code: def _loss_step(self, batch):
      return self._base_step(batch=batch, mode="loss")
  
imports: import logging
  from typing import Callable, Optional, Union
  import lightning.pytorch
  import torchmetrics
  from lightning.pytorch.utilities import grad_norm
  from torch.nn.modules.loss import _Loss
  from torchmetrics.aggregation import BaseAggregator
  from ..constants import BBOX, IMAGE, LABEL
  from .utils import apply_layerwise_lr_decay, apply_single_lr, apply_two_stages_lr, get_lr_scheduler, get_optimizer, remove_parameters_without_grad
label_desc: Use image node_id 4 for calling the MMDetLitModule obj's underlying member method code with example usage: obj._loss_step(batch) and returns: self