写一个函数完成三次登陆功能，再写一个函数完成注册功能

def register():
    while 1:
        username = input('输入用户名:')
        passwd = input('输入密码:')
        with open('homework/a.txt', 'r+', encoding='utf-8') as f:
            for item in f:
                if username == item.split("\t")[0]:
                    print("用户名存在,请重新输入")
                    break
            else:
                f.write(username + "\t" + passwd + "\n")
                return
def login():
    index = 3
    while index > 0:
        name = input("请输入用户名:")
        passwd = input("输入密码:")
        with open('homework/a.txt', 'r', encoding='utf-8') as f:
            for item in f:
                if name == item.split("\t")[0] and passwd == item.split('\t')[-1].strip():
                    print("恭喜您登陆成功")
                    return
            else:
                print("用户名密码错误,请重新登录")
                index -= 1

if __name__ == "__main__":
    register()
    login()