app/django/utils/checksums.py
author Daniel Bentley <dbentley@google.com>
Sun, 12 Apr 2009 09:06:45 +0000
changeset 2168 ef7222d4847f
parent 54 03e267d67478
permissions -rw-r--r--
Use offset_linkid instead of offset to scan >1000 entities. this is a first-cut. It works in all the ways I could make earlier versions fail. It passes link_id as URL parameters. It also has a new class LinkCreator which makes the main body of getListContents even easier to write. I wasn't sure if link_id's could have non alphanumeric characters; if so, they need to be URL encoded/decoded. I also need to go and remove any mention of raw offsets now, because we don't use them. I believe I've talked about this approach with a few of you and it sounded reasonable. Feel free to roll-back/fix/amend/comment-for-me-to-fix. This is my first big-logic-change to Melange. Patch by: Dan Bentley

"""
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