如何在Windows上使用cython编译__init__.py文件 [英] How to compile __init__.py file using cython on Windows

问题描述

当我使用 setup.py build_ext --inplace 命令在Windows上编译任意__init__.py文件时，它具有无法解决的外部符号错误（即LINK：错误LNK2001：无法解析的外部符号PyInit ___ init __）。

When I compile an arbitrary __init__.py file on Windows with setup.py build_ext --inplace command, it has an unresolvable external symbol error (i.e. "LINK : error LNK2001: An unresolvable external symbol PyInit___init__").

本地环境：

python3.7,
Cython 0.29.14,
window10 x64,
Microsoft Visual Studio 2017,

ctest / __ init __。py

ctest/__init__.py

# cython: language_level=3
print('__init__')

setup.py

from distutils.core import setup
from Cython.Build import cythonize


def compile_code(name, filename):
    setup(
        name=name,
        ext_modules=cythonize(filename),
    )


if __name__ == '__main__':
    compile_code('a', 'ctest/__init__.py')

终端打印的信息：

Compiling ctest/__init__.py because it changed.
[1/1] Cythonizing ctest/__init__.py
running build_ext
building 'ctest.__init__' extension
creating build
creating build\temp.win-amd64-3.7
creating build\temp.win-amd64-3.7\Release
creating build\temp.win-amd64-3.7\Release\ctest
C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC\Tools\MSVC\14.16.27023\bin\HostX86\x64\cl.exe /c /nologo /Ox /W3 /GL /DNDEBUG /MD -Id:\py37\include -Id:\py37\incl
ude "-IC:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC\Tools\MSVC\14.16.27023\include" "-IC:\Program Files (x86)\Windows Kits\NETFXSDK\4.6.1\include\um" "-IC:\Pro
gram Files (x86)\Windows Kits\10\include\10.0.18362.0\ucrt" "-IC:\Program Files (x86)\Windows Kits\10\include\10.0.18362.0\shared" "-IC:\Program Files (x86)\Windows Kits\10\includ
e\10.0.18362.0\um" "-IC:\Program Files (x86)\Windows Kits\10\include\10.0.18362.0\winrt" "-IC:\Program Files (x86)\Windows Kits\10\include\10.0.18362.0\cppwinrt" /Tcctest/__init__
.c /Fobuild\temp.win-amd64-3.7\Release\ctest/__init__.obj
__init__.c
C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC\Tools\MSVC\14.16.27023\bin\HostX86\x64\link.exe /nologo /INCREMENTAL:NO /LTCG /DLL /MANIFEST:EMBED,ID=2 /MANIFESTU
AC:NO /LIBPATH:d:\py37\Libs /LIBPATH:D:\ENVS\cpytrantest\libs /LIBPATH:D:\ENVS\cpytrantest\PCbuild\amd64 "/LIBPATH:C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC
\Tools\MSVC\14.16.27023\lib\x64" "/LIBPATH:C:\Program Files (x86)\Windows Kits\NETFXSDK\4.6.1\lib\um\x64" "/LIBPATH:C:\Program Files (x86)\Windows Kits\10\lib\10.0.18362.0\ucrt\x6
4" "/LIBPATH:C:\Program Files (x86)\Windows Kits\10\lib\10.0.18362.0\um\x64" /EXPORT:PyInit___init__ build\temp.win-amd64-3.7\Release\ctest/__init__.obj /OUT:C:\Users\76923\Deskto
p\cpythonrecord\ctest\__init__.cp37-win_amd64.pyd /IMPLIB:build\temp.win-amd64-3.7\Release\ctest\__init__.cp37-win_amd64.lib
LINK : error LNK2001: An unresolvable external symbol PyInit___init__
build\temp.win-amd64-3.7\Release\ctest\__init__.cp37-win_amd64.lib : fatal error LNK1120: An external command that cannot be parsed
error: command 'C:\\Program Files (x86)\\Microsoft Visual Studio\\2017\\Community\\VC\\Tools\\MSVC\\14.16.27023\\bin\\HostX86\\x64\\link.exe' failed with exit status 1120

推荐答案

也许此行为可能被视为 distutils -package中的一个小错误（如@DavidW所指出的那样）是一个未解决的问题： https://bugs.python.org/issue35893 ）。但是，它也表明，对 __ init __。py 进行cythonize / compiling的方法不是很流行，它使用了一些未记录的实现细节，这些细节将来可能会改变，因此这样做可能更明智。避免干预 __ init __。py 。

Maybe this behaviour might be viewed as a small bug in distutils-package (as pointed out by @DavidW there is this open issue: https://bugs.python.org/issue35893). However, it also shows, that cythonizing/compiling __init__.py isn't very popular and uses some undocumented implementation details which might change in the future, so it could be wiser to refrain from meddling with __init__.py.

但是如果您必须...

But if you must...

显式导入软件包时，例如

When a package is imported explicitly, e.g.

import ctest

或隐式，例如

import ctest.something

FileFinder 将看到已导入一个包而不是模块，并且将尝试加载 ctest / __ init __。py 代替 ctest.py 的值（很可能不存在）：

The FileFinder will see that a package, and not a module, is imported and will try to load ctest/__init__.py instead of ctest.py (which most likely doesn't exists):

    # Check if the module is the name of a directory (and thus a package).
    if cache_module in cache:
        base_path = _path_join(self.path, tail_module)
        for suffix, loader_class in self._loaders:
            init_filename = '__init__' + suffix
            full_path = _path_join(base_path, init_filename)
            if _path_isfile(full_path):
                return self._get_spec(loader_class, fullname, full_path, [base_path], target)

使用的后缀loader_class 用于加载 __ init __。so ， __ init __。py 和 __ init __。pyc 的顺序（另请参见SO-post ）。这意味着，如果我们设法创建 __ init __。so 而不是 __ init __。py ，则会加载它。

Used suffix, loader_class are for loading __init__.so, __init__.py and __init__.pyc in this order (see also this SO-post). This means, __init__.so will be loaded instead of __init__.py if we manage to create one.

