code: def __len__(self):
      return 100
  
imports: import pickle
  import unittest
  import unittest.mock
  import warnings
  import datasets
  import numpy
  import pytest
  import torch.utils.data
  from torchvision.transforms import Lambda
  from baal.active import ActiveLearningDataset
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