C and C++ Extensions
*****************************
A C extension for CPython is a shared library (e.g. a ``.so`` file on Linux,
``.pyd`` on Windows), which exports an *initialization function*.
To be importable, the shared library must be available on :envvar:`PYTHONPATH`,
and must be named after the module name, with an appropriate extension.
When using setuptools, the correct filename is generated automatically.
The initialization function has the signature:
.. c:function:: PyObject* PyInit_modulename(void)
It returns either a fully initialized module, or a :c:type:`PyModuleDef`
instance. See :ref:`initializing-modules` for details.
.. highlight:: python
For modules with ASCII-only names, the function must be named
``PyInit_<modulename>``, with ``<modulename>`` replaced by the name of the
module. When using :ref:`multi-phase-initialization`, non-ASCII module names
are allowed. In this case, the initialization function name is
``PyInitU_<modulename>``, with ``<modulename>`` encoded using Python's
*punycode* encoding with hyphens replaced by underscores. In Python::
def initfunc_name(name):
try:
suffix = b'_' + name.encode('ascii')
except UnicodeEncodeError:
suffix = b'U_' + name.encode('punycode').replace(b'-', b'_')
return b'PyInit' + suffix
It is possible to export multiple modules from a single shared library by
defining multiple initialization functions. However, importing them requires
using symbolic links or a custom importer, because by default only the
function corresponding to the filename is found.
See the *"Multiple modules in one library"* section in :pep:`489` for details.
.. highlight:: c
.. _setuptools-index:
Building C and C++ Extensions with setuptools
=============================================
Python 3.12 and newer no longer come with distutils. Please refer to the
``setuptools`` documentation at
https://setuptools.readthedocs.io/en/latest/setuptools.html
to learn more about how build and distribute C/C++ extensions with setuptools.
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