# 4. C および C++ 拡張のビルド

CPython の C 拡張は 初期化関数 をエクスポートした共有ライブラリ (例、 Linux の `.so` ファイルや Windows の `.pyd` ファイル) です。

To be importable, the shared library must be available on `PYTHONPATH`, and must be named after the module name, with an appropriate extension. When using distutils, the correct filename is generated automatically.

初期化関数のシグネチャは次のとおりです:

PyObject *PyInit_modulename(void)

この関数は完全に初期化されたモジュールか、 `PyModuleDef` インスタンスを返します。 詳しいことは Cモジュールの初期化 を参照してください。

名前にASCIIしか使っていないモジュールの場合、関数名は `PyInit_<modulename>` の `<modulename>` をモジュール名で置き換えたものでなければなりません。 多段階初期化 を使っているときは、モジュール名にASCII以外の文字も使えます。 この場合、初期化関数の名前は `PyInitU_<modulename>` で、 `<modulename>` はハイフンをアンダースコアで置き換えて Python の punycode エンコーディングでエンコードしたものになります。 Python で書くと次のような処理になります:

    def initfunc_name(name):
        try:
            suffix = b'_' + name.encode('ascii')
        except UnicodeEncodeError:
            suffix = b'U_' + name.encode('punycode').replace(b'-', b'_')
        return b'PyInit' + suffix

1つの共有ライブラリに複数の初期化関数を定義することで、複数のモジュールをエクスポートすることは可能です。 しかし、デフォルトではファイル名に対応した関数しか見付けようとしないので、複数のモジュールをインポートさせるにはシンボリックリンクか独自のインポーターを使う必要があります。 詳しいことは PEP 489 の "Multiple modules in one library" 節を参照してください。

## 4.1. Building C and C++ Extensions with distutils

Extension modules can be built using distutils, which is included in Python. Since distutils also supports creation of binary packages, users don't necessarily need a compiler and distutils to install the extension.

A distutils package contains a driver script, `setup.py`. This is a plain Python file, which, in the most simple case, could look like this:

    from distutils.core import setup, Extension

    module1 = Extension('demo',
                        sources = ['demo.c'])

    setup (name = 'PackageName',
           version = '1.0',
           description = 'This is a demo package',
           ext_modules = [module1])

With this `setup.py`, and a file `demo.c`, running

    python setup.py build

will compile `demo.c`, and produce an extension module named `demo` in the `build` directory. Depending on the system, the module file will end up in a subdirectory `build/lib.system`, and may have a name like `demo.so` or `demo.pyd`.

In the `setup.py`, all execution is performed by calling the `setup` function. This takes a variable number of keyword arguments, of which the example above uses only a subset. Specifically, the example specifies meta-information to build packages, and it specifies the contents of the package. Normally, a package will contain additional modules, like Python source modules, documentation, subpackages, etc. Please refer to the distutils documentation in Python モジュールの配布 (レガシーバージョン) to learn more about the features of distutils; this section explains building extension modules only.

It is common to pre-compute arguments to `setup()`, to better structure the driver script. In the example above, the `ext_modules` argument to `setup()` is a list of extension modules, each of which is an instance of the `Extension`. In the example, the instance defines an extension named `demo` which is build by compiling a single source file, `demo.c`.

In many cases, building an extension is more complex, since additional preprocessor defines and libraries may be needed. This is demonstrated in the example below.

    from distutils.core import setup, Extension

    module1 = Extension('demo',
                        define_macros = [('MAJOR_VERSION', '1'),
                                         ('MINOR_VERSION', '0')],
                        include_dirs = ['/usr/local/include'],
                        libraries = ['tcl83'],
                        library_dirs = ['/usr/local/lib'],
                        sources = ['demo.c'])

    setup (name = 'PackageName',
           version = '1.0',
           description = 'This is a demo package',
           author = 'Martin v. Loewis',
           author_email = 'martin@v.loewis.de',
           url = 'https://docs.python.org/extending/building',
           long_description = '''
    This is really just a demo package.
    ''',
           ext_modules = [module1])

In this example, `setup()` is called with additional meta-information, which is recommended when distribution packages have to be built. For the extension itself, it specifies preprocessor defines, include directories, library directories, and libraries. Depending on the compiler, distutils passes this information in different ways to the compiler. For example, on Unix, this may result in the compilation commands

    gcc -DNDEBUG -g -O3 -Wall -Wstrict-prototypes -fPIC -DMAJOR_VERSION=1 -DMINOR_VERSION=0 -I/usr/local/include -I/usr/local/include/python2.2 -c demo.c -o build/temp.linux-i686-2.2/demo.o

    gcc -shared build/temp.linux-i686-2.2/demo.o -L/usr/local/lib -ltcl83 -o build/lib.linux-i686-2.2/demo.so

These lines are for demonstration purposes only; distutils users should trust that distutils gets the invocations right.

## 4.2. Distributing your extension modules

When an extension has been successfully built, there are three ways to use it.

End-users will typically want to install the module, they do so by running

    python setup.py install

Module maintainers should produce source packages; to do so, they run

    python setup.py sdist

In some cases, additional files need to be included in a source distribution; this is done through a `MANIFEST.in` file; see 配布するファイルを指定する for details.

If the source distribution has been built successfully, maintainers can also create binary distributions. Depending on the platform, one of the following commands can be used to do so.

    python setup.py bdist_rpm
    python setup.py bdist_dumb