setup.py

"""
This is a setup.py file for building the C extension using CMake.
It is modified from the pybind11 example:
https://github.com/pybind/cmake_example
"""

import os
import subprocess
import sys
from pathlib import Path

from setuptools import Extension, setup
from setuptools.command.build_ext import build_ext


# A CMakeExtension needs a sourcedir instead of a file list.
# The name must be the _single_ output extension from the CMake build.
# If you need multiple extensions, see scikit-build.
class CMakeExtension(Extension):
    def __init__(self, name: str, sourcedir: str = "") -> None:
        super().__init__(name, sources=[])
        self.sourcedir = os.fspath(Path(sourcedir).resolve())


class CMakeBuild(build_ext):
    def build_extension(self, ext: CMakeExtension) -> None:
        # Must be in this form due to bug in .resolve() only fixed in Python 3.10+
        ext_fullpath = Path.cwd() / self.get_ext_fullpath(ext.name)
        extdir = ext_fullpath.parent.resolve()

        # Using this requires trailing slash for auto-detection & inclusion of
        # auxiliary "native" libs

        debug = int(os.environ.get("DEBUG", 0)) if self.debug is None else self.debug
        cfg = "Debug" if debug else "Release"

        # CMake lets you override the generator - we need to check this.
        # Can be set with Conda-Build, for example.
        cmake_generator = os.environ.get("CMAKE_GENERATOR", "")

        # Set Python_EXECUTABLE instead if you use PYBIND11_FINDPYTHON
        # EXAMPLE_VERSION_INFO shows you how to pass a value into the C++ code
        # from Python.
        cmake_args = [
            f"-DCMAKE_LIBRARY_OUTPUT_DIRECTORY={extdir}{os.sep}",
            f"-DPYTHON_EXECUTABLE={sys.executable}",
            f"-DCMAKE_BUILD_TYPE={cfg}",  # not used on MSVC, but no harm
        ]
        build_args = []
        # Adding CMake arguments set as environment variable
        # (needed e.g. to build for ARM OSx on conda-forge)
        if "CMAKE_ARGS" in os.environ:
            cmake_args += [item for item in os.environ["CMAKE_ARGS"].split(" ") if item]

        cmake_args += [f"-DVERSION_INFO={self.distribution.get_version()}"]

        build_temp = Path(self.build_temp) / ext.name
        if not build_temp.exists():
            build_temp.mkdir(parents=True)

        subprocess.run(
            ["cmake", ext.sourcedir, *cmake_args], cwd=build_temp, check=True
        )
        subprocess.run(
            ["cmake", "--build", ".", *build_args], cwd=build_temp, check=True
        )


# The information here can also be placed in setup.cfg - better separation of
# logic and declaration, and simpler if you include description/version in a file.
skip_cmake = os.environ.get("SKIP_CMAKE", "0") == "1"
if skip_cmake:
    ext_modules = []
else:
    ext_modules = [CMakeExtension("grav_sim", sourcedir="")]

setup(
    packages=["grav_sim"],
    ext_modules=ext_modules,
    cmdclass={"build_ext": CMakeBuild},
    package_data={"": ["src/*"]},
    include_package_data=True,
    zip_safe=False,
)