code: def _load_graphdef_protobuf(handle, **kwargs):
      
      # as_graph_def
      graph_def = tf.GraphDef.FromString(handle.read())
  
      # check if this is a lucid-saved model
      # metadata = modelzoo.util.extract_metadata(graph_def)
      # if metadata is not None:
      #   url = handle.name
      #   return modelzoo.vision_base.Model.load_from_metadata(url, metadata)
  
      # else return a normal graph_def
      return graph_def
docs: Load GraphDef from a binary proto file.