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Credit card validation is a crucial task in various financial and e-commerce applications. One of the most common algorithms used for this purpose is the Luhn algorithm. In this tutorial, I will cover how to validate a credit card number using the Luhn algorithm, detect the card type, and handle multiple card numbers from a file using Python.
The Luhn algorithm, also known as the "modulus 10" or "mod 10" algorithm, is a simple checksum formula used to validate various identification numbers. It is designed to protect against accidental errors, such as a single digit being mistyped or some digits being transposed.
Example Credit Card Number: 5555 5555 5555 4444 (Mastercard's actual test number)
Since the total modulo 10 is 0, the credit card number 5555 5555 5555 4444 is valid according to the Luhn algorithm.
We'll be making use of Python 3. No need to install any package, as the ones we'll be using come pre-installed with Python. Open up a Python file, name it meaningfully, like credit_card_validation.py
and follow along:
We started by importing re
for using regular expressions (we'll use them to determine what kind of card it is) and argparse
for getting user arguments from the command line. Then, we created a function to implement Luhn's algorithm.
Next, we'll create two functions. One is for checking a credit card number using the Luhn algorithm (from the function above), and the other is to get the credit card type based on the number:
The card_types
dictionary in the get_card_type()
function defines regular expressions (regex patterns) to identify different credit card types based on their starting digits and length:
Each regex pattern is designed to match specific starting sequences and digit lengths unique to each card type.
Note: I haven't tested all the card types. I used GPT-4o to get the formats of each card type and did the regular expressions for them. But for the three I've tested, they're very correct. I am telling you this in case you encounter an issue (which I doubt). The idea is just to know the pattern of a particular card type, and integrate using regular expressions.
Moving on, because we want to make our program very sophisticated, we'll add functionality to accept a text file (optionally) containing credit card numbers instead of typing them one after the other:
Finally, we create the main function. Here, we'll use argparse
to accept user arguments and handle overall program execution:
The main
function handles input from either a single credit card number or a file with multiple credit card numbers, validates each number using the Luhn algorithm, identifies the card type, and prints the results.
Let's start by running our program using just one credit card:
Result:
And yes, 5555555555554444 is a Mastercard number. It is Mastercard's test number.
Screenshot:
Next, we try running the program with a txt file:
Result:
Screenshot:
Note: These numbers are all test numbers for the various card types. Feel free to try with your own cards.
In this tutorial, you've learned about the Luhn algorithm and how to use it to validate CC numbers and determine the card type based on patterns.
I hope you enjoyed this one, till next time! You can get the complete code here.
Related: How to Generate Fake User Data in Python
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