code: def preprocess_for_pydot(docgraph):
      
      stripped_graph = nx.MultiDiGraph()
      stripped_graph.name = docgraph.name
  
      nodes = _preprocess_nodes_for_pydot(docgraph.nodes_iter(data=True))
      edges = _preprocess_edges_for_pydot(docgraph.edges_iter(data=True))
  
      stripped_graph.add_nodes_from(nodes)
      stripped_graph.add_edges_from(edges)
      return stripped_graph
docs: takes a document graph and strips all the information that aren't
      necessary for visualizing it with graphviz. ensures that all
      node/edge names and labels are properly quoted.
  
      Parameters
      ----------
      docgraph : DiscourseDocumentGraph
          a document graph
      Returns
      -------
      stripped_graph : networkx.MultiDiGraph
          a graph containing only information that is needed for graphviz