app/django/utils/checksums.py
author Lennard de Rijk <ljvderijk@gmail.com>
Fri, 03 Jul 2009 15:00:00 +0200
changeset 2506 c98bf890156e
parent 54 03e267d67478
permissions -rw-r--r--
Removed getSurveyResponseFromPost from Surveys helper. We will use the power of Django Forms instead of getting our own properties. This fits better into the rest of Melange which also uses this approach.

"""
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