86 lines
2.7 KiB
Python
86 lines
2.7 KiB
Python
# luhn.py - functions for performing the Luhn and Luhn mod N algorithms
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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 Luhn and Luhn mod N algorithms.
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The Luhn algorithm is used to detect most accidental errors in various
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identification numbers.
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>>> validate('7894')
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Traceback (most recent call last):
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...
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InvalidChecksum: ...
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>>> checksum('7894')
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6
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>>> calc_check_digit('7894')
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'9'
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>>> validate('78949')
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'78949'
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An alternative alphabet can be provided to use the Luhn mod N algorithm.
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The default alphabet is '0123456789'.
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>>> validate('1234', alphabet='0123456789abcdef')
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Traceback (most recent call last):
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...
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InvalidChecksum: ...
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>>> checksum('1234', alphabet='0123456789abcdef')
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14
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"""
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from stdnum.exceptions import *
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def checksum(number, alphabet='0123456789'):
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"""Calculate the Luhn checksum over the provided number. The checksum
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is returned as an int. Valid numbers should have a checksum of 0."""
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n = len(alphabet)
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number = tuple(alphabet.index(i)
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for i in reversed(str(number)))
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return (sum(number[::2]) +
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sum(sum(divmod(i * 2, n))
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for i in number[1::2])) % n
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def validate(number, alphabet='0123456789'):
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"""Checks to see if the number provided passes the Luhn checksum."""
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if not bool(number):
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raise InvalidFormat()
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try:
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valid = checksum(number, alphabet) == 0
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except Exception:
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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='0123456789'):
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"""Checks to see if the number provided passes the Luhn checksum."""
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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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def calc_check_digit(number, alphabet='0123456789'):
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"""With the provided number, calculate the extra digit that should be
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appended to make it pass the Luhn checksum."""
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ck = checksum(str(number) + alphabet[0], alphabet)
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return alphabet[-ck]
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