docstr: :return: list of OnnxInput
docstr_tok: [":","return",":","list","of","OnnxInput"]
code: def _extract_model_inputs(self):
      """
      :return: list of OnnxInput
      """
      input = OnnxInput(
          name=self.op_name,
          zvalue=OnnxHelper.to_numpy(self.onnx_attr["value"]),
      )
      return [self._to_zoo_input(input, is_constant=True)]
  
file_path: analytics-zoo/pyzoo/zoo/pipeline/api/onnx/mapper/constant.py
imports: import bigdl.nn.layer
  import numpy
  import zoo.pipeline.api.keras.layers
  from zoo.pipeline.api.onnx.mapper.operator_mapper import OperatorMapper
  from zoo.pipeline.api.onnx.onnx_helper import OnnxHelper
  from zoo.pipeline.api.onnx.onnx_loader import OnnxInput
label_desc: Use image node_id 2 for calling the ConstantMapper obj's underlying member method code with example usage: obj._extract_model_inputs() and returns: list