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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="Content-Type" content="text/html; charset=utf-8" /> <title>35.6. dl — Call C functions in shared objects — Python v2.6.6 documentation</title> <link rel="stylesheet" href="../_static/default.css" type="text/css" /> <link rel="stylesheet" href="../_static/pygments.css" type="text/css" /> <script type="text/javascript"> var DOCUMENTATION_OPTIONS = { URL_ROOT: '../', VERSION: '2.6.6', COLLAPSE_MODINDEX: false, FILE_SUFFIX: '.html', HAS_SOURCE: true }; </script> <script type="text/javascript" src="../_static/jquery.js"></script> <script type="text/javascript" src="../_static/doctools.js"></script> <link rel="search" type="application/opensearchdescription+xml" title="Search within Python v2.6.6 documentation" href="../_static/opensearch.xml"/> <link rel="author" title="About these documents" href="../about.html" /> <link rel="copyright" title="Copyright" href="../copyright.html" /> <link rel="top" title="Python v2.6.6 documentation" href="../index.html" /> <link rel="up" title="35. 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Unix Specific Services</a> »</li> </ul> </div> <div class="document"> <div class="documentwrapper"> <div class="bodywrapper"> <div class="body"> <div class="section" id="module-dl"> <h1>35.6. <tt class="xref docutils literal"><span class="pre">dl</span></tt> — Call C functions in shared objects<a class="headerlink" href="#module-dl" title="Permalink to this headline">¶</a></h1> <p><em>Platforms: </em>Unix</p> <p class="deprecated"> <span class="versionmodified">Deprecated since version 2.6: </span>The <tt class="xref docutils literal"><span class="pre">dl</span></tt> module has been removed in Python 3.0. Use the <a title="A foreign function library for Python." class="reference external" href="ctypes.html#module-ctypes"><tt class="xref docutils literal"><span class="pre">ctypes</span></tt></a> module instead.</p> <p>The <tt class="xref docutils literal"><span class="pre">dl</span></tt> module defines an interface to the <tt class="xref docutils literal"><span class="pre">dlopen()</span></tt> function, which is the most common interface on Unix platforms for handling dynamically linked libraries. It allows the program to call arbitrary functions in such a library.</p> <div class="admonition warning"> <p class="first admonition-title">Warning</p> <p class="last">The <tt class="xref docutils literal"><span class="pre">dl</span></tt> module bypasses the Python type system and error handling. If used incorrectly it may cause segmentation faults, crashes or other incorrect behaviour.</p> </div> <div class="admonition note"> <p class="first admonition-title">Note</p> <p class="last">This module will not work unless <tt class="docutils literal"><span class="pre">sizeof(int)</span> <span class="pre">==</span> <span class="pre">sizeof(long)</span> <span class="pre">==</span> <span class="pre">sizeof(char</span> <span class="pre">*)</span></tt> If this is not the case, <a title="exceptions.SystemError" class="reference external" href="exceptions.html#exceptions.SystemError"><tt class="xref docutils literal"><span class="pre">SystemError</span></tt></a> will be raised on import.</p> </div> <p>The <tt class="xref docutils literal"><span class="pre">dl</span></tt> module defines the following function:</p> <dl class="function"> <dt id="dl.open"> <tt class="descclassname">dl.</tt><tt class="descname">open</tt><big>(</big><em>name</em><span class="optional">[</span>, <em>mode=RTLD_LAZY</em><span class="optional">]</span><big>)</big><a class="headerlink" href="#dl.open" title="Permalink to this definition">¶</a></dt> <dd><p>Open a shared object file, and return a handle. Mode signifies late binding (<a title="dl.RTLD_LAZY" class="reference internal" href="#dl.RTLD_LAZY"><tt class="xref docutils literal"><span class="pre">RTLD_LAZY</span></tt></a>) or immediate binding (<a title="dl.RTLD_NOW" class="reference internal" href="#dl.RTLD_NOW"><tt class="xref docutils literal"><span class="pre">RTLD_NOW</span></tt></a>). Default is <a title="dl.RTLD_LAZY" class="reference internal" href="#dl.RTLD_LAZY"><tt class="xref docutils literal"><span class="pre">RTLD_LAZY</span></tt></a>. Note that some systems do not support <a title="dl.RTLD_NOW" class="reference internal" href="#dl.RTLD_NOW"><tt class="xref docutils literal"><span class="pre">RTLD_NOW</span></tt></a>.