/bangkokhotel/lib/python2.5/site-packages/django/utils/checksums.py

 1"""
 2Common checksum routines (used in multiple localflavor/ cases, for example).
 3"""
 4
 5__all__ = ['luhn',]
 6
 7LUHN_ODD_LOOKUP = (0, 2, 4, 6, 8, 1, 3, 5, 7, 9) # sum_of_digits(index * 2)
 8
 9def luhn(candidate):
10    """
11    Checks a candidate number for validity according to the Luhn
12    algorithm (used in validation of, for example, credit cards).
13    Both numeric and string candidates are accepted.
14    """
15    if not isinstance(candidate, basestring):
16        candidate = str(candidate)
17    try:
18        evens = sum([int(c) for c in candidate[-1::-2]])
19        odds = sum([LUHN_ODD_LOOKUP[int(c)] for c in candidate[-2::-2]])
20        return ((evens + odds) % 10 == 0)
21    except ValueError:  # Raised if an int conversion fails
22        return False