code: def generators(self):
          
          if not self._generators:
              generators = list(self.graph.nodes_by_attribute('generator'))
              generators.extend(list(self.graph.nodes_by_attribute(
                  'generator_aggr')))
              return generators
          else:
              return self._generators
docs: Connected Generators within the grid
  
          Returns
          -------
          list
              List of Generator Objects