app/django/utils/checksums.py
author Lennard de Rijk <ljvderijk@gmail.com>
Thu, 04 Jun 2009 21:58:05 +0200
changeset 2384 71780864a5ed
parent 54 03e267d67478
permissions -rw-r--r--
Now showing link to edit the home page document on the home page. This will only show up if you have the right to edit the document. Update issue 271 Now also working for home pages.

"""
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