code: def prepare_data(self):
      # download
      MNIST(self.data_dir, train=True, download=True)
      MNIST(self.data_dir, train=False, download=True)
  
imports: import math
  import os
  import torch
  from filelock import FileLock
  import pytorch_lightning
  from torch.nn import functional
  from torch.utils.data import DataLoader, random_split
  from torchmetrics import Accuracy
  from torchvision import transforms
  from torchvision.datasets import MNIST
  from ray.tune.integration.pytorch_lightning import TuneReportCheckpointCallback
  from ray import train, tune
label_desc: Use image node_id 2 for calling the MNISTDataModule obj's underlying member method code with example usage: obj.prepare_data() without return types