81 lines
2.6 KiB
Python
81 lines
2.6 KiB
Python
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# mod_37_2.py - functions for performing the ISO 7064 Mod 37, 2 algorithm
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#
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# Copyright (C) 2010-2021 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 ISO 7064 Mod 37, 2 algorithm.
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The Mod 37, 2 checksum can be used for alphanumeric numbers and the check
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digit may also be numeric, a letter or '*'.
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>>> calc_check_digit('G123489654321')
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'Y'
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>>> validate('G123489654321Y')
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'G123489654321Y'
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>>> checksum('G123489654321Y')
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1
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By changing the alphabet this can be turned into any Mod x, 2
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algorithm. For example Mod 11, 2:
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>>> calc_check_digit('079', alphabet='0123456789X')
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'X'
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>>> validate('079X', alphabet='0123456789X')
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'079X'
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>>> checksum('079X', alphabet='0123456789X')
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1
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"""
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from __future__ import annotations
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from stdnum.exceptions import *
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def checksum(number: str, alphabet: str = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ*') -> int:
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"""Calculate the checksum. A valid number should have a checksum of 1."""
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modulus = len(alphabet)
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check = 0
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for n in number:
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check = (2 * check + alphabet.index(n)) % modulus
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return check
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def calc_check_digit(number: str, alphabet: str = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ*') -> str:
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"""Calculate the extra digit that should be appended to the number to
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make it a valid number."""
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modulus = len(alphabet)
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return alphabet[(1 - 2 * checksum(number, alphabet)) % modulus]
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def validate(number: str, alphabet: str = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ*') -> str:
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"""Check whether the check digit is valid."""
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try:
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valid = checksum(number, alphabet) == 1
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except Exception: # noqa: B902
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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: str, alphabet: str = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ*') -> bool:
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"""Check whether the check digit is valid."""
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try:
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return bool(validate(number, alphabet))
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except ValidationError:
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return False
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