</p> <p>Return value is a <tt class="xref docutils literal"><span class="pre">dlobject</span></tt>.</p> </dd></dl> <p>The <tt class="xref docutils literal"><span class="pre">dl</span></tt> module defines the following constants:</p> <dl class="data"> <dt id="dl.RTLD_LAZY"> <tt class="descclassname">dl.</tt><tt class="descname">RTLD_LAZY</tt><a class="headerlink" href="#dl.RTLD_LAZY" title="Permalink to this definition">¶</a></dt> <dd>Useful as an argument to <a title="dl.open" class="reference internal" href="#dl.open"><tt class="xref docutils literal"><span class="pre">open()</span></tt></a>.</dd></dl> <dl class="data"> <dt id="dl.RTLD_NOW"> <tt class="descclassname">dl.</tt><tt class="descname">RTLD_NOW</tt><a class="headerlink" href="#dl.RTLD_NOW" title="Permalink to this definition">¶</a></dt> <dd>Useful as an argument to <a title="dl.open" class="reference internal" href="#dl.open"><tt class="xref docutils literal"><span class="pre">open()</span></tt></a>. Note that on systems which do not support immediate binding, this constant will not appear in the module. For maximum portability, use <a title="hasattr" class="reference external" href="functions.html#hasattr"><tt class="xref docutils literal"><span class="pre">hasattr()</span></tt></a> to determine if the system supports immediate binding.</dd></dl> <p>The <tt class="xref docutils literal"><span class="pre">dl</span></tt> module defines the following exception:</p> <dl class="exception"> <dt id="dl.error"> <em class="property">exception </em><tt class="descclassname">dl.</tt><tt class="descname">error</tt><a class="headerlink" href="#dl.error" title="Permalink to this definition">¶</a></dt> <dd>Exception raised when an error has occurred inside the dynamic loading and linking routines.</dd></dl> <p>Example:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">dl</span><span class="o">,</span> <span class="nn">time</span> <span class="gp">>>> </span><span class="n">a</span><span class="o">=</span><span class="n">dl</span><span class="o">.</span><span class="n">open</span><span class="p">(</span><span class="s">'/lib/libc.so.6'</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">a</span><span class="o">.</span><span class="n">call</span><span class="p">(</span><span class="s">'time'</span><span class="p">),</span> <span class="n">time</span><span class="o">.</span><span class="n">time</span><span class="p">()</span> <span class="go">(929723914, 929723914.498)</span> </pre></div> </div> <p>This example was tried on a Debian GNU/Linux system, and is a good example of the fact that using this module is usually a bad alternative.</p> <div class="section" id="dl-objects"> <span id="id1"></span><h2>35.6.1. Dl Objects<a class="headerlink" href="#dl-objects" title="Permalink to this headline">¶</a></h2> <p>Dl objects, as returned by <a title="dl.open" class="reference internal" href="#dl.open"><tt class="xref docutils literal"><span class="pre">open()</span></tt></a> above, have the following methods:</p> <dl class="method"> <dt id="dl.dl.close"> <tt class="descclassname">dl.</tt><tt class="descname">close</tt><big>(</big><big>)</big><a class="headerlink" href="#dl.dl.close" title="Permalink to this definition">¶</a></dt> <dd>Free all resources, except the memory.</dd></dl> <dl class="method"> <dt id="dl.dl.sym"> <tt class="descclassname">dl.</tt><tt class="descname">sym</tt><big>(</big><em>name</em><big>)</big><a class="headerlink" href="#dl.dl.sym" title="Permalink to this definition">¶</a></dt> <dd><p>Return the pointer for the function named <em>name</em>, as a number, if it exists in the referenced shared object, otherwise <tt class="xref docutils literal"><span class="pre">None</span></tt>. This is useful in code like:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="k">if</span> <span class="n">a</span><span class="o">.