Source code for localflavor.generic.checksums

"""
Common checksum routines.
"""
from django.utils import six

__all__ = ['luhn', 'ean']

LUHN_ODD_LOOKUP = (0, 2, 4, 6, 8, 1, 3, 5, 7, 9)  # sum_of_digits(index * 2)
EAN_LOOKUP = (3, 1)


[docs]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, six.string_types): 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
[docs]def ean(candidate): """ Checks a candidate number for validity according to the EAN checksum calculation. Note that this validator does not enforce any length checks (usually 13 or 8). http://en.wikipedia.org/wiki/International_Article_Number_(EAN) """ if not isinstance(candidate, six.string_types): candidate = str(candidate) if len(candidate) <= 1: return False given_number, given_checksum = candidate[:-1], candidate[-1] try: calculated_checksum = sum( int(digit) * EAN_LOOKUP[i % 2] for i, digit in enumerate(reversed(given_number))) calculated_checksum = 10 - (calculated_checksum % 10) return str(calculated_checksum) == given_checksum except ValueError: # Raised if an int conversion fails return False