#!/usr/bin/env python
# -*- coding:utf-8 -*-
i = 0
while i< 3:
 name = raw_input("用户名：")
 pwd = raw_input("密码：")
 if name =="刘仕民"and pwd =="123":
  print("登陆成功")
  break
 elif i == 0:
  print("你还有2次输入机会")
 elif i == 1:
  print("你还有1次输入机会")
 elif i == 2:
  print("     登陆失败    ")
  print("你还有0次输入机会")
 i += 1

用户输入错误三次则退出