python - 与用户输入相比，用户登录从文件读取失败

Question

我正在编写一个程序来验证用户名:

def user_login():
    """ Login and create a username, maybe """
    with open('username.txt', 'r') as f:
        if f.readline() is "":
            username = raw_input("First login, enter a username to use: ")
            with open('username.txt', 'a+') as user:
                user.write(username)
        else:
            login_id = raw_input("Enter username: ")
            if login_id == str(f.readline()):
                return True
            else:
                print "Invalid username."
                return False


if __name__ == '__main__':
    if user_login() is not True:
        print "Failed to verify"

每次我运行它时，它都会输出以下内容:

Enter username: tperkins91
Invalid username.
Failed to verify

如何比较用户输入和从文件中读取的内容？

Answer 1

在另一个嵌套上下文中再次打开同一文件不是一个好主意。相反，在追加模式下打开一次文件，并在需要时使用f.seek(0)返回到开头:

def user_login():
    """ Login and create a username, maybe """
    with open('username.txt', 'a+') as f:
        if f.readline() is "":
            username = raw_input("First login, enter a username to use: ")
            f.seek(0)
            f.write(username)
            # return True/False --> make the function return a bool in this branch
        else:
            login_id = raw_input("Enter username: ")
            f.seek(0)
            if login_id == f.readline():
                return True
            else:
                print "Invalid username."
                return False


if __name__ == '__main__':
    if user_login() is not True:
        print "Failed to verify" 

您可能需要考虑在 if 分支中返回 bool 值，以便函数的返回类型与 bool 一致，而不是像中那样的 None目前的情况。