# mod_11_2.py - functions for performing the ISO 7064 Mod 11, 2 algorithm # # 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 ISO 7064 Mod 11, 2 algorithm. The Mod 11, 2 algorithm is a simple module 11 checksum where the check digit can be an X to make the number valid. For a module that can do generic Mod x, 2 calculations see the :mod:`stdnum.iso7064.mod_37_2` module. >>> calc_check_digit('0794') '0' >>> validate('07940') '07940' >>> calc_check_digit('079') 'X' >>> validate('079X') '079X' >>> checksum('079X') 1 """ from stdnum.exceptions import * def checksum(number): """Calculate the checksum. A valid number should have a checksum of 1.""" check = 0 for n in number: check = (2 * check + int(10 if n == 'X' else n)) % 11 return check def calc_check_digit(number): """With the provided number, calculate the extra digit that should be appended to make it a valid number.""" c = (1 - 2 * checksum(number)) % 11 return 'X' if c == 10 else str(c) def validate(number): """Checks whether the check digit is valid.""" try: valid = checksum(number) == 1 except: raise InvalidFormat() if not valid: raise InvalidChecksum() return number def is_valid(number): """Checks whether the check digit is valid.""" try: return bool(validate(number)) except ValidationError: return False