code: def doi(self):
          '''
          Returns ISBN number with segment hypenation
          Data obtained from https://www.isbn-international.org/
          https://www.isbn-international.org/export_rangemessage.xml
          @return: ISBN formated as ISBN13 with hyphens
          '''
          if not ISBN.hyphenRange:
              ISBN.hyphenRange = hyphen.ISBNRange()
  
          seg = ISBN.hyphenRange.hyphensegments(self._id)
          return '10.' + self._id[0:3] + '.' + \
              self._id[3:-(1 + seg[3])] + '/' + self._id[-(1 + seg[3]):f doi(self):
          '''
          Returns ISBN number with segment hypenation
          Data obtained from https://www.isbn-international.org/
          https://www.isbn-international.org/export_rangemessage.xml
          @return: ISBN formated as ISBN13 with hyphens
          '''
          if not ISBN.hyphenRange:
              ISBN.hyphenRange = hyphen.ISBNRange()
  
          seg = ISBN.hyphenRange.hyphensegments(self._id)
          return '10.' + self._id[0:3] + '.' + \
              self._id[3:-(1 + seg[3])] + '/' + self._id[-(1 + seg[3]):]
docs: Returns ISBN number with segment hypenation
          Data obtained from https://www.isbn-international.org/
          https://www.isbn-international.org/export_rangemessage.xml
          @return: ISBN formated as ISBN13 with hyphens