Learn How to Work with Numbers and Strings by Implementing the Luhn Algorithm - Step 34

Python
1

Tell us what’s happening:

I’m very confused as if I try to change the card_number variable to print(‘INVALID!’) it returns with a nonetypr error on line 29 and i’m confused on what i need to do.

Your code so far

def verify_card_number(card_number):
    sum_of_odd_digits = 0
    card_number_reversed = card_number[::-1]
    odd_digits = card_number_reversed[::2]

    for digit in odd_digits:
        sum_of_odd_digits += int(digit)

    sum_of_even_digits = 0
    even_digits = card_number_reversed[1::2]
    for digit in even_digits:
        number = int(digit) * 2
        if number >= 10:
            number = (number // 10) + (number % 10)
        sum_of_even_digits += number
    total = sum_of_odd_digits + sum_of_even_digits
    print(total)
    return total % 10 == 0

# User Editable Region

def main():
    card_number = '4111-1111-4555-1142'
    card_translation = str.maketrans({'-': '', ' ': ''})
    translated_card_number = card_number.translate(card_translation)

# User Editable Region


    if verify_card_number(translated_card_number):
        print('VALID!')
    else:
        print('INVALID!')

main()

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Challenge Information:

Learn How to Work with Numbers and Strings by Implementing the Luhn Algorithm - Step 34

2

Welcome to the forum :wave:

Can you provide the exact error. An error will often have all of the information that you need to correct it.

3

what are you changing the card number to?

4

You don’t seem to have changed the value of the card_number variable? What did you try?

Do you get any hint messages?

5

Screenshot 2025-03-11 203300
Screenshot 2025-03-11 203300987×269 16.4 KB

6

what is your code when you have that error?

7

Screenshot 2025-03-11 203919
Screenshot 2025-03-11 2039191365×400 30.9 KB

8

yes it tells me to have card_number = '4111-1111-4555-1141' within the main function.

10

Is print('INVALID!') a legitimate thing to check to see if its a valid credit card number though?

11

I don’t think so i just need to change the value of card_number somehow

12

and what do you have?

13

card_number = '4111-1111-4555-1141' within the main function which is what i don’t get becuause it tells me to change the value even though the value is what it is telling me

14

Really, because in the code you posted it’s:

Did you change anything else? Please repost your full function code.

15 
def verify_card_number(card_number):
    sum_of_odd_digits = 0
    card_number_reversed = card_number[::-1]
    odd_digits = card_number_reversed[::2]

    for digit in odd_digits:
        sum_of_odd_digits += int(digit)

    sum_of_even_digits = 0
    even_digits = card_number_reversed[1::2]
    for digit in even_digits:
        number = int(digit) * 2
        if number >= 10:
            number = (number // 10) + (number % 10)
        sum_of_even_digits += number
    total = sum_of_odd_digits + sum_of_even_digits
    print(total)
    return total % 10 == 0

# User Editable Region

def main():
    card_number = '4111-1111-4555-1142'
    card_translation = str.maketrans({'-': '', ' ': ''})
    translated_card_number = card_number.translate(card_translation)

# User Editable Region


    if verify_card_number(translated_card_number):
        print('VALID!')
    else:
        print('INVALID!')

main()
16

Looks different to me :face_with_monocle:

17

thank you so much i don’t actually know how i missed that to be honest

18

Read all the errors and hints carefully, they often contain exactly what you need :+1:

19

that doesn’t look like a card number at all, there card_number is None because that is the output of print