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<FONT><h3>Optional Operational System</h3>
<p>The next set of modules implements interfaces to optional operational system features. Keep in mind that these features are not available for all platforms.</p>
<H4><TT Class="monofont">signal</TT></H4>
<P>The <tt clASS="monofont">signal</Tt> module provides mechanisms to access <tt class="monofont">POSIX</tt> signals in order to let the programmer set her own signal handlers for asynchronous events.</p>
<p>A good example is the case when it is necessary to monitor the users, checking whether they press CTRL+C to stop the execution of a program. Although Python provides default handlers, you can overwrite them by creating your own.</p>
<pre>
import signal, sys
def signal_handler(signal, frame):
print "You have pressed CTRL+C"
signal.signal(signal.SIGINT, signal.SIG_IGN)
print "Now, you can\ 't stop the script with CTRL+C " }
"for the next 10 seconds!"
signal.signal(signal.SIGALRM, alarm_handler)
signal.alarm(10)
while 1:
print "I am looping"
def alarm_handler(signal, frame):
print "Now you can leave the program"
sys.exit(0)
signal.signal(signal.SIGINT, signal_handler)
print "Press CTRL+C"
while 1:
continue
</pre>
<p>Some of the available signals you can use are as follows:</P>
<p><tAble BordeR="1" celLSPAcing="0" CELLpaddING="1" Width="100%">
<COLGroup align="left" span="2">
<tr valigN="top">
<td>
<Font Size="2">SIGALRM</fOnt></tD>
<TD>
<Font sIZE="2">Alarm</Font></tD>
</TR>
<Tr valIGN="top">
<Td>
<font size="2">SIGCONT</font></td>
<td>
<fonT siZe="2">Continue</foNt></td>
</tR>
<tr vALIGn="top">
<td>
<fONT Size="2">SIGING</fONT></Td>
<td>
<fONT Size="2">Terminal interrupt character</font></td>
</tr>
<tr valign="top">
<tD>
<foNt siZe="2">SIGQUIT</fonT></td>
<tD>
<FONt sizE="2">Terminal Quit character</FONt></td>
</tR>
<TR ValigN="top">
<TD>
<Font size="2">SIGTERM</font></td>
<td>
<font sIze="2">Termination</Font></Td>
</tr>
<tR valIGN="top">
<Td>
<fonT SIZe="2">SIG_IGN</fonT></TD>
<Td>
<fonT SIZe="2">Signal handler that ignores a signal<a name="idx1073742931"></a><a name="idx1073742932"></a>
</font></td>
</tR>
</coLgroUp>
</tabLe></p>
<h4><TT CLass="monofont">socket</tT></H4>
<P>The <Tt claSS="monofont">socket</TT> module provides access to a low-level BSD socket-style network interface.</p>
<p>See <a hREF="161.html">Chapter 10, "Basic Network Background,"</A> for details.</p>
<h4><tt class="monofont">select</tt></h4>
<p>The <tt class="monofont">select</Tt> module is used to implement polling and to multiplex processing across multiple I/O streams without using threads or subprocesses. It provides access to the BSD <tT claSs="monofont">select()</tt> function interface, available in most operating systems.<a Name="idx1073742933"></A><A NAme="idx1073742934"></a></p>
<P>On windows it only works for <TT Class="monofont">sockets.</TT> On UNIX, it is used for <TT clasS="monofont">pipes,</TT>
<Tt class="monofont">sockets,</tt>
<tt class="monofont">files,</tt> and so on.</p>
<p>See <a HreF="161.html">Chapter 10</a> for details.</p>
<h4><Tt claSs="monofont">thread</tt></H4>
<P>The <TT clasS="monofont">thread</TT> module supports lightweight process threads. It offers a low-level interface for working with multiple threads.</P>
<p>See <a hrEF="148.html">Chapter 9</A> for details.</P>
<h4><tt cLASS="monofont">threading</tt></h4>
<p>The <tt class="monofont">threading</tt> module provides high-level threading interfaces on top of the <tt class="monofont">thread</Tt> module.</p>
<P>See <a hrEf="148.html">Chapter 9</a> for details.</p>
<h4><Tt clASS="monofont">Queue</Tt></h4>
<p>The <tT CLAss="monofont">Queue</tt> module is a synchronized <I>queue class</I> that is used in thread programming to move Python objects between multiple threads.</P>
<P>See <a hreF="148.html">Chapter 9</A> for details. <A Name="idx1073742935"></a><a name="idx1073742936"></a></p>
<h4><tt class="monofont">anydbm</tT></h4>
<p>The <Tt clAss="monofont">anydbm</tt> module is a generic <Tt clASS="monofont">dbm-style</Tt> interface to access variants of the <tt cLASS="monofont">dbm</tt> database.</p>
<p>See <A HREf="139.html">Chapter 8</a> for details.</p>
<h4><TT CLass="monofont">dumbdbm</tt></h4>
<p>The <tt class="monofont">dumbdbm</tt> module is a simple, portable, and slow database implemented entirely in Python.</p>
<p>See <a hRef="139.html">Chapter 8</A> for details.</p>
<h4><tT clasS="monofont">dbhash</tt></h4>
