code: def _transform(self, example):
      time.sleep(0.05 + random.random() * 0.1)
      return example
  
imports: import time
  import unittest
  import json
  import os
  import random
  from pgl.utils.data.dataset import Dataset, StreamDataset
  from pgl.utils.data.dataloader import Dataloader
label_desc: Use image node_id 4 for calling the ListDataset obj's underlying member method code with example usage: obj._transform(example) and returns: example