Compiling Python to C using setuptools and Cython

plum¹ compiles an ordinary Python file into an extension module (in C) using Cython and setuptools’ Cython integration. It’s the first time I’ve encountered this, so here’s a high-level description of how it works.

In setup.py, pass the ext_modules arg to setup, wrapping an Extension that points to the module you want to compile:

```python hl_lines=‘9’ from setuptools import setup, Extension

setup( # … ext_modules=[Extension(“plum.function”, [“plum/function.py”])], )

`setuptools` has built-in [Cython integration](https://setuptools.pypa.io/en/latest/userguide/ext_modules.html#distributing-extensions-compiled-with-cython). If it finds that Cython is installed, it'll use it to build extensions with `.py` and `.pyx` sources. Including Cython as a build dependency in `pyproject.toml` ensures that it's installed and ready to go:

```toml
[build-system]
requires = [
    # ...
    "cython",
]

What’s a Python extension module?

An extension module is a program written in C (or C++) that uses Python’s C API to hook into Python’s run-time system. Interop works both ways: you can call Python objects from C and vice versa. A common reason for using extensions is improved speed. See the official docs on extension modules for more.

What’s Cython?

Cython is a compiler for compiling programs written in Python and the Cython programming language into C extension modules. I’d recommend the reading through the rather friendly documentation as well.

Footnotes

1. plum is a really cool library that brings Julia-style typed multiple dispatch to Python!