# 4. Building C and C++ Extensions

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 Defining extension modules for details.

## 4.1. Building C and C++ Extensions with setuptools

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` module, which was included in the standard library until Python 3.12, is now maintained as part of Setuptools.