def add_subgraph(self, sgraph):
if not isinstance(sgraph, Subgraph) and not isinstance(sgraph, Cluster):<EOL><INDENT>raise TypeError('<STR_LIT>' + str(sgraph))<EOL><DEDENT>if sgraph.get_name() in self.obj_dict['<STR_LIT>']:<EOL><INDENT>sgraph_list = self.obj_dict['<STR_LIT>'][ sgraph.get_name() ]<EOL>sgraph_list.append( sgraph.obj_dict )<EOL><DEDENT>else:<EOL><INDENT>self.obj_dict['<STR_LIT>'][ sgraph.get_name() ] = [ sgraph.obj_dict ]<EOL><DEDENT>sgraph.set_sequence( self.get_next_sequence_number() )<EOL>sgraph.set_parent_graph( self.get_parent_graph() )<EOL>
Adds an subgraph object to the graph.

        It takes a subgraph object as its only argument and returns
        None.