python定时检查某个进程是否已经关闭的方法

import threading
import time
import os
import subprocess
def get_process_count(imagename):
 p = os.popen('tasklist /FI "IMAGENAME eq %s"' % imagename)
 return p.read().count(imagename)
def timer_start():
 t = threading.Timer(120,watch_func,("is running..."))
 t.start()
def watch_func(msg):
 print "I'm watch_func,",msg
 if get_process_count('main.exe') == 0 :
 print subprocess.Popen([r'D:shuajiinmain.exe'])
 timer_start()
if __name__ == "__main__":
 timer_start()
 while True:
 time.sleep(1)