diy2.py

i=3
username="python"
userpassword="123456"
while True:
    if i>0:
        name = input("请输入用户名:")
        password = input("请输入密码:")
        i-=1
        if name == username and password == userpassword:
            print("登录成功!")
            break
        if name != username:
            print("用户名不存在")
            continue
        if password != userpassword:
            print("密码错误")
    else:
        print("无次数，改天在输入")
        exit()
print("欢迎来到贝尔编程!")