import os
import sys
import getpass
login_username = 'admin'
login_password = '12345'
u = 0
while u < 3:
    username = input('请输入用户名:')
    is_change_pwd = 0;
    if username == login_username:
        p = 0
        while p < 3 :
            if is_change_pwd == 0:
                password = input('请输入密码：')
                if password == login_password:
                    print('欢迎%s登录管理平台,' % username)
                    sys.exit(0)
                else:
                    if p != 2:
                        print('用户%s密码错误,请重新输入，还有%d次机会' % (username, 2 - p))
                p += 1
                if p == 3:
                    password_modify = input('是否要修改密码：')
                    if password_modify != 'n':
                        p = 0
                        is_change_pwd = 1
            else:
                new_password = input('请输入新的密码：')
                login_password = new_password
                print('密码修改成功')
                is_change_pwd = 0
        else:
            print('用户 %s 达到最大登录次数，将被锁定并退出' % username)
            break
    else:
        if u != 2:
            print('用户%s 不存在，请重新输入，还有%d 次机会' %(username,2 - u))
    u += 1
else:
   sys.exit('因为您的错误输入，程序已经退出，请重新运行')