CS50 2022 psets6 credit problem solution

credit.py

# TODO
import sys


def main():

    # Get card number from the user

    credit_card_number = get_credit_card_number()

    # validate the card provided by the user 

    validate_card(credit_card_number)

# execute until user input a valid credit card number


def get_credit_card_number():

    # prompt user for card number

    while True:
        card_number = input("Number: ")

        # calculate card length

        try:
            if len(card_number) > 0 and int(card_number):
                break
        except ValueError:
            continue
    return card_number

# validate the user input creadit card number


def validate_card(credit_card_number):
    if len(credit_card_number) < 13 or 16 < len(credit_card_number):
        print("INVALID")
        sys.exit(0)

    even_number, odd_number = 0, 0
    card_number_length = len(credit_card_number)

    # Calculates sum according to Luhn's Algorithm

    if card_number_length % 2 == 0:
        for numbers in range(card_number_length):
            number = int(credit_card_number[numbers])
            if numbers % 2 == 0:
                multiple = number * 2
                if multiple >= 10:
                    even_number += multiple // 10
                    even_number += multiple % 10
                else:
                    even_number += multiple
            else:
                odd_number += number
    else:
        for numbers in range(card_number_length):
            number = int(credit_card_number[numbers])
            if numbers % 2 != 0:
                multiple = number * 2
                if multiple >= 10:
                    even_number += multiple // 10
                    even_number += multiple % 10
                else:
                    even_number += multiple
            else:
                odd_number += number

    checksum = (even_number + odd_number) % 10

    # Check for conditions of all companies

    if checksum == 0:
        first_digit = int(credit_card_number[0])
        second_digit = int(credit_card_number[1])
        if first_digit == 3 and second_digit == 4 or second_digit == 7:
            print("AMEX")
        elif first_digit == 5 and 1 <= second_digit <= 5:
            print("MASTERCARD")
        elif first_digit == 4:
            print("VISA")
        else:
            print("INVALID")


if __name__ == "__main__":
    main()