<P>The <TT Class="monofont">dbhash</TT> module provides a function that offers a <TT clasS="monofont">dbm-style</TT> interface to access the BSD database library.</P>
<p>See <a hrEF="139.html">Chapter 8</A> for details.<A name="idx1073742937"></a><a name="idx1073742938"></a></p>
<h4><tt class="monofont">whichdb</Tt></h4>
<P>The <tt cLass="monofont">whichdb</tT> module provides a function that guesses which <tt cLASS="monofont">dbm module</tt> (<tt CLASs="monofont">dbm,</tt>
<tT CLAss="monofont">gdbm,</tt> or <TT CLass="monofont">dbhash</tt>) should be used to open a specific database.</p>
<p>See <a href="139.html">Chapter 8</a> for details.</p>
<h4><tt claSs="monofont">bsddb</tT></h4>
<p>The <tT clasS="monofont">bsddb</tt> module provides an interface to access routines from the Berkeley <tT CLAss="monofont">db</tt> library.</P>
<P>See <A Href="139.html">Chapter 8</a> for details.</P>
<H4><TT clasS="monofont">zlib</TT></H4>
<p>The <tt class="monofont">zlib</tt> module provides functions that allow compression and decompression using the <tt class="monofont">zlib</tt> library. The compression that is provided by this module is compatible with <tT clAss="monofont">gzip.</tT></p>
<p>For more details check out the <tt ClasS="monofont">zlib</TT> library home page at <A targET="_blank" HRef="http://www.cdrom.com/pub/infozip/lib">http://www.cdrom.com/pub/infozip/lib</a>.</p>
<H4><TT Class="monofont">gzip</TT></H4>
<P>The <tt class="monofont">gzip</tt> module offers support for <tt class="monofont">gzip</tt> files. This module provides functions that allow compression and decompression using the GNU compression program <tt ClaSs="monofont">gzip.</tt></P>
<p>This module has a class named <tt cLass="monofont">GzipFile</TT> that can be used to read and write files compatible with the GNU <TT clasS="monofont">gzip</TT> program. The objects that are generated by this class behave just like file objects. The only exception is that the <Tt claSS="monofont">seek</TT> and <tt clASS="monofont">tell</Tt> methods aren't part of the standard implementation.</p>
<pre>
>>> import gzip
>>> gzipfile = gzip.GzipFile("backup.gz")
>>> contents = gzipfile.read()
>>> print contents
</pre>
<h4><tt class="monofont"><a namE="idx1073742939"></a><a Name="idx1073742940"></A>rlcompleter</tt></h4>
<p>The <Tt clASS="monofont">rlcompleter</Tt> module provides a <a naME="idx1073742941"></A><A name="idx1073742942"></A><I>completion function</I> for the <Tt claSS="monofont">readline</TT> module.</p>
<p>The <tt class="monofont">readline</tt> module is a UNIX module that is automatically imported by <tt class="monofont">rlcompleter.</tt> It uses a compatible GNU readline library to activate input editing on UNIX.<A naMe="idx1073742943"></a><a Name="idx1073742944"></a></P>
</fonT>
<P><TABLE width="100%" border=0><TR valign="top"><TD><font size=1 color="#C0C0C0"><br></font></TD><TD align=right><font size=1 color="#C0C0C0">Last updated on 1/30/2002<br>Python Developer's Handbook, © 2002 Sams Publishing</font></TD></TR></TABLE></P>
<TABLE border=0 width="100%" cellspacing=0 cellpadding=0><TR><td align=left width="15%" class="headingsubbarbg"><a href="75.html" title="Generic Operational System"><font size="1">< BACK</font></a></td><td align=center width="70%" class="headingsubbarbg"><font size="1"><a href="popanote.asp?pubui=oreilly&bookname=0672319942&snode=76" target="_blank" title="Make a public or private annnotation">Make Note</a> | <a href="76.html" title="Use a Safari bookmark to remember this section">Bookmark</a></font></td><td align=right width="15%" class="headingsubbarbg"><a href="77.html" title="Debugger"><font size="1">CONTINUE ></font></a></td></TR></TABLE>
</TD></TR></TABLE>
<br><TABLE width=100% bgcolor=white border=0 cellspacing=0 cellpadding=5><TR><TD><H4 class=Title>Index terms contained in this section</H4>
<font size=2>
<a href="#idx1073742941">completion function</a><BR>
functions<BR>
<a href="#idx1073742942">completion</a><BR>
libraries<BR>
<a href="#idx1073742933">Optional Operational System</a> <a href="#idx1073742937">2nd</a> <a href="#idx1073742943">3rd</a><BR>
modules<BR>
<a href="#idx1073742940">rlcompleter</a><BR>
<a href="#idx1073742932">signal</a> <a href="#idx1073742936">2nd</a><BR>
<a href="#idx1073742934">Optional Operational System library</a> <a href="#idx1073742938">2nd</a> <a href="#idx1073742944">3rd</a><BR>
<a href="#idx1073742939">rlcompleter module</a><BR>
<a href="#idx1073742931">signal module</a> <a href="#idx1073742935">2nd</a><BR>
<BR>
</font></TD></TR></TABLE>
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