app/django/utils/checksums.py
author Pawel Solyga <Pawel.Solyga@gmail.com>
Tue, 31 Mar 2009 16:00:17 +0000
changeset 2041 9a9307b22312
parent 54 03e267d67478
permissions -rw-r--r--
Make invalid Student Proposals also accessible for Hosts, Mentors and Org admins. Previously only new and pending Student Proposals could be viewed. Patch by: Pawel Solyga Reviewed by: to-be-reviewed

"""
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