code: def __len__(self):
      return 100
  
imports: import os
  import pickle
  import warnings
  from unittest.mock import patch
  import numpy
  import pytest
  from torch.utils.data import Dataset
  from baal.active import ActiveLearningDataset, heuristics
  from baal.active.active_loop import ActiveLearningLoop
label_desc: Use image node_id 2 for calling the MyDataset obj's underlying member method code with example usage: obj.__len__() and returns: int