def _getMultigraphID(self, graph_name, subgraph_name=None):
if self.isMultiInstance and self._instanceName is not None:<EOL><INDENT>if subgraph_name is None:<EOL><INDENT>return "<STR_LIT>" % (graph_name, self._instanceName)<EOL><DEDENT>else:<EOL><INDENT>return "<STR_LIT>" % (graph_name, self._instanceName, <EOL>subgraph_name, self._instanceName)<EOL><DEDENT><DEDENT>else:<EOL><INDENT>if subgraph_name is None:<EOL><INDENT>return graph_name<EOL><DEDENT>else:<EOL><INDENT>return "<STR_LIT>" % (graph_name, subgraph_name)<EOL><DEDENT><DEDENT>
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.