code: def save_model(model, file_path):
      
      if model is None or not isinstance(model, onnx_proto.ModelProto):
          raise ValueError("Model is not a valid ONNX model.")
      directory = os.path.dirname(os.path.abspath(file_path))
      if not path.exists(directory):
          raise FileNotFoundError("Directory does not exist {0}".format(directory))
      with open(file_path, 'wb') as f:
          f.write(model.SerializeToString())
docs: Saves an ONNX model to a ProtoBuf object.
      :param model: ONNX model
      :param file_path: ONNX file (full file name)
  
      Example:
  
      ::
  
          from onnxmltools.utils import save_model
          save_model(onnx_model, 'c:/test_model.onnx')