code: def __len__(self):
      return self.len
  
imports: import math
  from typing import Union
  import pytest
  import torch
  import pytorch_lightning
  from pytorch_lightning import LightningModule, Trainer
  from pytorch_lightning.trainer.states import RunningStage
  from torch.utils.data import DataLoader, Dataset
label_desc: Use image node_id 3 for calling the RandomDataset obj's underlying member method code with example usage: obj.__len__() and returns: self