问题描述

我正在编写一个链接 C++ 库的 Python 扩展，我正在使用 cmake 来帮助构建过程.这意味着现在，我知道如何捆绑它的唯一方法，我必须先用 cmake 编译它们，然后才能运行 setup.py bdist_wheel.一定有更好的方法.

I'm writing a Python extension that links a C++ library and I'm using cmake to help with the build process. This means that right now, the only way I know how to bundle it, I have to first compile them with cmake before I can run setup.py bdist_wheel. There must be a better way.

我想知道是否有可能(或有人尝试过)在 setup.py ext_modules 构建过程中调用 CMake?我猜有一种方法可以创建某个东西的子类，但我不确定在哪里看.

I was wondering if it's possible (or anybody has tried) to invoke CMake as part of the setup.py ext_modules build process? I'm guessing there is a way to create a subclass of something but I'm not sure where to look.

我使用 CMake 是因为它给了我更多的控制权，可以完全按照我的需要使用复杂的构建步骤构建 c 和 c++ 库扩展.另外，我可以使用 findPythonLibs.cmake 中的 PYTHON_ADD_MODULE() 命令直接使用 cmake 轻松构建 Python 扩展.我只是希望这只是一步.

I'm using CMake because it gives me so much more control for building c and c++ libraries extensions with complex build steps exactly as I want it. Plus, I can easily build Python extensions directly with cmake with the PYTHON_ADD_MODULE() command in the findPythonLibs.cmake. I just wish this was all one step.

推荐答案

您基本上需要做的是覆盖 setup.py 中的 build_ext 命令类和在命令类中注册它.在您的 build_ext 自定义实现中，配置并调用 cmake 来配置和构建扩展模块.不幸的是，官方文档对于如何实现自定义 distutils 命令相当简洁(参见 扩展 Distutils);我发现直接研究命令代码更有帮助.例如，这里是 的源代码build_ext 命令.

What you basically need to do is to override the build_ext command class in your setup.py and register it in the command classes. In your custom impl of build_ext, configure and call cmake to configure and then build the extension modules. Unfortunately, the official docs are rather laconic about how to implement custom distutils commands (see Extending Distutils); I find it much more helpful to study the commands code directly. For example, here is the source code for the build_ext command.

我准备了一个简单的项目，由一个 C 扩展 foo 和一个 python 模块 spam.eggs 组成:

I have prepared a simple project consisting out of a single C extension foo and a python module spam.eggs:

so-42585210/
├── spam
│   ├── __init__.py  # empty
│   ├── eggs.py
│   ├── foo.c
│   └── foo.h
├── CMakeLists.txt
└── setup.py

用于测试设置的文件

这些只是我为测试设置脚本而编写的一些简单存根.

Files for testing the setup

These are just some simple stubs I wrote to test the setup script.

spam/eggs.py(仅用于测试库调用):

spam/eggs.py (only for testing the library calls):

from ctypes import cdll
import pathlib


def wrap_bar():
    foo = cdll.LoadLibrary(str(pathlib.Path(__file__).with_name('libfoo.dylib')))
    return foo.bar()

spam/foo.c:

#include "foo.h"

int bar() {
    return 42;
}

spam/foo.h:

#ifndef __FOO_H__
#define __FOO_H__

int bar();

#endif

CMakeLists.txt:

cmake_minimum_required(VERSION 3.10.1)
project(spam)
set(src "spam")
set(foo_src "spam/foo.c")
add_library(foo SHARED ${foo_src})

设置脚本

这就是魔法发生的地方.当然，还有很大的改进空间 - 如果需要，您可以将其他选项传递给 CMakeExtension 类(有关扩展的更多信息，请参阅 构建 C 和 C++ 扩展)，通过覆盖方法 setup.cfg 使 CMake 选项可配置 initialize_options 和 finalize_options 等

Setup script

This is where the magic happens. Of course, there is a lot of room for improvements - you could pass additional options to CMakeExtension class if you need to (for more info on the extensions, see Building C and C++ Extensions), make the CMake options configurable via setup.cfg by overriding methods initialize_options and finalize_options etc.

import os
import pathlib

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


class CMakeExtension(Extension):

    def __init__(self, name):
        # don't invoke the original build_ext for this special extension
        super().__init__(name, sources=[])


class build_ext(build_ext_orig):

    def run(self):
        for ext in self.extensions:
            self.build_cmake(ext)
        super().run()

    def build_cmake(self, ext):
        cwd = pathlib.Path().absolute()

        # these dirs will be created in build_py, so if you don't have
        # any python sources to bundle, the dirs will be missing
        build_temp = pathlib.Path(self.build_temp)
        build_temp.mkdir(parents=True, exist_ok=True)
        extdir = pathlib.Path(self.get_ext_fullpath(ext.name))
        extdir.mkdir(parents=True, exist_ok=True)

        # example of cmake args
        config = 'Debug' if self.debug else 'Release'
        cmake_args = [
            '-DCMAKE_LIBRARY_OUTPUT_DIRECTORY=' + str(extdir.parent.absolute()),
            '-DCMAKE_BUILD_TYPE=' + config
        ]

        # example of build args
        build_args = [
            '--config', config,
            '--', '-j4'
        ]

        os.chdir(str(build_temp))
        self.spawn(['cmake', str(cwd)] + cmake_args)
        if not self.dry_run:
            self.spawn(['cmake', '--build', '.'] + build_args)
        # Troubleshooting: if fail on line above then delete all possible 
        # temporary CMake files including "CMakeCache.txt" in top level dir.
        os.chdir(str(cwd))


setup(
    name='spam',
    version='0.1',
    packages=['spam'],
    ext_modules=[CMakeExtension('spam/foo')],
    cmdclass={
        'build_ext': build_ext,
    }
)

测试

构建项目的轮子，安装它.测试库是否安装:

Testing

Build the project's wheel, install it. Test the library is installed:

$ pip show -f spam
Name: spam
Version: 0.1
Summary: UNKNOWN
Home-page: UNKNOWN
Author: UNKNOWN
Author-email: UNKNOWN
License: UNKNOWN
Location: /Users/hoefling/.virtualenvs/stackoverflow/lib/python3.6/site-packages
Requires: 
Files:
  spam-0.1.dist-info/DESCRIPTION.rst
  spam-0.1.dist-info/INSTALLER
  spam-0.1.dist-info/METADATA
  spam-0.1.dist-info/RECORD
  spam-0.1.dist-info/WHEEL
  spam-0.1.dist-info/metadata.json
  spam-0.1.dist-info/top_level.txt
  spam/__init__.py
  spam/__pycache__/__init__.cpython-36.pyc
  spam/__pycache__/eggs.cpython-36.pyc
  spam/eggs.py
  spam/libfoo.dylib

从 spam.eggs 模块运行包装函数:

Run the wrapper function from spam.eggs module:

$ python -c "from spam import eggs; print(eggs.wrap_bar())"
42

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