87 lines
2.7 KiB
Python
87 lines
2.7 KiB
Python
|
# luhn.py - functions for performing the Luhn and Luhn mod N algorithms
|
||
|
|
#
|
||
|
|
# Copyright (C) 2010, 2011, 2012, 2013 Arthur de Jong
|
||
|
|
#
|
||
|
|
# This library is free software; you can redistribute it and/or
|
||
|
|
# modify it under the terms of the GNU Lesser General Public
|
||
|
|
# License as published by the Free Software Foundation; either
|
||
|
|
# version 2.1 of the License, or (at your option) any later version.
|
||
|
|
#
|
||
|
|
# This library is distributed in the hope that it will be useful,
|
||
|
|
# but WITHOUT ANY WARRANTY; without even the implied warranty of
|
||
|
|
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
|
||
|
|
# Lesser General Public License for more details.
|
||
|
|
#
|
||
|
|
# You should have received a copy of the GNU Lesser General Public
|
||
|
|
# License along with this library; if not, write to the Free Software
|
||
|
|
# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
|
||
|
|
# 02110-1301 USA
|
||
|
|
|
||
|
|
"""The Luhn and Luhn mod N algorithms.
|
||
|
|
|
||
|
|
The Luhn algorithm is used to detect most accidental errors in various
|
||
|
|
identification numbers.
|
||
|
|
|
||
|
|
>>> validate('7894')
|
||
|
|
Traceback (most recent call last):
|
||
|
|
...
|
||
|
|
InvalidChecksum: ...
|
||
|
|
>>> checksum('7894')
|
||
|
|
6
|
||
|
|
>>> calc_check_digit('7894')
|
||
|
|
'9'
|
||
|
|
>>> validate('78949')
|
||
|
|
'78949'
|
||
|
|
|
||
|
|
An alternative alphabet can be provided to use the Luhn mod N algorithm.
|
||
|
|
The default alphabet is '0123456789'.
|
||
|
|
|
||
|
|
>>> validate('1234', alphabet='0123456789abcdef')
|
||
|
|
Traceback (most recent call last):
|
||
|
|
...
|
||
|
|
InvalidChecksum: ...
|
||
|
|
>>> checksum('1234', alphabet='0123456789abcdef')
|
||
|
|
14
|
||
|
|
"""
|
||
|
|
|
||
|
|
from stdnum.exceptions import *
|
||
|
|
|
||
|
|
|
||
|
|
def checksum(number, alphabet='0123456789'):
|
||
|
|
"""Calculate the Luhn checksum over the provided number. The checksum
|
||
|
|
is returned as an int. Valid numbers should have a checksum of 0."""
|
||
|
|
n = len(alphabet)
|
||
|
|
number = tuple(alphabet.index(i)
|
||
|
|
for i in reversed(str(number)))
|
||
|
|
return (sum(number[::2]) +
|
||
|
|
sum(sum(divmod(i * 2, n))
|
||
|
|
for i in number[1::2])) % n
|
||
|
|
|
||
|
|
|
||
|
|
def validate(number, alphabet='0123456789'):
|
||
|
|
"""Checks to see if the number provided passes the Luhn checksum."""
|
||
|
|
if not bool(number):
|
||
|
|
raise InvalidFormat()
|
||
|
|
try:
|
||
|
|
valid = checksum(number, alphabet) == 0
|
||
|
|
except:
|
||
|
|
raise InvalidFormat()
|
||
|
|
if not valid:
|
||
|
|
raise InvalidChecksum()
|
||
|
|
return number
|
||
|
|
|
||
|
|
|
||
|
|
def is_valid(number, alphabet='0123456789'):
|
||
|
|
"""Checks to see if the number provided passes the Luhn checksum."""
|
||
|
|
try:
|
||
|
|
return bool(validate(number, alphabet))
|
||
|
|
except ValidationError:
|
||
|
|
return False
|
||
|
|
|
||
|
|
|
||
|
|
def calc_check_digit(number, alphabet='0123456789'):
|
||
|
|
"""With the provided number, calculate the extra digit that should be
|
||
|
|
appended to make it pass the Luhn checksum."""
|
||
|
|
ck = checksum(str(number) + alphabet[0], alphabet)
|
||
|
|
return alphabet[-ck]
|