diff --git a/README.md b/README.md
@@ -99,17 +99,22 @@ Most cards do not even use a 3rd track, and is mostly un-used worldwide.
| 9 | For assignment by national standards bodies *(next 3 digits are [ISO 3166-1](https://en.wikipedia.org/wiki/ISO_3166-1))* |
### Issuer Identification Number *(IIN)*
-| Issuer | INN Range | PAN Digits |
-| ------------------------- | ------------------------------- | ---------- |
-| American Express | 34-37 | 15 |
-| China Union Pay | 62 | 16-19 |
-| Diners Club International | 36, 38, 39, 309, 300-3005 | 14 |
-| Discover | 65, 644-649, 6011 622126-622925 | 16, 19 |
-| JCB | 3528-3589 | 16 |
-| Maestro | 50, 56-69 | 12-19 |
-| Mastercard | 51-55, 2221-2720 | 16 |
-| RuPay | 607 | 16 |
-| Visa | 4 | 12, 16, 19 |
+| Issuer | INN Range | PAN Digits |
+| ------------------------- | -------------------------------- | ---------- |
+| American Express | 34-37 | 15 |
+| China Union Pay | 62 | 16-19 |
+| Diners Club International | 36, 38, 39, 309, 300-3005 | 14 |
+| Discover | 65, 644-649, 6011, 622126-622925 | 16, 19 |
+| JCB | 3528-3589 | 16 |
+| Maestro | 50, 56-69 | 12-19 |
+| Mastercard | 51-55, 2221-2720 | 16 |
+| RuPay | 607 | 16 |
+| Visa | 4 | 12, 16, 19 |
+
+## Notes
+The [Luhn Algorithm](https://en.wikipedia.org/wiki/Luhn_algorithm) or modulo-10 Algorithm *([example python code](./luhn_algo.py))* is used to determine the last digit of the account number, also known as the Check Number.
+
+This number should be divisible by 10, hence "modulo-10" ;)
## References
- [Digital Card](https://en.wikipedia.org/wiki/Digital_card)
diff --git a/luhn_algo.py b/luhn_algo.py
@@ -0,0 +1,41 @@
+#!/usr/bin/env python
+# Luhn Algorithm Example - Developed by acidvegas in Python (https://git.acid.vegas/msr90)
+
+def modulus10(card_number: str) -> str:
+ '''
+ Validate a card number using the Luhn Algorithm
+
+ :param card_number: The card number to validate
+ '''
+
+ digits = [int(d) for d in card_number]
+ total_sum = 0
+ reversed_digits = digits[::-1]
+
+ for i in range(len(reversed_digits)):
+ digit = reversed_digits[i]
+
+ if i % 2 != 0:
+ digit = digit * 2
+
+ if digit > 9:
+ digit -= 9
+
+ total_sum += digit
+
+ check_digit = (10 - (total_sum % 10)) % 10
+ full_card_number = card_number + str(check_digit)
+
+ if (total_sum + check_digit) % 10 != 0:
+ raise ValueError('failed luhn check (non-divisible by 10)')
+
+ return full_card_number
+
+
+if __name__ == '__main__':
+ card_number = input('Enter your card number without the last digit:')
+
+ if not card_number.isdigit():
+ raise ValueError('invalid card number')
+
+ print(f'Full card number: {modulus10(card_number)}')
| |
