144 lines
5.3 KiB
TeX
144 lines
5.3 KiB
TeX
\chapter{Building C and \Cpp{} Extensions with distutils
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\label{building}}
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\sectionauthor{Martin v. L\"owis}{martin@v.loewis.de}
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Starting in Python 1.4, Python provides, on \UNIX{}, a special make
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file for building make files for building dynamically-linked
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extensions and custom interpreters. Starting with Python 2.0, this
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mechanism (known as related to Makefile.pre.in, and Setup files) is no
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longer supported. Building custom interpreters was rarely used, and
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extension modules can be built using distutils.
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Building an extension module using distutils requires that distutils
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is installed on the build machine, which is included in Python 2.x and
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available separately for Python 1.5. Since distutils also supports
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creation of binary packages, users don't necessarily need a compiler
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and distutils to install the extension.
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A distutils package contains a driver script, \file{setup.py}. This is
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a plain Python file, which, in the most simple case, could look like
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this:
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\begin{verbatim}
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from distutils.core import setup, Extension
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module1 = Extension('demo',
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sources = ['demo.c'])
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setup (name = 'PackageName',
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version = '1.0',
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description = 'This is a demo package',
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ext_modules = [module1])
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\end{verbatim}
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With this \file{setup.py}, and a file \file{demo.c}, running
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\begin{verbatim}
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python setup.py build
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\end{verbatim}
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will compile \file{demo.c}, and produce an extension module named
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\samp{demo} in the \file{build} directory. Depending on the system,
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the module file will end up in a subdirectory \file{build/lib.system},
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and may have a name like \file{demo.so} or \file{demo.pyd}.
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In the \file{setup.py}, all execution is performed by calling the
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\samp{setup} function. This takes a variable number of keyword
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arguments, of which the example above uses only a
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subset. Specifically, the example specifies meta-information to build
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packages, and it specifies the contents of the package. Normally, a
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package will contain of addition modules, like Python source modules,
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documentation, subpackages, etc. Please refer to the distutils
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documentation in \citetitle[../dist/dist.html]{Distributing Python
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Modules} to learn more about the features of distutils; this section
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explains building extension modules only.
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It is common to pre-compute arguments to \function{setup}, to better
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structure the driver script. In the example above,
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the\samp{ext_modules} argument to \function{setup} is a list of
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extension modules, each of which is an instance of the
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\class{Extension}. In the example, the instance defines an extension
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named \samp{demo} which is build by compiling a single source file,
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\file{demo.c}.
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In many cases, building an extension is more complex, since additional
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preprocessor defines and libraries may be needed. This is demonstrated
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in the example below.
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\begin{verbatim}
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from distutils.core import setup, Extension
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module1 = Extension('demo',
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define_macros = [('MAJOR_VERSION', '1'),
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('MINOR_VERSION', '0')],
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include_dirs = ['/usr/local/include'],
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libraries = ['tcl83'],
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library_dirs = ['/usr/local/lib'],
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sources = ['demo.c'])
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setup (name = 'PackageName',
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version = '1.0',
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description = 'This is a demo package',
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author = 'Martin v. Loewis',
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author_email = 'martin@v.loewis.de',
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url = 'http://www.python.org/doc/current/ext/building.html',
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long_description = '''
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This is really just a demo package.
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''',
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ext_modules = [module1])
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\end{verbatim}
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In this example, \function{setup} is called with additional
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meta-information, which is recommended when distribution packages have
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to be built. For the extension itself, it specifies preprocessor
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defines, include directories, library directories, and libraries.
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Depending on the compiler, distutils passes this information in
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different ways to the compiler. For example, on \UNIX{}, this may
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result in the compilation commands
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\begin{verbatim}
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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
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gcc -shared build/temp.linux-i686-2.2/demo.o -L/usr/local/lib -ltcl83 -o build/lib.linux-i686-2.2/demo.so
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\end{verbatim}
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These lines are for demonstration purposes only; distutils users
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should trust that distutils gets the invocations right.
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\section{Distributing your extension modules
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\label{distributing}}
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When an extension has been successfully build, there are three ways to
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use it.
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End-users will typically want to install the module, they do so by
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running
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\begin{verbatim}
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python setup.py install
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\end{verbatim}
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Module maintainers should produce source packages; to do so, they run
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\begin{verbatim}
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python setup.py sdist
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\end{verbatim}
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In some cases, additional files need to be included in a source
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distribution; this is done through a \file{MANIFEST.in} file; see the
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distutils documentation for details.
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If the source distribution has been build successfully, maintainers
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can also create binary distributions. Depending on the platform, one
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of the following commands can be used to do so.
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\begin{verbatim}
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python setup.py bdist_wininst
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python setup.py bdist_rpm
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python setup.py bdist_dumb
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\end{verbatim}
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