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<title>7.1.1 Example
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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.
<div class=
"verbatim"><pre>
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)
# This open() may hang indefinitely
fd = os.open('/dev/ttyS0', os.O_RDWR)
signal.alarm(
0) # Disable the alarm
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<span class=
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2.4.2, documentation updated on
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2005.
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