Compilation with Scikit-Build

Scikit-Build is building system generator based on Python’s setpuptools system and C++’s Cmake system. With Scikit-Build toolkit, we can compile C++/Python hybrid libraries automatically. The minimum requirements of Scikit-Build include three files: setup.py, pyproject.toml and CMakeLists.txt.

setup.py

setup.py is config file used by Python’s setuptools. It consists of basic information about the project. To activate Sckikit-Build tools, the setup function must be overloaded by function provided by Scikit-Build in setup.py:

from skbuild import setup

An example of setup.py can be found here. The additional options in setup.py are listed on Scikit-Build’s website and Python’s document.

pyproject.toml

pyproject.toml is the specified file format of PEP 518, which contains the dependencies of the project. A detailed description of pyproject.toml can be found in pip’s document. Here, we only utilize a simplified yet practical version that is suitable for most scenarios:

[build-system]
requires = [
    "setuptools>=42",
    "cmake>=3.13",
    "scikit-build>=0.14.1",
    "pybind11>=2.9.2",
]

build-backend = "setuptools.build_meta"

CMakeLists.txt

CMakeLists.txt file contains building options of CMake. To correctly build a pybind11 project, the location of pybind11 must be provided to CMake:

# add package: pybind11
execute_process(
    COMMAND "${Python3_EXECUTABLE}" -c
            "import pybind11; print(pybind11.get_cmake_dir())"
    OUTPUT_VARIABLE pybind11_dir
    OUTPUT_STRIP_TRAILING_WHITESPACE COMMAND_ECHO STDOUT)
find_package(pybind11 CONFIG REQUIRED PATHS ${pybind11_dir})

To compile a C++ source code into a shared library, we can use the following commands:

pybind11_add_module(example_cpp_lib src/example_lib/example.cpp)

install(TARGETS example_cpp_lib DESTINATION .)

The pybind11_add_module command will compile example.cpp file into shared library named example_cpp_lib. And when the project is packaged by Python, install command will place the library in the root directory of the project. This example CMakeLists.txt can be found here.

Building

Once these three things are prepared correctly. In root directory of the project, we can utilize commands provided by setuptools to build the package.

python3 setup.py build
python3 setup.py install

The command build will build and package the project into a directory named _skbuild, and install command will copy the packaged project to site-packages directory of Python.