app/django/utils/checksums.py
author Todd Larsen <tlarsen@google.com>
Fri, 19 Sep 2008 05:15:20 +0000
changeset 170 1fadf6e0348d
parent 54 03e267d67478
permissions -rw-r--r--
Add /site/user/profile Developer view for editing arbitrary User entities. Update /user/profile edit() view to fix TODO about updating the URL when a POST of the form changes the link_name of the User. Add a Create New User link to the base.html sidebar mock-up.

"""
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