code: def execute(self):
      self._refine_graph = RefineGraph(self._graph_def)
      self._refine_parser = RefineParser(self._refine_graph)
      self._refine_graph.prepare()
      self._refine_parser.parse()
      return self
  
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 2 for calling the OptimizePb obj's underlying member method code with example usage: obj.execute() and returns: self