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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="X-UA-Compatible" content="IE=Edge" /> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <title>4. Building C and C++ Extensions — Python 3.6.7 documentation</title> <link rel="stylesheet" href="../_static/pydoctheme.css" type="text/css" /> <link rel="stylesheet" href="../_static/pygments.css" type="text/css" /> <script type="text/javascript" id="documentation_options" data-url_root="../" src="../_static/documentation_options.js"></script> <script type="text/javascript" src="../_static/jquery.js"></script> <script type="text/javascript" src="../_static/underscore.js"></script> <script type="text/javascript" src="../_static/doctools.js"></script> <script type="text/javascript" src="../_static/sidebar.js"></script> <link rel="search" type="application/opensearchdescription+xml" title="Search within Python 3.6.7 documentation" href="../_static/opensearch.xml"/> <link rel="author" title="About these documents" href="../about.html" /> <link rel="index" title="Index" href="../genindex.html" /> <link rel="search" title="Search" href="../search.html" /> <link rel="copyright" title="Copyright" href="../copyright.html" /> <link rel="next" title="5. Building C and C++ Extensions on Windows" href="windows.html" /> <link rel="prev" title="3. Defining Extension Types: Assorted Topics" href="newtypes.html" /> <link rel="shortcut icon" type="image/png" href="../_static/py.png" /> <link rel="canonical" href="https://docs.python.org/3/extending/building.html" /> <script type="text/javascript" src="../_static/copybutton.js"></script> </head><body> <div class="related" role="navigation" aria-label="related navigation"> <h3>Navigation</h3> <ul> <li class="right" style="margin-right: 10px"> <a href="../genindex.html" title="General Index" accesskey="I">index</a></li> <li class="right" > <a href="../py-modindex.html" title="Python Module Index" >modules</a> |</li> <li class="right" > <a href="windows.html" title="5. Building C and C++ Extensions on Windows" accesskey="N">next</a> |</li> <li class="right" > <a href="newtypes.html" title="3. Defining Extension Types: Assorted Topics" accesskey="P">previous</a> |</li> <li><img src="../_static/py.png" alt="" style="vertical-align: middle; margin-top: -1px"/></li> <li><a href="https://www.python.org/">Python</a> »</li> <li> <a href="../index.html">3.6.7 Documentation</a> » </li> <li class="nav-item nav-item-1"><a href="index.html" accesskey="U">Extending and Embedding the Python Interpreter</a> »</li> <li class="right"> <div class="inline-search" style="display: none" role="search"> <form class="inline-search" action="../search.html" method="get"> <input placeholder="Quick search" type="text" name="q" /> <input type="submit" value="Go" /> <input type="hidden" name="check_keywords" value="yes" /> <input type="hidden" name="area" value="default" /> </form> </div> <script type="text/javascript">$('.inline-search').show(0);</script> | </li> </ul> </div> <div class="document"> <div class="documentwrapper"> <div class="bodywrapper"> <div class="body" role="main"> <div class="section" id="building-c-and-c-extensions"> <span id="building"></span><h1>4. Building C and C++ Extensions<a class="headerlink" href="#building-c-and-c-extensions" title="Permalink to this headline">¶</a></h1> <p>A C extension for CPython is a shared library (e.g. a <code class="docutils literal notranslate"><span class="pre">.so</span></code> file on Linux, <code class="docutils literal notranslate"><span class="pre">.pyd</span></code> on Windows), which exports an <em>initialization function</em>.</p> <p>To be importable, the shared library must be available on <span class="target" id="index-0"></span><a class="reference internal" href="../using/cmdline.html#envvar-PYTHONPATH"><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PYTHONPATH</span></code></a>, and must be named after the module name, with an appropriate extension. When using distutils, the correct filename is generated automatically.</p> <p>The initialization function has the signature:</p> <dl class="function"> <dt id="c.PyInit_modulename"> <a class="reference internal" href="../c-api/structures.html#c.PyObject" title="PyObject">PyObject</a>* <code class="descname">PyInit_modulename</code><span class="sig-paren">(</span>void<span class="sig-paren">)</span><a class="headerlink" href="#c.PyInit_modulename" title="Permalink to this definition">¶</a></dt> <dd></dd></dl> <p>It returns either a fully-initialized module, or a <a class="reference internal" href="../c-api/module.html#c.PyModuleDef" title="PyModuleDef"><code class="xref c c-type docutils literal notranslate"><span class="pre">PyModuleDef</span></code></a> instance. See <a class="reference internal" href="../c-api/module.html#initializing-modules"><span class="std std-ref">Initializing C modules</span></a> for details.