How to use the write/read log file

Question

I am new to python and I am trying to write a program, when every time a user inputs a incorrect/failed password attempt it will write it into a file. Which records the time/date and the reason why its invalid. Then should display the output.

I've tried running my code but it always comes up with an error:

log_file.write({todays_date},{reason_password_invalid}) UnboundLocalError: local variable 'todays_date' referenced before assignment

I am not sure why that it. Is my code not correctly written to be able write into a file every time it is incorrect?

import datetime

def main():
MIN_PASSWORD_LENGTH = 6
MAX_PASSWORD_LENGTH = 14
PASSWORD_LOG_FILE = "password_log.txt"
password = input("Enter your password: ")
password_length = len(password)

if password_length > MIN_PASSWORD_LENGTH and password_length < MAX_PASSWORD_LENGTH:

    if password.isalpha():
        message = "Your password is weak! It only contains letters."
    elif password.isnumeric():
        message = "Your password is weak! It only contains numbers."
    else:
        message = "Your password is strong! It contains letters and numbers."
else:
    my_date = datetime.datetime.today()
    todays_date = my_date.strftime("%A%B%d%Y")

    if password_length < MIN_PASSWORD_LENGTH:
        reason_password_invalid = "password_length < 6"
    else:
        reason_password_invalid = "password_length > 14"

log_file = open(PASSWORD_LOG_FILE, "a")
log_file.write({todays_date},{reason_password_invalid})
log_file.close()

log_file = open(PASSWORD_LOG_FILE, "r")
for line in log:
    print(line, end="")
log_file.close()
main()

Answer 1

The todays_date and reason_password_invalid variables are only defined in the else block of your main if statement, so you would get the said exception if the user enters a valid password.

You should write to the log file only if the user enters an invalid password instead:

else:
    my_date = datetime.datetime.today()
    todays_date = my_date.strftime("%A%B%d%Y")

    if password_length < MIN_PASSWORD_LENGTH:
        reason_password_invalid = "password_length < 6"
    else:
        reason_password_invalid = "password_length > 14"

    log_file = open(PASSWORD_LOG_FILE, "a")
    log_file.write(f'{todays_date},{reason_password_invalid}\n')
    log_file.close()