diy2.py

username = "python"
userpassword = "123456"
i=0
while True:
    if i<3:
        name = input("请输入用户名:")
        password = input("请输入密码:")
        i=i+1
        if name == username and password == userpassword:
            print("登录成功!")
            break
        if name!=username:
            print("用户名不存在，请重新输入！")
        if password!=userpassword:
            print("密码不正确，请重行输入！")
    else:
        print("限定次数已用完！")
        exit()
print("欢迎来到贝尔编程!")