</p> <p>For modules with ASCII-only names, the function must be named <code class="docutils literal notranslate"><span class="pre">PyInit_<modulename></span></code>, with <code class="docutils literal notranslate"><span class="pre"><modulename></span></code> replaced by the name of the module. When using <a class="reference internal" href="../c-api/module.html#multi-phase-initialization"><span class="std std-ref">Multi-phase initialization</span></a>, non-ASCII module names are allowed. In this case, the initialization function name is <code class="docutils literal notranslate"><span class="pre">PyInitU_<modulename></span></code>, with <code class="docutils literal notranslate"><span class="pre"><modulename></span></code> encoded using Python’s <em>punycode</em> encoding with hyphens replaced by underscores. In Python:</p> <div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">initfunc_name</span><span class="p">(</span><span class="n">name</span><span class="p">):</span> <span class="k">try</span><span class="p">:</span> <span class="n">suffix</span> <span class="o">=</span> <span class="sa">b</span><span class="s1">'_'</span> <span class="o">+</span> <span class="n">name</span><span class="o">.</span><span class="n">encode</span><span class="p">(</span><span class="s1">'ascii'</span><span class="p">)</span> <span class="k">except</span> <span class="ne">UnicodeEncodeError</span><span class="p">:</span> <span class="n">suffix</span> <span class="o">=</span> <span class="sa">b</span><span class="s1">'U_'</span> <span class="o">+</span> <span class="n">name</span><span class="o">.</span><span class="n">encode</span><span class="p">(</span><span class="s1">'punycode'</span><span class="p">)</span><span class="o">.</span><span class="n">replace</span><span class="p">(</span><span class="sa">b</span><span class="s1">'-'</span><span class="p">,</span> <span class="sa">b</span><span class="s1">'_'</span><span class="p">)</span> <span class="k">return</span> <span class="sa">b</span><span class="s1">'PyInit'</span> <span class="o">+</span> <span class="n">suffix</span> </pre></div> </div> <p>It is possible to export multiple modules from a single shared library by defining multiple initialization functions. However, importing them requires using symbolic links or a custom importer, because by default only the function corresponding to the filename is found. See the <em>“Multiple modules in one library”</em> section in <span class="target" id="index-1"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-0489"><strong>PEP 489</strong></a> for details.</p> <div class="section" id="building-c-and-c-extensions-with-distutils"> <h2>4.1. Building C and C++ Extensions with distutils<a class="headerlink" href="#building-c-and-c-extensions-with-distutils" title="Permalink to this headline">¶</a></h2> <p>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.</p> <p>A distutils package contains a driver script, <code class="file docutils literal notranslate"><span class="pre">setup.py</span></code>. This is a plain Python file, which, in the most simple case, could look like this:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">from</span> <span class="nn">distutils.core</span> <span class="k">import</span> <span class="n">setup</span><span class="p">,</span> <span class="n">Extension</span> <span class="n">module1</span> <span class="o">=</span> <span class="n">Extension</span><span class="p">(</span><span class="s1">'demo'</span><span class="p">,</span> <span class="n">sources</span> <span class="o">=</span> <span class="p">[</span><span class="s1">'demo.c'</span><span class="p">])</span> <span class="n">setup</span> <span class="p">(</span><span class="n">name</span> <span class="o">=</span> <span class="s1">'PackageName'</span><span class="p">,</span> <span class="n">version</span> <span class="o">=</span> <span class="s1">'1.0'</span><span class="p">,</span> <span class="n">description</span> <span class="o">=</span> <span class="s1">'This is a demo package'</span><span class="p">,</span> <span class="n">ext_modules</span> <span class="o">=</span> <span class="p">[</span><span class="n">module1</span><span class="p">])</span> </pre></div> </div> <p>With this <code class="file docutils literal notranslate"><span class="pre">setup.py</span></code>, and a file <code class="file docutils literal notranslate"><span class="pre">demo.c</span></code>, running</p> <div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n">python</span> <span class="n">setup</span><span class="p">.</span><span class="n">py</span> <span class="n">build</span> </pre></div> </div> <p>will compile <code class="file docutils literal notranslate"><span class="pre">demo.c</span></code>, and produce an extension module named <code class="docutils literal notranslate"><span class="pre">demo</span></code> in the <code class="file docutils literal notranslate"><span class="pre">build</span></code> directory. Depending on the system, the module file will end up in a subdirectory <code class="file docutils literal notranslate"><span class="pre">build/lib.system</span></code>, and may have a name like <code class="file docutils literal notranslate"><span class="pre">demo.so</span></code> or <code class="file docutils literal notranslate"><span class="pre">demo.pyd</span></code>.