Python C++ extension

A template for a standalone C++ library with dependencies managed by vcpkg accessible through Python using pybind11.

Why should I use this template?

• You want to write a C++ library that can be accessed through Python.
• You want to use cmake to build your C++ code.
• You want to use pybind11 to expose your C++ library as a Python module.
• You want to use some C++ dependencies and manage them with vcpkg. Otherwise you should check other scikit-build sample projects.
• You are not specially concerned about build and install optimizations, it is not a problem if they are long running.

If you want to distribute your extension using pip or conda and you mind that your users take a long time to install it, then it might be better to distribute some built binaries instead of optimizing the build process. This template might still be useful for you as it has a CD workflow for building python wheels with cibuildwheel and uploading them to PyPI.

Example usage

Create a clean Python virtual environment

python -m venv venv

Activate it on Windows

.\venv\Scripts\activate

otherwise

source ./venv/bin/activate

Install this project

pip install git+https://github.com/esdandreu/python-extension-cpp

It will take a while to build as it will build the C++ dependencies as well, but it will work. It is definitely not the most optimal way of installing a package as we are installing as well the vcpkg package manager and building from source dependencies that might as well be installed on the system. But this allows a fast development environment where adding or removing C++ dependencies should be easy.

Alternatively, you can install the package from the binaries distributed in PyPI using the continuous deployment workflow.

pip install example-python-extension-cpp

Test that the C++ code is working in the Python package

Our simple project contains a add function that adds two numbers together.

python -c "import my_python_api; print(my_python_api.add(1, 2))"

It also makes use of the C++ library fftw3 that is available through vcpkg

in order to perform a Fast Fourier Transform over a generated signal, printing its results.

python -c "import my_python_api; my_python_api.hello_fft()"

Setup

Install the requirements

Install vcpkg requirements with the addition of cmake and Python. It could be summarized as:

• git
• Build tools (Visual Studio on Windows or gcc on Linux for example)
• cmake
• Python. Make sure to have development tools installed (python3.X-dev on Linux, being X your version of Python).

If running on a clean linux environment (like a container or Windows Subsystem for Linux) you will need to install some additional tools as it is stated in vcpkg .

sudo apt-get install build-essential curl zip unzip tar pkg-config libssl-dev python3-dev

CMake

Follow the official instructions.

The required cmake version is quite high, if you are using a Linux distribution and installing cmake from the repositories take into account that they might not be updated to the latest version. However there are options to install the latest version of cmake from the command line.

Make sure that when you run cmake --version the output is 3.21 or higher. The reason for this is that we are using some of the 3.21 features to install runtime dependencies (managed with vcpkg ) together with our project so they are available to Python when using its API.

Formatters

This project uses clang-format to format the C++ code. There is a .clang-format file with options that I personally like. Download clang-format as part of LLVM from the official release page.

I als recommend using yapf to format python code.

Clone this repository with vcpkg

Cone this repository with vcpkg as a submodule and navigate into it.

git clone --recursive git@github.com:esdandreu/python-extension-cpp.git
cd python-extension-cpp

Bootstrap vcpkg in Windows. Make sure you have installed the prerequisites.

.\vcpkg\bootstrap-vcpkg.bat

Or in Linux/MacOS. Make sure you have installed developer tools

./vcpkg/bootstrap-vcpkg.sh

Building

Build locally with CMake

Navigate to the root of the repository and create a build directory.

mkdir build

Configure cmake to use vcpkg .

cmake -B build -S . -DCMAKE_TOOLCHAIN_FILE="$pwd/vcpkg/scripts/buildsystems/vcpkg.cmake"

Build the project.

cmake --build build

Build locally with Python

It is recommended to use a clean virtual environment.

scikit-build is required before running the installer, as it is the package that takes care of the installation. The rest of dependencies will be installed automatically.

pip install scikit-build git

Install the repository. By adding [test] to our install command we can install additionally the test dependencies.

pip install .[test]

Testing

Test the C++ library with Google Test

ctest --test-dir build

Test the python extension

pytest

CI/CD

This template contains a continuous integration workflow that builds and tests the C++ library and the python extension ci.yml.

It also contains a continuous deployment workflow that builds wheels and source distributions for the python extension, then creates a github release with it and uploads it to PyPI: cd.yml. That workflow requires a repository secret named PYPI_TOKEN with a PyPI API token. is activated when pushing a version tag to the repository:

git tag -a v0.0.1 -m "First release"
git push origin --tags