如何在 python 中搜索 SQL 列表以检查用户名是否与用户输入匹配？

Question

So I am making a login page, and I need to compare the username of an SQL list to the user input. I will also use the answer for the password. This is what I have tried and it returns false.

list_of_users = [('joe@gmail.com', 'qwerty'), ('jeremy', '123')]

for i in list_of_users:
    if i == 'joe@gmail.com':
        print("True")
    else:
        print("False")

The list_of_users is there to simulate what the SQL gives when you do cursor.fetchall() on an SQL database. Any input would be appriciated!

Answer 1

Because the elements of your list are tuples of two elements. So each element has two in turn. See the definition in the official documentation of Data Structures - Tuples and Sequences .

If you wanted to fix your code, you would then simply add a second element to the for loop:

list_of_users = [('joe@gmail.com', 'qwerty'), ('jeremy', '123')]

for email, pwd in list_of_users:
    if email == 'joe@gmail.com':
        print("True")
    else:
        print("False")

But this approach has a fundamental flaw for your use case . You want to print N times 'false'? Just iterate until the mail is found and stop.

This is an example toy code:

list_of_users = [('joe@gmail.com', 'qwerty'), ('jeremy', '123')]


def login(email: str, pwd: str, list_of_users: [()]) -> bool:
    for db_email, db_pwd in list_of_users:
         if (email == db_email) and (pwd == db_pwd):
             return True
    return False


print(login('jeremy', '123', list_of_users))  # True
print(login('jeremy', '456', list_of_users))  # False