def login(username,password):
    f = open("db","r",encoding="utf-8")
    for line in f:
        line = line.strip()#默認strip無參數：移除空格換行符；有參數：移除兩側指定的值
        line_list = line.split("$$")
        if user == line_list[0] and pwd == line_list[1]:
            return True
    return False
def register(username,password):
    #註冊用戶
#1打開文件2用戶名密碼
    with open("db","a",encoding="utf-8") as f:
        temp = "\n" + username + "$$" + password
        f.write(temp)
def user_exist(username):
    #一行一行查找，如果用戶名存在，returnTrue；False
    with open("db","r",encoding="utf-8") as f:
        for line in f:
            line = line.strip()
            line_list = line.split("$$")
            if line_list[0] == username:
                return True
    return False
print("歡迎來到德萊聯盟")
inp = input("1:登錄；2:註冊")
if inp == "1":
    user = input("請輸入用戶名:")
    pwd = input("請輸入密碼:")
    is_login = login(user,pwd)
    if is_login:
        print("登錄成功")
    else:
        print("登錄失敗")
elif inp == "2":
    user = input("請輸入用戶：")
    pwd = input("請輸入密碼：")
    is_exist = user_exist(user)
    if is_exist:
        print("用戶已存在，無法註冊")
    else:
        register(user,pwd)
        print("註冊成功")

跟文件結合的驗證登錄