docs: def get_constituency_extractor(self):
          """
          Returns a constituency extractor object
          @rtype: L{Cconstituency_extractor}
          @return: a constituency extractor object
          """
  
          if self.constituency_layer is not None:    ##Otherwise there are no constituens
              if self.my_constituency_extractor is None:
                  self.my_constituency_extractor = Cconstituency_extractor(self)
              return self.my_constituency_extractor
          else:
              return None