code: def step(self, batch):
      self._assert_autocast_enabled()
      output = self(batch)
      is_bfloat16 = (
          self.trainer.precision_plugin.precision == "bf16-mixed"
      )
      assert (
          output.dtype == torch.float16
          if not is_bfloat16
          else torch.bfloat16
      )
      return self.loss(output)
  
file_path: pytorch-lightning/tests/tests_pytorch/models/test_amp.py
imports: import os
  from unittest import mock
  import pytest
  import torch
  from lightning.fabric.plugins.environments import SLURMEnvironment
  from lightning.pytorch import Trainer
  from lightning.pytorch.demos.boring_classes import BoringModel, RandomDataset
  from torch.utils.data import DataLoader
  import tests_pytorch.helpers.utils
  from tests_pytorch.helpers.runif import RunIf
label_desc: Use image node_id 1 for calling the AMPTestModel obj's underlying member method code with example usage: obj.step(batch) and returns: self