code: def export_to_file(self, output_file):
      self._refine_graph.save_back(output_file)
  
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 4 for calling the OptimizePb obj's underlying member method code with example usage: obj.export_to_file(output_file) without return types