在Windows中构建Python C扩展时导出符号时出错

Question

我正在努力将Python模块移植到Windows.我有一个玩具示例如下.

文件夹结构是:

foo/
  libfoo/
    foo.c
  setup.py

setup.py

from setuptools import setup, Extension

sources = ['libfoo/foo.c']

foo = Extension('libfoo',
                 sources = sources,
                 define_macros = None,
                 include_dirs = ['./libfoo'],
                 libraries = None,
                 library_dirs = None,
                 )

setup(name          = 'foo',
      ext_modules      = [foo],
      install_requires = ['setuptools'],
)

libfoo/foo.c(完整性)

#include <stdio.h>

void foo() {
  printf("Hello World!");
}

当我尝试安装包时,遇到错误.

C:\Users\user\foo>python setup.py install
running install
running bdist_egg
running egg_info
creating foo.egg-info
writing requirements to foo.egg-info\requires.txt
writing foo.egg-info\PKG-INFO
writing top-level names to foo.egg-info\top_level.txt
writing dependency_links to foo.egg-info\dependency_links.txt
writing manifest file 'foo.egg-info\SOURCES.txt'
reading manifest file 'foo.egg-info\SOURCES.txt'
writing manifest file 'foo.egg-info\SOURCES.txt'
installing library code to build\bdist.win32\egg
running install_lib
running build_ext
building 'libfoo' extension
creating build
creating build\temp.win32-2.7
creating build\temp.win32-2.7\Release
creating build\temp.win32-2.7\Release\libfoo
c:\Program Files (x86)\Microsoft Visual Studio 9.0\VC\BIN\cl.exe /c /nologo /Ox
/MD /W3 /GS- /DNDEBUG -I./libfoo -IC:\Python27\include -IC:\Python27\PC /Tclibfo
o/foo.c /Fobuild\temp.win32-2.7\Release\libfoo/foo.obj
foo.c
creating build\lib.win32-2.7
c:\Program Files (x86)\Microsoft Visual Studio 9.0\VC\BIN\link.exe /DLL /nologo
/INCREMENTAL:NO /LIBPATH:C:\Python27\libs /LIBPATH:C:\Python27\PCbuild /EXPORT:i
nitlibfoo build\temp.win32-2.7\Release\libfoo/foo.obj /OUT:build\lib.win32-2.7\l
ibfoo.pyd /IMPLIB:build\temp.win32-2.7\Release\libfoo\libfoo.lib /MANIFESTFILE:b
uild\temp.win32-2.7\Release\libfoo\libfoo.pyd.manifest
LINK : error LNK2001: unresolved external symbol initlibfoo
build\temp.win32-2.7\Release\libfoo\libfoo.lib : fatal error LNK1120: 1 unresolv
ed externals
error: command 'c:\\Program Files (x86)\\Microsoft Visual Studio 9.0\\VC\\BIN\\l
ink.exe' failed with exit status 1120

似乎distutils包(在本例中为setuputils)将始终从共享扩展中导出一个符号,即"init + extension_name" [Link].

它在Windows链接器"导出"选项[链接]中指定,但找不到该符号.

救命？

编辑:C代码不使用Python C API,即"#include".这是因为该项目的目标是获取现有的C库并通过Python扩展包含在Python包装器中.该软件包适用于Unix/Linux.

Answer 1

经过大量的游戏,我能够理解这个问题.

解决方案:在Windows中,您必须为扩展定义初始化函数,因为setuptools将构建.pyd文件,而不是DLL

要在Python 2中解决此问题,请initlibfoo()在源中定义方法.

#include <Python.h>

PyMODINIT_FUNC initlibfoo(void) {
    // do stuff...
}

要在Python 3中解决此问题,请PyInit_libfoo()在源中定义方法.

#include <Python.h>

PyMODINIT_FUNC PyInit_libfoo(void) {
    // do stuff...
}

所以现在,foo.c看起来像:

#include <stdio.h>
#include <Python.h>

void foo() {
  printf("Hello World!");
}

PyMODINIT_FUNC initlibfoo(void) // Python 2.7
//PyMODINIT_FUNC PyInit_libfoo(void) // Python 3.5
{
    // do stuff...
}

说明

在为Windows编译Python扩展时,Extension类将告诉链接器为其他要调用的程序导出函数.这可以在终端输出中看到:

c:\Program Files (x86)\Microsoft Visual Studio 9.0\VC\BIN\link.exe /DLL /nologo
/INCREMENTAL:NO /LIBPATH:C:\Python27\libs /LIBPATH:C:\Python27\PCbuild /EXPORT:i
nitlibfoo build\temp.win32-2.7\Release\libfoo/foo.obj /OUT:build\lib.win32-2.7\l
ibfoo.pyd /IMPLIB:build\temp.win32-2.7\Release\libfoo\libfoo.lib /MANIFESTFILE:b
uild\temp.win32-2.7\Release\libfoo\libfoo.pyd.manifest

(强调/EXPORT:initlibfoo)

现在,这是C/C++ Extensions的必需功能,因此可以将它们作为模块导入.换句话说,当你import libfoo将Python initlibfoo作为模块初始化的一部分调用.pyd上的函数时.这里遇到的错误是由于链接器被告知导出函数initlibfoo但是它无法在C对象文件中找到符号,因为它从未在源中定义过!

当然,人们应该能够拒绝出口符号的选择吗？显然不是.回到Extension类文档,有一个参数export_symbols.我尝试传递None给它并且仍在使用链接器选项.似乎没有办法绕过这个链接器选项.

不推荐:如果由于某种原因,需要Python.h困扰你,那就有办法解决这个问题.你仍然需要定义上面的"init"方法,但你可以这样做:

void initlibfoo() {} //Python 2.7
void PyInit_libfoo() {} //Python 3.5

但是现在,您无法使用库import libfoo.您可以使用ctypes模块并加载它ctypes.PyDLL('/path/to/pyd').基本上,您使用Python为您构建DLL,在这种情况下,它会,但它构建一个称为.pyd文件的特殊DLL.然后要使用它,您必须在via ctypes模块中加载它.