signal handler that me understand

signal_handler_me_understand.py

# 1，2，3，4，5，-1，0，1，2...
import signal
import sys

count = 0  

def signal_handler(signum, frame):
    global count
    count = -1
    print 'sig', count

def main():
    signal.signal(signal.SIGALRM, signal_handler)
    signal.setitimer(signal.ITIMER_REAL, 1, 1)
    global count
    while True:
        for line in sys.stdin:
            x = count
            count += 1
            print count

if __name__ == "__main__":
    main()