code: def __getitem__(self, idx):
      query_and_psgs = self.idx2psgs[idx]
      query_id, psg_ids = query_and_psgs[0], query_and_psgs[1:]
      inputs = self._preprocess_fn(query_id, psg_ids)
      return [*inputs, query_id, np.array(psg_ids)]
  
imports: import multiprocessing
  import os
  import pickle
  import random
  from typing import Optional
  import numpy
  from torch.utils.data import Dataset
  from nemo.collections.common.tokenizers.tokenizer_spec import TokenizerSpec
label_desc: Use image node_id 2 for calling the BertInformationRetrievalDataset obj's underlying member method code with example usage: obj.__getitem__(idx) and returns: list