Rename all nodes in the network from x to prefix_x.  If no prefix
        is given, use the name of the graph as the prefix.
        
        The purpose of this method is to make node names unique so that
        composing two graphs is well-defined.

def addNodeLabelPrefix(self, prefix=None, copy=False):
        '''
        Rename all nodes in the network from x to prefix_x.  If no prefix
        is given, use the name of the graph as the prefix.
        
        The purpose of this method is to make node names unique so that
        composing two graphs is well-defined.
        '''
        nxgraph = Topology.__relabel_graph(self.__nxgraph, prefix)
        if copy:
            newtopo = copy.deepcopy(self)
            newtopo.nxgraph = nxgraph
            return newtopo
        else:
            # looks like it was done in place
            self.__nxgraph = nxgraph