code: def do_checkpoint(prefix, means, stds):
      def _callback(iter_no, sym, arg, aux):
          if "bbox_pred_weight" in arg:
              arg["bbox_pred_weight_test"] = (
                  arg["bbox_pred_weight"].T * mx.nd.array(stds)
              ).T
              arg["bbox_pred_bias_test"] = arg[
                  "bbox_pred_bias"
              ] * mx.nd.array(stds) + mx.nd.array(means)
          mx.model.save_checkpoint(prefix, iter_no + 1, sym, arg, aux)
          if "bbox_pred_weight" in arg:
              arg.pop("bbox_pred_weight_test")
              arg.pop("bbox_pred_bias_test")
  
      return _callback
  
label_desc: Use image node_id 1 for calling a global function with example usage: do_checkpoint(prefix, means, stds) and returns: _callback