执行 __ init __。py 时，属性 __ name __ 是包的名称，例如您的情况下的 ctest ，而不是人们认为的 __ init __ 。因此，Python解释器在加载扩展名 __ init __。so 为 PyInit_ctest 时将调用的init函数的名称。在您的情况下（而不是人们可能认为的 PyInit ___ init __ ）。

While __init__.py is executed, The property __name__ is the name of the package, i.e. ctest in your case, and not __init__ as one might think. Thus, the name of the init-function, Python-interpreter will call when loading the extension __init__.so is PyInit_ctest in your case (and not PyInit___init__ as one might think).

以上内容说明了为什么所有这些都不能在Linux上运行盒子。 Windows呢？

The above explains, why it all works on Linux out-of-the-box. What about Windows?

加载程序只能使用so / dll中未被隐藏的符号。默认情况下，所有使用gcc构建的符号都是可见的，但Windows上的VisualStudio则不可见-默认情况下，所有符号都隐藏（请参见例如 SO- post ）。

The loader can only use symbols from a so/dll which aren't hidden. Per default all symbols built with gcc are visible, but not for VisualStudio on Windows - where all symbols are hidden per default (see e.g. this SO-post).

但是，C扩展的init函数必须是可见的（并且只有init函数），因此可以在加载程序的帮助下进行调用-解决方案是在链接时导出该符号（即 PyInit_ctest ），在您的情况下，这是错误的 / EXPORT：PyInit ___ init __ -链接程序的选项。

However, the init-function of a C-extension must be visible (and only the init-function) so it can be called with help of the loader - the solution is to export this symbol (i.e. PyInit_ctest) while linking, in your case it is the wrong /EXPORT:PyInit___init__-option for the linker.

该问题可以在distutils中找到，或更精确的在 build_ext 级：

The problem can be found in distutils, or more precise in build_ext-class:

def get_export_symbols(self, ext):
    """Return the list of symbols that a shared extension has to
    export.  This either uses 'ext.export_symbols' or, if it's not
    provided, "PyInit_" + module_name.  Only relevant on Windows, where
    the .pyd file (DLL) must export the module "PyInit_" function.
    """
    initfunc_name = "PyInit_" + ext.name.split('.')[-1]
    if initfunc_name not in ext.export_symbols:
        ext.export_symbols.append(initfunc_name)
    return ext.export_symbols

在这里，可悲的是 ext.name 具有 __ init __ 。

Here, sadly ext.name has __init__ in it.

从这里开始，一种可能的解决方案很简单：覆盖 get_export_symbols ，即添加跟随您的 setup.py 文件（请阅读以获取更简单的版本）：

From here, one possible solution is easy : to override get_export_symbols, i.e. to add the following to your setup.py-file (read on for a even simpler version):

...
from distutils.command.build_ext import build_ext
def get_export_symbols_fixed(self, ext):
    names = ext.name.split('.')
    if names[-1] != "__init__":
        initfunc_name = "PyInit_" + names[-1]
    else:
        # take name of the package if it is an __init__-file
        initfunc_name = "PyInit_" + names[-2]
    if initfunc_name not in ext.export_symbols:
        ext.export_symbols.append(initfunc_name)
    return ext.export_symbols

# replace wrong version with the fixed:
build_ext.get_export_symbols = get_export_symbols_fixed
...

调用 python setup.py build_ext -i 现在应该足够了（因为 __ init __。so 将被加载，而不是 __ init__ .py ）。

Calling python setup.py build_ext -i should be enough now (because __init__.so will be loaded rather than __init__.py).

但是，正如@DawidW指出的，Cython使用宏 PyMODINIT_FUNC ，已定义as

However, as @DawidW has pointed out, Cython uses macro PyMODINIT_FUNC, which is defined as

#define PyMODINIT_FUNC Py_EXPORTED_SYMBOL PyObject*

带有 Py_EXPORTED_SYMBOL 被标记为在Windows上可见/已导出：

with Py_EXPORTED_SYMBOL being marked as visible/exported on Windows:

#define Py_EXPORTED_SYMBOL __declspec(dllexport)

因此，无需将符号标记为在命令行可见。更糟糕的是，这是警告LNK4197 的原因：

Thus, there is no need to mark the symbol as visible at the command line. Even worse, this is the reason for the warning LNK4197:

__ init __。obj：警告LNK4197：多次指定导出 PyInit_ctest；
使用第一个规范

__init__.obj : warning LNK4197: export 'PyInit_ctest' specified multiple times; using first specification

如 PyInit_test 标记为 __declspec（dllexport）并同时通过选项 / EXPORT：导出。

as PyInit_test is marked as __declspec(dllexport) and exported via option /EXPORT: at the same time.

/ EXPORT： -option将被distutils跳过，如果 export_symbols 为空，我们甚至可以使用更简单的 command.build_ext ：

/EXPORT:-option will be skipped by distutils, if export_symbols is empty, we can use even a simpler version of command.build_ext:

...
from distutils.command.build_ext import build_ext
def get_export_symbols_fixed(self, ext):
    pass  # return [] also does the job!

# replace wrong version with the fixed:
build_ext.get_export_symbols = get_export_symbols_fixed
...

这比第一个版本更好，因为它还修复了警告LNK4197！

This is even better than the first version, as it also fixes warning LNK4197!

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