114 lines
3.6 KiB
Python
114 lines
3.6 KiB
Python
# damm.py - functions for performing the Damm checksum algorithm
|
|
#
|
|
# Copyright (C) 2016-2021 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 __future__ import annotations
|
|
|
|
from stdnum.exceptions import *
|
|
|
|
|
|
TYPE_CHECKING = False
|
|
if TYPE_CHECKING: # pragma: no cover (only used when type checking)
|
|
from collections.abc import Sequence
|
|
DammTable = Sequence[Sequence[int]]
|
|
|
|
|
|
_operation_table: DammTable = (
|
|
(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: str, table: DammTable | None = None) -> int:
|
|
"""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: str, table: DammTable | None = None) -> str:
|
|
"""Check if the number provided passes the Damm algorithm."""
|
|
if not bool(number):
|
|
raise InvalidFormat()
|
|
try:
|
|
valid = checksum(number, table=table) == 0
|
|
except Exception: # noqa: B902
|
|
raise InvalidFormat()
|
|
if not valid:
|
|
raise InvalidChecksum()
|
|
return number
|
|
|
|
|
|
def is_valid(number: str, table: DammTable | None = None) -> bool:
|
|
"""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: str, table: DammTable | None = None) -> str:
|
|
"""Calculate the extra digit that should be appended to the number to
|
|
make it a valid number."""
|
|
return str(checksum(number, table=table))
|