py-build-cmake

A modern, PEP 517 compliant build backend for creating Python packages with extensions built using CMake.

In short, the task of a build backend is to make your Python project pip installable. For Python projects that incorporate native code, this may include compilation or other build steps, which often require the invocation of tools like CMake.
Specifically, py-build-cmake performs the following tasks:

1. It reads the project metadata and configuration options from the standard pyproject.toml file of your Python project.
2. It creates source distributions (sdists) of your project that can be shared with others (e.g. by uploading them to PyPI).
3. It drives the CMake build process (e.g. for compiling extension modules written in C or C++) and bundles the results into a Wheel package that can be pip installed by others.

Features

• Building and packaging C, C++ or Fortran extension modules for Python using CMake
• Declarative configuration using pyproject.toml (PEP 621)
• Editable/development installations for Python modules (PEP 660)
• Easy integration with pybind11, nanobind and SWIG, with stable ABI support
• Stub generation for type checking and autocompletion
• Customizable CMake configuration, build, and installation options
• Support for installation of multiple configurations and components, across different Wheel packages
• First-class cross-compilation support
• Reproducible Wheels and source distributions
• No dependency on setuptools
• Compatible with cibuildwheel for building Wheels

Installation

The py-build-cmake package is available on PyPI:

pip install py-build-cmake

Documentation

The documentation can be found on https://tttapa.github.io/py-build-cmake.

A quick start guide is available on the First Steps page. It goes over the recommended file structure, and discusses a basic configuration.
More detailed examples can be found on the Examples page

The format of the pyproject.toml configuration file is explained in the Reference.
Alternatively, use the command-line interface to get the documentation for all supported options:

py-build-cmake config format

Usage

If you don't have one already, add a pyproject.toml configuration file to your project's repository. Specify the mandatory project metadata (PyPA: Declaring project metadata), and tell py-build-cmake how to build your CMake project. For example:

[project] # Project metadata
name = "example-project"
requires-python = ">=3.8"
readme = "README.md"
license = "MIT"
license-files = ["LICENSE"]
dependencies = ["numpy"]
dynamic = ["version", "description"]

[build-system] # How pip and other frontends should build this project
requires = ["py-build-cmake~=0.6.0a4"]
build-backend = "py_build_cmake.build"

[tool.py-build-cmake.module] # Where to find the Python module to package
directory = "src-python"

[tool.py-build-cmake.sdist] # What to include in source distributions
include = ["CMakeLists.txt", "src/*"]

[tool.py-build-cmake.cmake] # How to build the CMake project
build_type = "RelWithDebInfo"
source_path = "src"
build_args = ["-j"]
install_components = ["python_modules"]

[tool.py-build-cmake.stubgen] # Whether and how to generate typed stub files

The README of examples/minimal describes this configuration file in much more detail.

Then use pip, build or another PEP 517 compatible frontend to build and/or install the package.

Build sdist and wheel packages you can upload to PyPI:

python -m pip install -U build
python -m build . # find the sdist and wheel file in the 'dist' folder

Install the package in the current environment:

pip install .    # normal installation
pip install -e . # editable installation

Examples

As an introduction to py-build-cmake, see examples/minimal for a detailed overview of the configuration files and the directory structure, using a very simple Python module as an example.
For a more advanced, real-world example, see examples/pybind11-project and examples/nanobind-project.
Alternatively, SWIG can also be used instead of pybind11 or nanobind, as demonstrated in examples/swig-project.
If you are interested in packaging C/C++/Fortran programs using py-build-cmake, have a look at examples/minimal-program.
See the examples folder for a full list of examples.

A full example that uses the Conan package manager for C++ dependencies, and that uses GitHub Actions to deploy the Wheel packages built by py-build-cmake to PyPI can be found in tttapa/py-build-cmake-example.

Projects using py-build-cmake

If you need more examples, you can look at the following projects using py-build-cmake as their Python build backend:

• alpaqa
• QPALM

Alternatives and related tools

• scikit-build-core: alternative CMake build backend, successor of scikit-build
• meson-python: Meson build backend
• flit: pure-Python packaging tool and build backend
• hatchling: build backend of the Hatch project manager, supports build hooks
• poetry-core: pure-Python build backend for the Poetry package manager
• crossenv: tool to trick setuptools into cross-compiling by monkey patching the sysconfig and distutils modules