FreeCodeCamp

Learn How to Work with Numbers and Strings

5 snippets

Explain Each Step of the Luhn Algorithm in Comments

A commented version of the Luhn validator to explain how numbers and strings are processed.

def luhn_verbose(card_number): digits = [int(d) for d in str(card_number)][::-1] # reverse digits for i in range(1, len(digits), 2): # double every second digit doubled = digits[i] * 2 digits[i] = doubled if doubled < 10...

Generate a Random Valid Credit Card Number (Luhn-Compliant)

Use the Luhn algorithm to generate test card numbers for simulations.

import random def generate_card(): base = [random.randint(0, 9) for _ in range(15)] digits = base[::-1] for i in range(1, len(digits), 2): doubled = digits[i] * 2 digits[i] = doubled if doubled < 10 else doubled - 9 ...

Format Card Number as XXXX-XXXX-XXXX-XXXX

Write a helper function to format card numbers using string manipulation.

def format_card(number): s = str(number).replace(" ", "") return "-".join([s[i:i+4] for i in range(0, len(s), 4)])

Add a Check Digit to a Number Using Luhn Algorithm

Extend the Luhn logic to generate a valid check digit for any number.

def luhn_generate(number): digits = [int(d) for d in str(number)] digits.append(0) for i in range(len(digits) - 2, -1, -2): doubled = digits[i] * 2 digits[i] = doubled if doubled < 10 else doubled - 9 checksum =...

Validate a Credit Card Number Using the Luhn Algorithm

Build a function that takes a number as input and checks if it passes the Luhn checksum validation.

def luhn_check(card_number): digits = [int(d) for d in str(card_number)][::-1] for i in range(1, len(digits), 2): doubled = digits[i] * 2 digits[i] = doubled if doubled < 10 else doubled - 9 return sum(digits) % 10 == 0