103 lines
3.1 KiB
Python
103 lines
3.1 KiB
Python
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# verhoeff.py - functions for performing the Verhoeff checksum
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#
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# Copyright (C) 2010, 2011, 2012, 2013 Arthur de Jong
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#
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# This library is free software; you can redistribute it and/or
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# modify it under the terms of the GNU Lesser General Public
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# License as published by the Free Software Foundation; either
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# version 2.1 of the License, or (at your option) any later version.
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#
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# This library is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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# Lesser General Public License for more details.
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#
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# You should have received a copy of the GNU Lesser General Public
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# License along with this library; if not, write to the Free Software
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# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
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# 02110-1301 USA
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"""The Verhoeff algorithm.
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The Verhoeff algorithm uses two tables for permutations and
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multiplications to calculate a checksum.
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>>> validate('1234')
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Traceback (most recent call last):
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...
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InvalidChecksum: ...
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>>> checksum('1234')
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1
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>>> calc_check_digit('1234')
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'0'
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>>> validate('12340')
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'12340'
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"""
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from stdnum.exceptions import *
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# These are the multiplication and permutation tables used in the
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# Verhoeff algorithm.
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_multiplication_table = (
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[0, 1, 2, 3, 4, 5, 6, 7, 8, 9],
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[1, 2, 3, 4, 0, 6, 7, 8, 9, 5],
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[2, 3, 4, 0, 1, 7, 8, 9, 5, 6],
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[3, 4, 0, 1, 2, 8, 9, 5, 6, 7],
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[4, 0, 1, 2, 3, 9, 5, 6, 7, 8],
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[5, 9, 8, 7, 6, 0, 4, 3, 2, 1],
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[6, 5, 9, 8, 7, 1, 0, 4, 3, 2],
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[7, 6, 5, 9, 8, 2, 1, 0, 4, 3],
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[8, 7, 6, 5, 9, 3, 2, 1, 0, 4],
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[9, 8, 7, 6, 5, 4, 3, 2, 1, 0])
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_permutation_table = (
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(0, 1, 2, 3, 4, 5, 6, 7, 8, 9),
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(1, 5, 7, 6, 2, 8, 3, 0, 9, 4),
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(5, 8, 0, 3, 7, 9, 6, 1, 4, 2),
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(8, 9, 1, 6, 0, 4, 3, 5, 2, 7),
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(9, 4, 5, 3, 1, 2, 6, 8, 7, 0),
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(4, 2, 8, 6, 5, 7, 3, 9, 0, 1),
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(2, 7, 9, 3, 8, 0, 6, 4, 1, 5),
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(7, 0, 4, 6, 9, 1, 3, 2, 5, 8))
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def checksum(number):
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"""Calculate the Verhoeff checksum over the provided number. The checksum
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is returned as an int. Valid numbers should have a checksum of 0."""
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# transform number list
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number = tuple(int(n) for n in reversed(str(number)))
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# calculate checksum
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check = 0
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for i, n in enumerate(number):
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check = _multiplication_table[check][_permutation_table[i % 8][n]]
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return check
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def validate(number):
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"""Checks to see if the number provided passes the Verhoeff checksum."""
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if not bool(number):
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raise InvalidFormat()
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try:
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valid = checksum(number) == 0
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except:
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raise InvalidFormat()
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if not valid:
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raise InvalidChecksum()
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return number
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def is_valid(number):
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"""Checks to see if the number provided passes the Verhoeff checksum."""
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try:
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return bool(validate(number))
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except ValidationError:
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return False
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def calc_check_digit(number):
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"""With the provided number, calculate the extra digit that should be
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appended to make it pass the Verhoeff checksum."""
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return str(_multiplication_table[checksum(str(number) + '0')].index(0))
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