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