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<title>8.5 dl -- Call C functions in shared objects</title>
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<H1><A NAME="SECTION0010500000000000000000">
8.5 <tt class="module">dl</tt> --
         Call C functions in shared objects</A>
</H1>
<A NAME="module-dl"></A>
<p class="availability">Availability: <span
 class="platform">Unix</span>.</p>

<P>
The <tt class="module">dl</tt> module defines an interface to the
<tt class="cfunction">dlopen()</tt> function, which is the most common interface on
<span class="Unix">Unix</span> platforms for handling dynamically linked libraries. It allows
the program to call arbitrary functions in such a library.

<P>
<span class="note"><b class="label">Note:</b>
This module will not work unless
<code>sizeof(int) == sizeof(long) == sizeof(char *)</code>
If this is not the case, <tt class="exception">SystemError</tt> will be raised on
import.</span>

<P>
The <tt class="module">dl</tt> module defines the following function:

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-2988' xml:id='l2h-2988' class="function">open</tt></b>(</nobr></td>
  <td><var>name</var><big>[</big><var>, mode<code> = RTLD_LAZY</code></var><big>]</big><var></var>)</td></tr></table></dt>
<dd>
Open a shared object file, and return a handle. Mode
signifies late binding (<tt class="constant">RTLD_LAZY</tt>) or immediate binding
(<tt class="constant">RTLD_NOW</tt>). Default is <tt class="constant">RTLD_LAZY</tt>. Note that some
systems do not support <tt class="constant">RTLD_NOW</tt>.

<P>
Return value is a dlobject.
</dl>

<P>
The <tt class="module">dl</tt> module defines the following constants:

<P>
<dl><dt><b><tt id='l2h-2989' xml:id='l2h-2989'>RTLD_LAZY</tt></b></dt>
<dd>
Useful as an argument to <tt class="function">open()</tt>.
</dd></dl>

<P>
<dl><dt><b><tt id='l2h-2990' xml:id='l2h-2990'>RTLD_NOW</tt></b></dt>
<dd>
Useful as an argument to <tt class="function">open()</tt>.  Note that on systems
which do not support immediate binding, this constant will not appear
in the module. For maximum portability, use <tt class="function">hasattr()</tt> to
determine if the system supports immediate binding.
</dd></dl>

<P>
The <tt class="module">dl</tt> module defines the following exception:

<P>
<dl><dt><b><span class="typelabel">exception</span>&nbsp;<tt id='l2h-2991' xml:id='l2h-2991' class="exception">error</tt></b></dt>
<dd>
Exception raised when an error has occurred inside the dynamic loading
and linking routines.
</dd></dl>

<P>
Example:

<P>
<div class="verbatim"><pre>
&gt;&gt;&gt; import dl, time
&gt;&gt;&gt; a=dl.open('/lib/libc.so.6')
&gt;&gt;&gt; a.call('time'), time.time()
(929723914, 929723914.498)
</pre></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>

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<span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span>
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