</span><span class="n">sym</span><span class="p">(</span><span class="s">'time'</span><span class="p">):</span> <span class="gp">... </span> <span class="n">a</span><span class="o">.</span><span class="n">call</span><span class="p">(</span><span class="s">'time'</span><span class="p">)</span> <span class="gp">... </span><span class="k">else</span><span class="p">:</span> <span class="gp">... </span> <span class="n">time</span><span class="o">.</span><span class="n">time</span><span class="p">()</span> </pre></div> </div> <p>(Note that this function will return a non-zero number, as zero is the <em>NULL</em> pointer)</p> </dd></dl> <dl class="method"> <dt id="dl.dl.call"> <tt class="descclassname">dl.</tt><tt class="descname">call</tt><big>(</big><em>name</em><span class="optional">[</span>, <em>arg1</em><span class="optional">[</span>, <em>arg2...</em><span class="optional">]</span><span class="optional">]</span><big>)</big><a class="headerlink" href="#dl.dl.call" title="Permalink to this definition">¶</a></dt> <dd><p>Call the function named <em>name</em> in the referenced shared object. The arguments must be either Python integers, which will be passed as is, Python strings, to which a pointer will be passed, or <tt class="xref docutils literal"><span class="pre">None</span></tt>, which will be passed as <em>NULL</em>. Note that strings should only be passed to functions as <tt class="xref docutils literal"><span class="pre">const</span> <span class="pre">char*</span></tt>, as Python will not like its string mutated.</p> <p>There must be at most 10 arguments, and arguments not given will be treated as <tt class="xref docutils literal"><span class="pre">None</span></tt>. The function’s return value must be a C <tt class="xref docutils literal"><span class="pre">long</span></tt>, which is a Python integer.</p> </dd></dl> </div> </div> </div> </div> </div> <div class="sphinxsidebar"> <div class="sphinxsidebarwrapper"> <h3><a href="../contents.html">Table Of Contents</a></h3> <ul> <li><a class="reference external" href="#">35.6. <tt class="docutils literal"><span class="pre">dl</span></tt> — Call C functions in shared objects</a><ul> <li><a class="reference external" href="#dl-objects">35.6.1. Dl Objects</a></li> </ul> </li> </ul> <h4>Previous topic</h4> <p class="topless"><a href="crypt.html" title="previous chapter">35.5. <tt class="docutils literal docutils literal"><span class="pre">crypt</span></tt> — Function to check Unix passwords</a></p> <h4>Next topic</h4> <p class="topless"><a href="termios.html" title="next chapter">35.7. <tt class="docutils literal"><span class="pre">termios</span></tt> — POSIX style tty control</a></p> <h3>This Page</h3> <ul class="this-page-menu"> <li><a href="../bugs.html">Report a Bug</a></li> <li><a href="../_sources/library/dl.txt" rel="nofollow">Show Source</a></li> </ul> <div id="searchbox" style="display: none"> <h3>Quick search</h3> <form class="search" action="../search.html" method="get"> <input type="text" name="q" size="18" /> <input type="submit" value="Go" /> <input type="hidden" name="check_keywords" value="yes" /> <input type="hidden" name="area" value="default" /> </form> <p class="searchtip" style="font-size: 90%"> Enter search terms or a module, class or function name. </p> </div> <script type="text/javascript">$('#searchbox').show(0);</script> </div> </div> <div class="clearer"></div> </div> <div class="related"> <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="../modindex.html" title="Global Module Index" >modules</a> |</li> <li class="right" > <a href="termios.html" title="35.7. termios — POSIX style tty control" >next</a> |</li> <li class="right" > <a href="crypt.html" title="35.5. crypt — Function to check Unix passwords" >previous</a> |</li> <li><img src="../_static/py.png" alt="" style="vertical-align: middle; margin-top: -1px"/></li> <li><a href="../index.html">Python v2.6.6 documentation</a> »</li> <li><a href="index.html" >The Python Standard Library</a> »</li> <li><a href="unix.html" >35. 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