code: def export_graph_def(self):
      return self._refine_graph.export_graph_def()
  
file_path: nnabla/python/src/nnabla/utils/converter/tensorflow/common.py
imports: import collections
  from .refine_graph import RefineGraph
  from .refine_parser import RefineParser
label_desc: Use image node_id 3 for calling the OptimizePb obj's underlying member method code with example usage: obj.export_graph_def() and returns: self