python保证只运行一个实例

最近有需求希望进程启动的时候能kill掉已经运行的实例

#!/usr/bin/env python
# encoding: utf-8
import time
import os
import sys
import subprocess
def killOldProcess():
    # kill 已有的进程id
    with open('pid.txt', 'a+') as f:
        old_pid = f.readline()
        if old_pid :
            # 确定进程id是运行的当前程序，防止误杀
            ps_info = os.popen("ps -ef | grep %s | awk '{print $2}'" % __file__)
            if old_pid in ps_info:
                os.system('kill -9 %s' % old_pid)
    # 保存当前进程id
    with open('pid.txt', 'w') as f :
        f.write('%d\n' % os.getpid())
if __name__ == '__main__':
    killOldProcess()
    while True :
        time.sleep(1)