code: def __getitem__(self, item):
      return self.data[item]
  
imports: import numpy
  import pytest
  from functools import partial
  from itertools import chain
  from copy import deepcopy
  from fastNLP.core.samplers.reproducible_sampler import RandomSampler, SortedSampler, SequentialSampler
  from tests.helpers.datasets.torch_data import TorchNormalDataset
label_desc: Use image node_id 2 for calling the DatasetWithVaryLength obj's underlying member method code with example usage: obj.__getitem__(item) and returns: self