code: def add_graph(self, other):
          
          self.add_nodes( n for n in other.nodes() if not n in self.nodes() )
          
          for each_node in other.nodes():
              for each_edge in other.neighbors(each_node):
                  if (not self.has_edge((each_node, each_edge))):
                      self.add_edge((each_node, each_edge))
docs: Add other graph to this graph.
          
          @attention: Attributes and labels are not preserved.
          
          @type  other: graph
          @param other: Graph