code: def isbn10(self):
          '''
          Encode ISBN number in ISBN10 format
          Raises exception if Bookland number different from 978
          @rtype:  string
          @return: ISBN formated as ISBN10
          '''
          if self._id[0:3] != '978':
              raise ISBNError("Invalid Bookland code: {}".format(self._id[0:3]))
          digit10 = _digit10(self._id[3:12])
          if digit10 == 10:
              return self._id[3:12] + 'X'
          else:
              return self._id[3:12] + str(digit10f isbn10(self):
          '''
          Encode ISBN number in ISBN10 format
          Raises exception if Bookland number different from 978
          @rtype:  string
          @return: ISBN formated as ISBN10
          '''
          if self._id[0:3] != '978':
              raise ISBNError("Invalid Bookland code: {}".format(self._id[0:3]))
          digit10 = _digit10(self._id[3:12])
          if digit10 == 10:
              return self._id[3:12] + 'X'
          else:
              return self._id[3:12] + str(digit10)
docs: Encode ISBN number in ISBN10 format
          Raises exception if Bookland number different from 978
          @rtype:  string
          @return: ISBN formated as ISBN10