# Building C and C++ Extensions {#building}

A C extension for CPython is a shared library (for example, a `.so` file on Linux, `.pyd` on Windows), which exports an *initialization function*.

See `extension-modules`{.interpreted-text role="ref"} for details.

## Building C and C++ Extensions with setuptools[]{#install-index} {#setuptools-index}

Building, packaging and distributing extension modules is best done with third-party tools, and is out of scope of this document. One suitable tool is Setuptools, whose documentation can be found at <https://setuptools.pypa.io/en/latest/setuptools.html>.

The `distutils`{.interpreted-text role="mod"} module, which was included in the standard library until Python 3.12, is now maintained as part of Setuptools.