# damm.py - functions for performing the Damm checksum algorithm
#
# Copyright (C) 2016-2017 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 Damm algorithm.
The Damm algorithm is a check digit algorithm that should detect all
single-digit errors and all adjacent transposition errors. Based on
anti-symmetric quasigroup of order 10 it uses a substitution table.
This implementation uses the table from Wikipedia by default but a custom
table can be provided.
More information:
* https://en.wikipedia.org/wiki/Damm_algorithm
>>> validate('572')
Traceback (most recent call last):
...
InvalidChecksum: ...
>>> calc_check_digit('572')
'4'
>>> validate('5724')
'5724'
>>> table = (
... (0, 2, 3, 4, 5, 6, 7, 8, 9, 1),
... (2, 0, 4, 1, 7, 9, 5, 3, 8, 6),
... (3, 7, 0, 5, 2, 8, 1, 6, 4, 9),
... (4, 1, 8, 0, 6, 3, 9, 2, 7, 5),
... (5, 6, 2, 9, 0, 7, 4, 1, 3, 8),
... (6, 9, 7, 3, 1, 0, 8, 5, 2, 4),
... (7, 5, 1, 8, 4, 2, 0, 9, 6, 3),
... (8, 4, 6, 2, 9, 5, 3, 0, 1, 7),
... (9, 8, 5, 7, 3, 1, 6, 4, 0, 2),
... (1, 3, 9, 6, 8, 4, 2, 7, 5, 0))
>>> checksum('816', table=table)
9
"""
from stdnum.exceptions import *
_operation_table = (
(0, 3, 1, 7, 5, 9, 8, 6, 4, 2),
(7, 0, 9, 2, 1, 5, 4, 8, 6, 3),
(4, 2, 0, 6, 8, 7, 1, 3, 5, 9),
(1, 7, 5, 0, 9, 8, 3, 4, 2, 6),
(6, 1, 2, 3, 0, 4, 5, 9, 7, 8),
(3, 6, 7, 4, 2, 0, 9, 5, 8, 1),
(5, 8, 6, 9, 7, 2, 0, 1, 3, 4),
(8, 9, 4, 5, 3, 6, 2, 0, 1, 7),
(9, 4, 3, 8, 6, 1, 7, 2, 0, 5),
(2, 5, 8, 1, 4, 3, 6, 7, 9, 0))
def checksum(number, table=None):
"""Calculate the Damm checksum over the provided number. The checksum is
returned as an integer value and should be 0 when valid."""
table = table or _operation_table
i = 0
for n in str(number):
i = table[i][int(n)]
return i
def validate(number, table=None):
"""Check if the number provided passes the Damm algorithm."""
if not bool(number):
raise InvalidFormat()
try:
valid = checksum(number, table=table) == 0
except Exception:
raise InvalidFormat()
if not valid:
raise InvalidChecksum()
return number
def is_valid(number, table=None):
"""Check if the number provided passes the Damm algorithm."""
try:
return bool(validate(number, table=table))
except ValidationError:
return False
def calc_check_digit(number, table=None):
"""Calculate the extra digit that should be appended to the number to
make it a valid number."""
return str(checksum(number, table=table))