code: def training_step(self, batch, batch_idx):
      x, y = batch
      return F.cross_entropy(self(x), y)
  
file_path: pytorch-lightning/examples/pytorch/hpu/mnist_sample.py
imports: import torch
  from jsonargparse import lazy_instance
  from lightning.pytorch import LightningModule
  from lightning.pytorch.cli import LightningCLI
  from lightning.pytorch.demos.mnist_datamodule import MNISTDataModule
  from lightning_habana import HPUPrecisionPlugin
  from torch.nn import functional
label_desc: Use image node_id 3 for calling the LitClassifier obj's underlying member method code with example usage: obj.training_step(batch, batch_idx) and returns: F