python定时检查某个进程是否已经关闭的方法

import threadingimport timeimport osimport subprocessdef 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:/shuaji/bin/main.exe'])  timer_start()if __name__ == "__main__":  timer_start()  while True:    time.sleep(1)