old_contents: # issn.py - functions for handling ISSNs
  #
  # Copyright (C) 2010 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
  
  """Module for handling ISSNs (International Standard Serial Number), the
  standard code to identify serial publications.
  
  >>> is_valid('0024-9319')
  True
  >>> is_valid('0032147X') # incorrect check digit
  False
  >>> compact('0032-1478')
  '00321478'
  >>> format('00249319')
  '0024-9319'
  """
  
  
  def compact(number):
      """Convert the ISSN to the minimal representation. This strips the number
      of any valid ISSN separators and removes surrounding whitespace."""
      number = number.replace(' ','').replace('-','').strip().upper()
      return number
  
  def _calc_check_digit(number):
      """Calculate the ISSN check digit for 10-digit numbers. The number passed
      should not have the check bit included."""
      check = (11 - sum( (8 - i) * int(n) for i, n in enumerate(number) ) ) % 11
      return 'X' if check == 10 else str(check)
  
  def is_valid(number):
      """Checks to see if the number provided is a valid ISSN. This checks
      the length and whether the check digit is correct."""
      try:
          number = compact(number)
      except:
          return False
      return len(number) == 8 and \
             number[:-1].isdigit() and \
             _calc_check_digit(number[:-1]) == number[-1]
  
  def format(number):
      """Reformat the passed number to the standard format."""
      number = compact(number)
      return number[:4] + '-' + number[4:]
  
new_contents: # issn.py - functions for handling ISSNs
  #
  # Copyright (C) 2010 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
  
  """Module for handling ISSNs (International Standard Serial Number), the
  standard code to identify serial publications.
  
  >>> is_valid('0024-9319')
  True
  >>> is_valid('0032147X') # incorrect check digit
  False
  >>> compact('0032-1478')
  '00321478'
  >>> format('00249319')
  '0024-9319'
  >>> to_ean('0264-3596')
  '9770264359008'
  """
  
  from stdnum import ean
  
  
  def compact(number):
      """Convert the ISSN to the minimal representation. This strips the number
      of any valid ISSN separators and removes surrounding whitespace."""
      number = number.replace(' ','').replace('-','').strip().upper()
      return number
  
  def _calc_check_digit(number):
      """Calculate the ISSN check digit for 10-digit numbers. The number passed
      should not have the check bit included."""
      check = (11 - sum( (8 - i) * int(n) for i, n in enumerate(number) ) ) % 11
      return 'X' if check == 10 else str(check)
  
  def is_valid(number):
      """Checks to see if the number provided is a valid ISSN. This checks
      the length and whether the check digit is correct."""
      try:
          number = compact(number)
      except:
          return False
      return len(number) == 8 and \
             number[:-1].isdigit() and \
             _calc_check_digit(number[:-1]) == number[-1]
  
  def format(number):
      """Reformat the passed number to the standard format."""
      number = compact(number)
      return number[:4] + '-' + number[4:]
  
  def to_ean(number, issue_code='00'):
      """Convert the number to EAN-13 format. The number is assumed to be a
      valid ISSN."""
      number = '977' + compact(number)[:-1] + issue_code
      return number + ean.calc_check_digit(number)
  
subject: implement a conversion function from ISSN to EAN