code: def graph_to_dot(graph, node_renderer=None, edge_renderer=None):
      
      node_pairs = list(graph.nodes.items())
      edge_pairs = list(graph.edges.items())
  
      if node_renderer is None:
          node_renderer_wrapper = lambda nid: ''
      else:
          node_renderer_wrapper = lambda nid: ' [%s]' % ','.join(
              ['%s=%s' % tpl for tpl in list(node_renderer(graph, nid).items())])
  
      # Start the graph
      graph_string = 'digraph G {\n'
      graph_string += 'overlap=scale;\n'
  
      # Print the nodes (placeholder)
      for node_id, node in node_pairs:
          graph_string += '%i%s;\n' % (node_id, node_renderer_wrapper(node_id))
  
      # Print the edges
      for edge_id, edge in edge_pairs:
          node_a = edge['vertices'][0]
          node_b = edge['vertices'][1]
          graph_string += '%i -> %i;\n' % (node_a, node_b)
  
      # Finish the graph
      graph_string += '}'
  
      return graph_string
docs: Produces a DOT specification string from the provided graph.