Introduction

Recently I had to convert a python code base into Cython binaries. Because we are using poetry, it was not straight forward. Here is the process to do it step by step. You can see a sample of a complete working codebase directly here: https://github.com/dhassault/cython_with_poetry

From this point, I assume you have an existing python codebase and you’re using poetry.

Create a build.py

In your root directory, you’re going to create a [build.py](http://build.py) file. This script will replace [setup.py](http://setup.py) that you would normally write with Cython.

The one I’m using for the sample package is the following:

from Cython.Build import cythonize

exclude_list = [
    "sample_package/excluded_module/**",
]
compiler_directives = {"language_level": 3, "embedsignature": True}

def build(setup_kwargs):
    setup_kwargs.update(
        {
            "name": "sample-package",
            "package": ["sample-package"],
            # https://cython.readthedocs.io/en/latest/src/userguide/source_files_and_compilation.html#cythonize-arguments
            "ext_modules": cythonize(
                module_list="sample_package/**/*.py",
                exclude=exclude_list,
                compiler_directives=compiler_directives,
                nthreads=5,
            ),
        }
    )

It’s quite straight forward, I added some useful arguments for the example.

Modify your pyproject.toml

The second step is to modify your pyproject.toml by adding two things:

• In [tool.poetry], add build = "[build.py](http://build.py/)"
• In [build-system] > requires = ["poetry-core>=1.0.0", "setuptools>=62.6.0", "Cython>=0.29.30"] adapted to your codebase

Build

Everything is ready, you just have to install your package as usual: poetry install. You will see different generated files appearing like ....c and ....so .