74 lines
2.1 KiB
Python
74 lines
2.1 KiB
Python
# mod_11_2.py - functions for performing the ISO 7064 Mod 11, 2 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 11, 2 algorithm.
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The Mod 11, 2 algorithm is a simple module 11 checksum where the check
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digit can be an X to make the number valid.
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For a module that can do generic Mod x, 2 calculations see the
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:mod:`stdnum.iso7064.mod_37_2` module.
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>>> calc_check_digit('0794')
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'0'
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>>> validate('07940')
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'07940'
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>>> calc_check_digit('079')
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'X'
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>>> validate('079X')
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'079X'
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>>> checksum('079X')
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1
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"""
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from stdnum.exceptions import *
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def checksum(number):
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"""Calculate the checksum. A valid number should have a checksum of 1."""
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check = 0
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for n in number:
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check = (2 * check + int(10 if n == 'X' else n)) % 11
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return check
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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 a valid number."""
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c = (1 - 2 * checksum(number)) % 11
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return 'X' if c == 10 else str(c)
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def validate(number):
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"""Checks whether the check digit is valid."""
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try:
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valid = checksum(number) == 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):
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"""Checks whether the check digit is valid."""
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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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