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:\shuaji\bin\main.exe'])
  timer_start()
if __name__ == "__main__":
  timer_start()
  while True:
    time.sleep(1)