app/django/utils/checksums.py
author Todd Larsen <tlarsen@google.com>
Fri, 18 Jul 2008 18:38:41 +0000
changeset 57 e30229fd9add
parent 54 03e267d67478
permissions -rw-r--r--
HTML mockups of proposed Melange (generic), GSoC, and GHOP pages and forms. The HTML files in this directory are formatted to be viewed directly from svn via http://soc.googlecode.com/svn/trunk/mockups/. All of the paths will be relative (rooted at /svn/trunk/mockups/) and instructions will be added (in a mockups/README file) for configuring an Apache web server for previewing the pages from the svn working copy during development.

"""
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