code: def prepare_data(self):
      # download only
      self.dataset_cls(self.data_dir, train=True, download=True)
      self.dataset_cls(self.data_dir, train=False, download=True)
  
imports: import torch
  from lightning.pytorch.core.datamodule import LightningDataModule
  from lightning_utilities.core.imports import RequirementCache
  from torch.utils.data import DataLoader
  from tests_pytorch.helpers.datasets import MNIST, SklearnDataset, TrialMNIST
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