username = "python"
userpassword = "123456"
while True :
    name = input("请输入用户名:")
    password = input("请输入密码:")
    if name == username and userpassword == password:
        print("登录成功!")
        print("欢迎来到贝尔编程!")
        break
    elif name!=username:
        print("用户名不存在，请重新输入：")
    else:
        print("密码错误，请重新输入：")