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<div class="section" id="module-dl">
<span id="dl-call-c-functions-in-shared-objects"></span><h1>36.6. <a class="reference internal" href="#module-dl" title="dl: Call C functions in shared objects. (deprecated) (Unix)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">dl</span></code></a> — Call C functions in shared objects<a class="headerlink" href="#module-dl" title="Permalink to this headline">¶</a></h1>
<div class="deprecated">
<p><span class="versionmodified">Deprecated since version 2.6: </span>The <a class="reference internal" href="#module-dl" title="dl: Call C functions in shared objects. (deprecated) (Unix)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">dl</span></code></a> module has been removed in Python 3. Use the <a class="reference internal" href="ctypes.html#module-ctypes" title="ctypes: A foreign function library for Python."><code class="xref py py-mod docutils literal notranslate"><span class="pre">ctypes</span></code></a>
module instead.</p>
</div>
<p>The <a class="reference internal" href="#module-dl" title="dl: Call C functions in shared objects. (deprecated) (Unix)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">dl</span></code></a> module defines an interface to the <code class="xref c c-func docutils literal notranslate"><span class="pre">dlopen()</span></code> 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 <a class="reference internal" href="#module-dl" title="dl: Call C functions in shared objects. (deprecated) (Unix)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">dl</span></code></a> 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 <code class="docutils literal notranslate"><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></code> If this is not the case, <a class="reference internal" href="exceptions.html#exceptions.SystemError" title="exceptions.SystemError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">SystemError</span></code></a> will be raised on import.</p>
</div>
<p>The <a class="reference internal" href="#module-dl" title="dl: Call C functions in shared objects. (deprecated) (Unix)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">dl</span></code></a> module defines the following function:</p>
<dl class="function">
<dt id="dl.open">
<code class="descclassname">dl.</code><code class="descname">open</code><span class="sig-paren">(</span><em>name</em><span class="optional">[</span>, <em>mode=RTLD_LAZY</em><span class="optional">]</span><span class="sig-paren">)</span><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 class="reference internal" href="#dl.RTLD_LAZY" title="dl.RTLD_LAZY"><code class="xref py py-const docutils literal notranslate"><span class="pre">RTLD_LAZY</span></code></a>) or immediate binding (<a class="reference internal" href="#dl.RTLD_NOW" title="dl.RTLD_NOW"><code class="xref py py-const docutils literal notranslate"><span class="pre">RTLD_NOW</span></code></a>). Default is
<a class="reference internal" href="#dl.RTLD_LAZY" title="dl.RTLD_LAZY"><code class="xref py py-const docutils literal notranslate"><span class="pre">RTLD_LAZY</span></code></a>. Note that some systems do not support <a class="reference internal" href="#dl.RTLD_NOW" title="dl.RTLD_NOW"><code class="xref py py-const docutils literal notranslate"><span class="pre">RTLD_NOW</span></code></a>.</p>
<p>Return value is a <code class="xref py py-class docutils literal notranslate"><span class="pre">dlobject</span></code>.</p>
</dd></dl>
<p>The <a class="reference internal" href="#module-dl" title="dl: Call C functions in shared objects. (deprecated) (Unix)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">dl</span></code></a> module defines the following constants:</p>
<dl class="data">
<dt id="dl.RTLD_LAZY">
<code class="descclassname">dl.</code><code class="descname">RTLD_LAZY</code><a class="headerlink" href="#dl.RTLD_LAZY" title="Permalink to this definition">¶</a></dt>
<dd><p>Useful as an argument to <a class="reference internal" href="#dl.open" title="dl.open"><code class="xref py py-func docutils literal notranslate"><span class="pre">open()</span></code></a>.</p>
</dd></dl>
<dl class="data">
<dt id="dl.RTLD_NOW">
<code class="descclassname">dl.</code><code class="descname">RTLD_NOW</code><a class="headerlink" href="#dl.RTLD_NOW" title="Permalink to this definition">¶</a></dt>
<dd><p>Useful as an argument to <a class="reference internal" href="#dl.open" title="dl.open"><code class="xref py py-func docutils literal notranslate"><span class="pre">open()</span></code></a>. Note that on systems which do not
support immediate binding, this constant will not appear in the module. For
maximum portability, use <a class="reference internal" href="functions.html#hasattr" title="hasattr"><code class="xref py py-func docutils literal notranslate"><span class="pre">hasattr()</span></code></a> to determine if the system supports
immediate binding.</p>
</dd></dl>
<p>The <a class="reference internal" href="#module-dl" title="dl: Call C functions in shared objects. (deprecated) (Unix)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">dl</span></code></a> module defines the following exception:</p>
<dl class="exception">
<dt id="dl.error">
<em class="property">exception </em><code class="descclassname">dl.</code><code class="descname">error</code><a class="headerlink" href="#dl.error" title="Permalink to this definition">¶</a></dt>
<dd><p>Exception raised when an error has occurred inside the dynamic loading and
linking routines.</p>
</dd></dl>
<p>Example:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><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="s1">'/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="s1">'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>36.6.1. Dl Objects<a class="headerlink" href="#dl-objects" title="Permalink to this headline">¶</a></h2>
<p>Dl objects, as returned by <a class="reference internal" href="#dl.open" title="dl.open"><code class="xref py py-func docutils literal notranslate"><span class="pre">open()</span></code></a> above, have the following methods:</p>
<dl class="method">
<dt id="dl.dl.close">
<code class="descclassname">dl.</code><code class="descname">close</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#dl.dl.close" title="Permalink to this definition">¶</a></dt>
<dd><p>Free all resources, except the memory.</p>
</dd></dl>
<dl class="method">
<dt id="dl.dl.sym">
<code class="descclassname">dl.</code><code class="descname">sym</code><span class="sig-paren">(</span><em>name</em><span class="sig-paren">)</span><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 <code class="docutils literal notranslate"><span class="pre">None</span></code>. This is useful in code like:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><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="s1">'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="s1">'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">
<code class="descclassname">dl.</code><code class="descname">call</code><span class="sig-paren">(</span><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><span class="sig-paren">)</span><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 <code class="docutils literal notranslate"><span class="pre">None</span></code>, which will be passed as <em>NULL</em>.
Note that strings should only be passed to functions as <code class="xref c c-type docutils literal notranslate"><span class="pre">const</span> <span class="pre">char*</span></code>,
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
<code class="docutils literal notranslate"><span class="pre">None</span></code>. The function’s return value must be a C <code class="xref c c-type docutils literal notranslate"><span class="pre">long</span></code>, which is a
Python integer.</p>
</dd></dl>
</div>
</div>
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<h3><a href="../contents.html">Table Of Contents</a></h3>
<ul>
<li><a class="reference internal" href="#">36.6. <code class="docutils literal notranslate"><span class="pre">dl</span></code> — Call C functions in shared objects</a><ul>
<li><a class="reference internal" href="#dl-objects">36.6.1. Dl Objects</a></li>
</ul>
</li>
</ul>
<h4>Previous topic</h4>
<p class="topless"><a href="crypt.html"
title="previous chapter">36.5. <code class="docutils literal notranslate"><span class="pre">crypt</span></code> — Function to check Unix passwords</a></p>
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