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Shared/lib/python3.4/site-packages/stdnum/verhoeff.py

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+# verhoeff.py - functions for performing the Verhoeff checksum
+#
+# Copyright (C) 2010, 2011, 2012, 2013 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 Verhoeff algorithm.
+
+The Verhoeff algorithm uses two tables for permutations and
+multiplications to calculate a checksum.
+
+>>> validate('1234')
+Traceback (most recent call last):
+    ...
+InvalidChecksum: ...
+>>> checksum('1234')
+1
+>>> calc_check_digit('1234')
+'0'
+>>> validate('12340')
+'12340'
+"""
+
+from stdnum.exceptions import *
+
+
+# These are the multiplication and permutation tables used in the
+# Verhoeff algorithm.
+
+_multiplication_table = (
+    [0, 1, 2, 3, 4, 5, 6, 7, 8, 9],
+    [1, 2, 3, 4, 0, 6, 7, 8, 9, 5],
+    [2, 3, 4, 0, 1, 7, 8, 9, 5, 6],
+    [3, 4, 0, 1, 2, 8, 9, 5, 6, 7],
+    [4, 0, 1, 2, 3, 9, 5, 6, 7, 8],
+    [5, 9, 8, 7, 6, 0, 4, 3, 2, 1],
+    [6, 5, 9, 8, 7, 1, 0, 4, 3, 2],
+    [7, 6, 5, 9, 8, 2, 1, 0, 4, 3],
+    [8, 7, 6, 5, 9, 3, 2, 1, 0, 4],
+    [9, 8, 7, 6, 5, 4, 3, 2, 1, 0])
+
+_permutation_table = (
+    (0, 1, 2, 3, 4, 5, 6, 7, 8, 9),
+    (1, 5, 7, 6, 2, 8, 3, 0, 9, 4),
+    (5, 8, 0, 3, 7, 9, 6, 1, 4, 2),
+    (8, 9, 1, 6, 0, 4, 3, 5, 2, 7),
+    (9, 4, 5, 3, 1, 2, 6, 8, 7, 0),
+    (4, 2, 8, 6, 5, 7, 3, 9, 0, 1),
+    (2, 7, 9, 3, 8, 0, 6, 4, 1, 5),
+    (7, 0, 4, 6, 9, 1, 3, 2, 5, 8))
+
+
+def checksum(number):
+    """Calculate the Verhoeff checksum over the provided number. The checksum
+    is returned as an int. Valid numbers should have a checksum of 0."""
+    # transform number list
+    number = tuple(int(n) for n in reversed(str(number)))
+    # calculate checksum
+    check = 0
+    for i, n in enumerate(number):
+        check = _multiplication_table[check][_permutation_table[i % 8][n]]
+    return check
+
+
+def validate(number):
+    """Checks to see if the number provided passes the Verhoeff checksum."""
+    if not bool(number):
+        raise InvalidFormat()
+    try:
+        valid = checksum(number) == 0
+    except:
+        raise InvalidFormat()
+    if not valid:
+        raise InvalidChecksum()
+    return number
+
+
+def is_valid(number):
+    """Checks to see if the number provided passes the Verhoeff checksum."""
+    try:
+        return bool(validate(number))
+    except ValidationError:
+        return False
+
+
+def calc_check_digit(number):
+    """With the provided number, calculate the extra digit that should be
+    appended to make it pass the Verhoeff checksum."""
+    return str(_multiplication_table[checksum(str(number) + '0')].index(0))