看到python捕获SIGINT event的文档，上面说signal这个包里的东西的功能是set handler for asynchronous event，于是背了下这两个词——asynchronous和synchronous，简称分别是async和sync，由于这两个词比较长，我们通常都用简称，而且发音也都正好不会破坏。

asynchronous： 美 [eɪ'sɪŋkrənəs]
synchronous：  美 ['sɪŋkrənəs]

以上音标来自dict.cn

Here is a minimal example program. It uses the alarm() 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 os.open() 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.

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import signal, os

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', os.O_RDWR)

signal.alarm(0)          # Disable the alarm