code: def _getMultigraphID(self, graph_name, subgraph_name=None):
          
          if self.isMultiInstance and self._instanceName is not None:
              if subgraph_name is None:
                  return "%s_%s" % (graph_name, self._instanceName)
              else:
                  return "%s_%s.%s_%s" % (graph_name, self._instanceName, 
                                          subgraph_name, self._instanceName)
          else:
              if subgraph_name is None:
                  return graph_name
              else:
                  return "%s.%s" % (graph_name, subgraph_name)
docs: Private method for generating Multigraph ID from graph name and 
          subgraph name. 
          
          @param  graph_name:     Graph Name.
          @param  subgraph_name:  Subgraph Name.
          @return:                Multigraph ID.