3. Building C and C++ Extensions with distutils
***********************************************

Starting in Python 1.4, Python provides, on Unix, a special make file
for building make files for building dynamically-linked extensions and
custom interpreters.  Starting with Python 2.0, this mechanism (known
as related to Makefile.pre.in, and Setup files) is no longer
supported. Building custom interpreters was rarely used, and extension
modules can be built using distutils.

Building an extension module using distutils requires that distutils
is installed on the build machine, which is included in Python 2.x and
available separately for Python 1.5. 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 of addition
modules, like Python source modules, documentation, subpackages, etc.
Please refer to the distutils documentation in Distributing Python
Modules (Legacy version) 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.


3.1. Distributing your extension modules
========================================

When an extension has been successfully build, 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 the
distutils documentation for details.

If the source distribution has been build 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_wininst
   python setup.py bdist_rpm
   python setup.py bdist_dumb
