code: def __getitem__(self, idx):
      return self.shapes[idx]
  
imports: import bisect
  from unittest import TestCase
  from unittest.mock import patch
  import numpy
  from torch.utils.data import ConcatDataset, Dataset
  from mmdet.datasets.samplers import GroupMultiSourceSampler, MultiSourceSampler
label_desc: Use image node_id 3 for calling the DummyDataset obj's underlying member method code with example usage: obj.__getitem__(idx) and returns: self