code: def _get_mapper_params(self):
      
      reader_params = self.input_reader_cls.params_to_json(
          self.input_reader_params)
      # TODO(user): Do the same for writer params.
      return {"input_reader": reader_params,
              "output_writer": self.output_writer_params}
docs: Converts self to model.MapperSpec.params.