</p> <p>In the <code class="file docutils literal notranslate"><span class="pre">setup.py</span></code>, all execution is performed by calling the <code class="docutils literal notranslate"><span class="pre">setup</span></code> 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 <a class="reference internal" href="../distutils/index.html#distutils-index"><span class="std std-ref">Distributing Python Modules (Legacy version)</span></a> to learn more about the features of distutils; this section explains building extension modules only.</p> <p>It is common to pre-compute arguments to <code class="xref py py-func docutils literal notranslate"><span class="pre">setup()</span></code>, to better structure the driver script. In the example above, the <code class="docutils literal notranslate"><span class="pre">ext_modules</span></code> argument to <a class="reference internal" href="../distutils/apiref.html#distutils.core.setup" title="distutils.core.setup"><code class="xref py py-func docutils literal notranslate"><span class="pre">setup()</span></code></a> is a list of extension modules, each of which is an instance of the <code class="xref py py-class docutils literal notranslate"><span class="pre">Extension</span></code>. In the example, the instance defines an extension named <code class="docutils literal notranslate"><span class="pre">demo</span></code> which is build by compiling a single source file, <code class="file docutils literal notranslate"><span class="pre">demo.c</span></code>.</p> <p>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.</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">from</span> <span class="nn">distutils.core</span> <span class="k">import</span> <span class="n">setup</span><span class="p">,</span> <span class="n">Extension</span> <span class="n">module1</span> <span class="o">=</span> <span class="n">Extension</span><span class="p">(</span><span class="s1">'demo'</span><span class="p">,</span> <span class="n">define_macros</span> <span class="o">=</span> <span class="p">[(</span><span class="s1">'MAJOR_VERSION'</span><span class="p">,</span> <span class="s1">'1'</span><span class="p">),</span> <span class="p">(</span><span class="s1">'MINOR_VERSION'</span><span class="p">,</span> <span class="s1">'0'</span><span class="p">)],</span> <span class="n">include_dirs</span> <span class="o">=</span> <span class="p">[</span><span class="s1">'/usr/local/include'</span><span class="p">],</span> <span class="n">libraries</span> <span class="o">=</span> <span class="p">[</span><span class="s1">'tcl83'</span><span class="p">],</span> <span class="n">library_dirs</span> <span class="o">=</span> <span class="p">[</span><span class="s1">'/usr/local/lib'</span><span class="p">],</span> <span class="n">sources</span> <span class="o">=</span> <span class="p">[</span><span class="s1">'demo.c'</span><span class="p">])</span> <span class="n">setup</span> <span class="p">(</span><span class="n">name</span> <span class="o">=</span> <span class="s1">'PackageName'</span><span class="p">,</span> <span class="n">version</span> <span class="o">=</span> <span class="s1">'1.0'</span><span class="p">,</span> <span class="n">description</span> <span class="o">=</span> <span class="s1">'This is a demo package'</span><span class="p">,</span> <span class="n">author</span> <span class="o">=</span> <span class="s1">'Martin v. Loewis'</span><span class="p">,</span> <span class="n">author_email</span> <span class="o">=</span> <span class="s1">'martin@v.loewis.de'</span><span class="p">,</span> <span class="n">url</span> <span class="o">=</span> <span class="s1">'https://docs.python.org/extending/building'</span><span class="p">,</span> <span class="n">long_description</span> <span class="o">=</span> <span class="s1">'''</span> <span class="s1">This is really just a demo package.</span> <span class="s1">'''</span><span class="p">,</span> <span class="n">ext_modules</span> <span class="o">=</span> <span class="p">[</span><span class="n">module1</span><span class="p">])</span> </pre></div> </div> <p>In this example, <a class="reference internal" href="../distutils/apiref.html#distutils.core.setup" title="distutils.core.setup"><code class="xref py py-func docutils literal notranslate"><span class="pre">setup()</span></code></a> 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</p> <div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n">gcc</span> <span class="o">-</span><span class="n">DNDEBUG</span> <span class="o">-</span><span class="n">g</span> <span class="o">-</span><span class="n">O3</span> <span class="o">-</span><span class="n">Wall</span> <span class="o">-</span><span class="n">Wstrict</span><span class="o">-</span><span class="n">prototypes</span> <span class="o">-</span><span class="n">fPIC</span> <span class="o">-</span><span class="n">DMAJOR_VERSION</span><span class="o">=</span><span class="mi">1</span> <span class="o">-</span><span class="n">DMINOR_VERSION</span><span class="o">=</span><span class="mi">0</span> <span class="o">-</span><span class="n">I</span><span class="o">/</span><span class="n">usr</span><span class="o">/</span><span class="n">local</span><span class="o">/</span><span class="n">include</span> <span class="o">-</span><span class="n">I</span><span class="o">/</span><span class="n">usr</span><span class="o">/</span><span class="n">local</span><span class="o">/</span><span class="n">include</span><span class="o">/</span><span class="n">python2</span><span class="mf">.2</span> <span class="o">-</span><span class="n">c</span> <span class="n">demo</span><span class="p">.