app/django/utils/checksums.py
author James Levy <jamesalexanderlevy@gmail.com>
Sat, 04 Jul 2009 13:53:17 +0200
changeset 2526 8f29bfb9eb52
parent 54 03e267d67478
permissions -rw-r--r--
Survey editing/taking Javascript and CSS fixes. This patch adds some cosmetic changes and functional fixes: - UI now removes all of the field content when a field is deleted, - CSS tweaks, and jQuery hack to specialize comment CSS, - fixed JS path in take.html. Reviewed by: Pawel Solyga (with some small changes)

"""
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