app/django/utils/checksums.py
author Lennard de Rijk <ljvderijk@gmail.com>
Sun, 12 Jul 2009 14:03:35 +0200
changeset 2610 95949d4c45d9
parent 54 03e267d67478
permissions -rw-r--r--
Add scope view for GradingSurveyGroup and set access checks. The access checks are now properly set for create, edit and show. To facilitate the scope view the access check have an extra check built in to ensure that a scope is actually present before cheking for an existing Program.

"""
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