code: def start_bundle(self, element=None):
      
      import tensorflow as tf
      from trainer import feature_transforms
  
      g = tf.Graph()
      session = tf.Session(graph=g)
  
      # Build the transformation graph
      with g.as_default():
        transformed_features, _, placeholders = (
            feature_transforms.build_csv_serving_tensors_for_transform_step(
                analysis_path=self._analysis_output_dir, 
                features=self._features, 
                schema=self._schema,
                stats=self._stats,
                keep_target=True))
        session.run(tf.tables_initializer())
      
      self._session = session
      self._transformed_features = transformed_features
      self._input_placeholder_tensor = placeholders['csv_example']
docs: Build the transfromation graph once.