76 lines
2.5 KiB
Python
76 lines
2.5 KiB
Python
# mod_37_36.py - functions for performing the ISO 7064 Mod 37, 36 algorithm
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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 ISO 7064 Mod 37, 36 algorithm.
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The Mod 37, 36 algorithm uses an alphanumeric check digit and the number
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itself may also contain letters.
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>>> checksum('A12425GABC1234002M')
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1
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>>> calc_check_digit('A12425GABC1234002')
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'M'
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>>> validate('A12425GABC1234002M')
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'A12425GABC1234002M'
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By changing the alphabet this can be turned into any Mod x+1, x
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algorithm. For example Mod 11, 10:
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>>> calc_check_digit('00200667308', alphabet='0123456789')
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'5'
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>>> validate('002006673085', alphabet='0123456789')
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'002006673085'
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"""
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from stdnum.exceptions import *
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def checksum(number, alphabet='0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ'):
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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 = modulus // 2
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for n in number:
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check = (((check or modulus) * 2) % (modulus + 1) + alphabet.index(n)) % modulus
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return check
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def calc_check_digit(number, alphabet='0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ'):
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"""With the provided number, calculate the extra digit that should be
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appended to make it a valid number."""
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modulus = len(alphabet)
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return alphabet[(1 - ((checksum(number, alphabet) or modulus) * 2) % (modulus + 1)) % modulus]
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def validate(number, alphabet='0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ'):
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"""Checks 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:
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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, alphabet='0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ'):
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"""Checks 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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