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<H2><A NAME="SECTION009110000000000000000">
7.1.1 Example</A>
</H2>

<P>
Here is a minimal example program. It uses the <tt class=function>alarm()</tt>
function to limit the time spent waiting to open a file; this is
useful if the file is for a serial device that may not be turned on,
which would normally cause the <tt class=function>os.open()</tt> to hang
indefinitely.  The solution is to set a 5-second alarm before opening
the file; if the operation takes too long, the alarm signal will be
sent, and the handler raises an exception.

<P>
<dl><dd><pre class=verbatim>
import signal, os, FCNTL

def handler(signum, frame):
    print 'Signal handler called with signal', signum
    raise IOError, "Couldn't open device!"

# Set the signal handler and a 5-second alarm
signal.signal(signal.SIGALRM, handler)
signal.alarm(5)

# This open() may hang indefinitely
fd = os.open('/dev/ttyS0', FCNTL.O_RDWR)  

signal.alarm(0)          # Disable the alarm
</pre></dl><p>
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