class_docstr: A directed graph that can easily be JSON serialized for visualization.
  
  When serializing, it generates the following fields:
    edge: The list of all serialized Edge instances.
    node: The list of all serialized Vertex instances.
docstr: Creates and returns a new vertex.
  
  Returns:
    A new Vertex instance with a unique index.
docstr_tok: ["Creates","and","returns","a","new","vertex",".","Returns",":","A","new","Vertex","instance","with","a","unique","index","."]
code: def new_vertex(self):
      """Creates and returns a new vertex.
  
      Returns:
        A new Vertex instance with a unique index.
      """
      vertex = Vertex(len(self.vertices))
      self.vertices.append(vertex)
      return vertex
  
file_path: tensor2tensor/tensor2tensor/insights/graph.py
label_desc: Use image node_id 2 for calling the Graph obj's underlying member method code with example usage: obj.new_vertex() and returns: vertex