</span><span class="n">c</span> <span class="o">-</span><span class="n">o</span> <span class="n">build</span><span class="o">/</span><span class="n">temp</span><span class="p">.</span><span class="n">linux</span><span class="o">-</span><span class="n">i686</span><span class="o">-</span><span class="mf">2.2</span><span class="o">/</span><span class="n">demo</span><span class="p">.</span><span class="n">o</span> <span class="n">gcc</span> <span class="o">-</span><span class="n">shared</span> <span class="n">build</span><span class="o">/</span><span class="n">temp</span><span class="p">.</span><span class="n">linux</span><span class="o">-</span><span class="n">i686</span><span class="o">-</span><span class="mf">2.2</span><span class="o">/</span><span class="n">demo</span><span class="p">.</span><span class="n">o</span> <span class="o">-</span><span class="n">L</span><span class="o">/</span><span class="n">usr</span><span class="o">/</span><span class="n">local</span><span class="o">/</span><span class="n">lib</span> <span class="o">-</span><span class="n">ltcl83</span> <span class="o">-</span><span class="n">o</span> <span class="n">build</span><span class="o">/</span><span class="n">lib</span><span class="p">.</span><span class="n">linux</span><span class="o">-</span><span class="n">i686</span><span class="o">-</span><span class="mf">2.2</span><span class="o">/</span><span class="n">demo</span><span class="p">.</span><span class="n">so</span> </pre></div> </div> <p>These lines are for demonstration purposes only; distutils users should trust that distutils gets the invocations right.</p> </div> <div class="section" id="distributing-your-extension-modules"> <span id="distributing"></span><h2>4.2. Distributing your extension modules<a class="headerlink" href="#distributing-your-extension-modules" title="Permalink to this headline">¶</a></h2> <p>When an extension has been successfully build, there are three ways to use it.</p> <p>End-users will typically want to install the module, they do so by running</p> <div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n">python</span> <span class="n">setup</span><span class="p">.</span><span class="n">py</span> <span class="n">install</span> </pre></div> </div> <p>Module maintainers should produce source packages; to do so, they run</p> <div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n">python</span> <span class="n">setup</span><span class="p">.</span><span class="n">py</span> <span class="n">sdist</span> </pre></div> </div> <p>In some cases, additional files need to be included in a source distribution; this is done through a <code class="file docutils literal notranslate"><span class="pre">MANIFEST.in</span></code> file; see <a class="reference internal" href="../distutils/sourcedist.html#manifest"><span class="std std-ref">Specifying the files to distribute</span></a> for details.</p> <p>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.</p> <div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n">python</span> <span class="n">setup</span><span class="p">.</span><span class="n">py</span> <span class="n">bdist_wininst</span> <span class="n">python</span> <span class="n">setup</span><span class="p">.</span><span class="n">py</span> <span class="n">bdist_rpm</span> <span class="n">python</span> <span class="n">setup</span><span class="p">.</span><span class="n">py</span> <span class="n">bdist_dumb</span> </pre></div> </div> </div> </div> </div> </div> </div> <div class="sphinxsidebar" role="navigation" aria-label="main navigation"> <div class="sphinxsidebarwrapper"> <h3><a href="../contents.html">Table Of Contents</a></h3> <ul> <li><a class="reference internal" href="#">4. Building C and C++ Extensions</a><ul> <li><a class="reference internal" href="#building-c-and-c-extensions-with-distutils">4.1. Building C and C++ Extensions with distutils</a></li> <li><a class="reference internal" href="#distributing-your-extension-modules">4.2. Distributing your extension modules</a></li> </ul> </li> </ul> <h4>Previous topic</h4> <p class="topless"><a href="newtypes.html" title="previous chapter">3. Defining Extension Types: Assorted Topics</a></p> <h4>Next topic</h4> <p class="topless"><a href="windows.html" title="next chapter">5. Building C and C++ Extensions on Windows</a></p> <div role="note" aria-label="source link"> <h3>This Page</h3> <ul class="this-page-menu"> <li><a href="../bugs.html">Report a Bug</a></li> <li> <a href="https://github.com/python/cpython/blob/3.6/Doc/extending/building.rst" rel="nofollow">Show Source </a> </li> </ul> </div> </div> </div> <div class="clearer"></div> </div> <div class="related" role="navigation" aria-label="related navigation"> <h3>Navigation</h3> <ul> <li class="right" style="margin-right: 10px"> <a href="../genindex.html" title="General Index" >index</a></li> <li class="right" > <a href="../py-modindex.html" title="Python Module Index" >modules</a> |</li> <li class="right" > <a href="windows.html" title="5. Building C and C++ Extensions on Windows" >next</a> |</li> <li class="right" > <a href="newtypes.html" title="3. 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