| """ |
| Common checksum routines (used in multiple localflavor/ cases, for example). |
| """ |
| |
| __all__ = ['luhn',] |
| |
| LUHN_ODD_LOOKUP = (0, 2, 4, 6, 8, 1, 3, 5, 7, 9) # sum_of_digits(index * 2) |
| |
| def luhn(candidate): |
| """ |
| Checks a candidate number for validity according to the Luhn |
| algorithm (used in validation of, for example, credit cards). |
| Both numeric and string candidates are accepted. |
| """ |
| if not isinstance(candidate, basestring): |
| candidate = str(candidate) |
| try: |
| evens = sum([int(c) for c in candidate[-1::-2]]) |
| odds = sum([LUHN_ODD_LOOKUP[int(c)] for c in candidate[-2::-2]]) |
| return ((evens + odds) % 10 == 0) |
| except ValueError: # Raised if an int conversion fails |
| return False |
