code: def get_graph(self, run_key, device_name, debug=False):
      
      return self.get_graphs(run_key, debug=debug).get(device_name, None)
docs: Get the runtime GraphDef proto associated with a run key and a device.
  
      Args:
        run_key: A Session.run kay.
        device_name: Name of the device in question.
        debug: Whether the debugger-decoratedgraph is to be retrieved.
  
      Returns:
        A `GraphDef` proto.