docs: def get_dependency_extractor(self):
          """
          Returns a dependency extractor object
          @rtype: L{Cdependency_extractor}
          @return: a dependency extractor object
          """
          if self.dependency_layer is not None:    #otherwise there are no dependencies
              if self.my_dependency_extractor is None:
                  self.my_dependency_extractor = Cdependency_extractor(self)
              return self.my_dependency_extractor
          else:
              return None