Global variable cannot be modify in function-CodePudding

login_success = False


def user_login():
    login_username = input("Enter your username to login.\n")
    login_password = input("Enter your password to login.\n")

    credentials_checking = open("user_credentials.txt", "r")
    while not login_success:
        for line in credentials_checking:
            credential_element = line.split(" | ")
            if login_username == credential_element[0] and login_password == credential_element[1][:-1]:
                print("Login successful!")
            else:
                login_success = True
                break
    credentials_checking.close()

login_success is a global variable but unfortunately an error occur. (This project do not allow the use of global function)The output are as below:

Output:

UnboundLocalError: local variable 'login_success' referenced before assignment

CodePudding user response：

Python functions treat all variables as they haven't been created yet, you just need to add global login_success to the function.

def user_login():
    global login_success
    # all other code

CodePudding user response：

You need to use the keyword global. Right now, Python thinks you're trying to refer to a local variable named login_success. To fix this, add the following line to your function:

def user_login():
    global login_success
    ...