python判断自身是否正在运行的方法

# coding: utf-8
import os
import psutil
import time
 
def write_pid():
 pid = os.getpid()
 fp = open("pid.log",'w')
 fp.write(str(pid))
 fp.close()
 
def read_pid():
 if os.path.exists("pid.log"):
  fp = open("pid.log",'r')
  pid = fp.read()
  fp.close()
  return pid
 else:
  return False
 
def write_log(log_content):
 time_now = time.strftime("%Y-%m-%d %H:%M:%S", time.localtime())
 log_content = time_now+"---->"+log_content+os.linesep
 fp = open('recognition.log','a+')
 fp.write(log_content)
 fp.close()
 
def run():
 pid = read_pid()
 #print pid
 pid = int(pid)
 if pid:
  running_pid = psutil.pids()
  if pid in running_pid:
   log_content = "process is running..."
   write_log(log_content)
  else:
   write_pid()
   time.sleep(20)
 else:
  write_pid()
  time.sleep(20)
 
if __name__ == "__main__":
 run()