diy.py

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 password == userpassword:
        print("登陆成功")
        break
    if name != username:
        print("用户名不存在，请重新输入！")
        continue
    if password != userpassword:
        print("密码错误，请重新输入！")
print("欢迎来到贝尔编程！")