code: def set_model_doc_string(model, doc, override=False):
      
      if model is None or not isinstance(model, onnx_proto.ModelProto):
          raise ValueError("Model is not a valid ONNX model.")
      if not convert_utils.is_string_type(doc):
          raise ValueError("Doc must be a string type.")
      if model.doc_string and not doc and override is False:
          raise ValueError("Failing to overwrite the doc string with a blank string, set override to True if intentional.")
      model.doc_string = doc
docs: Sets the doc string of the ONNX model.
  
      :param model: instance of an ONNX model
      :param doc: string containing the doc string that describes the model.
      :param override: bool if true will always override the doc string with the new value
  
      Example:
  
      ::
          from onnxmltools.utils import set_model_doc_string
          onnx_model = load_model("SqueezeNet.onnx")
          set_model_doc_string(onnx_model, "Sample doc string")