用户登录系统

程序示例：

users = {"user1": "123456", "user2": "123456", "user3": "123456"}
blacklist = ["user4", "user5", "user6"]
count = 1
while True:name = input("Enter your name (q to quit): ")if name == 'q':breakelse:# 用户名存在且不在黑名单内if name in users.keys():for i in range(3):password = input("Enter your password:")count += 1  # 每输入一次密码，计数器加 1if password == users[name]:print("Welcome " + name + "!")breakelse:if count < 4:print("Sorry " + name + "'s password is incorrect. Enter a different password: ")# 输出三次密码都不对，count 初始值为 1，此时为 4if count == 4:print("Sorry " + name + "'s password is incorrect. You have no chance anymore!")# 在黑名单里elif name in blacklist:print("Sorry " + name + ", you are in blacklist!")# 用户名不存在，可以注册else:print("Sorry " + name + ", you are not registered! You can register now!")password = input("Enter your password:")print("Welcome " + name + "! You are now logged on!")users[name] = password