code: def _extract_trainable_values(self):
      if len(self._input_list) == 5:
          if isinstance(self._input_list[1].zvalue, autograd.Parameter):
              return [
                  self._input_list[1].zvalue.get_weight(),
                  self._input_list[2].zvalue.get_weight(),
              ]
          else:
              return [
                  self._input_list[1].zvalue,
                  self._input_list[2].zvalue,
              ]
      else:
          return None
  
file_path: analytics-zoo/pyzoo/zoo/pipeline/api/onnx/mapper/batchnormalization.py
imports: from zoo.pipeline.api.onnx.mapper.operator_mapper import OperatorMapper
  from zoo.pipeline.api.onnx.onnx_helper import OnnxHelper
  import zoo.pipeline.api.keras.layers
  import zoo.pipeline.api.autograd
  import numpy
label_desc: Use image node_id 3 for calling the BatchNormalizationMapper obj's underlying member method code with example usage: obj._extract_trainable_values() and returns: None, list, list