code: def try_fast_read(self):
      # Don't fast read in case of test set.
      if self._dataset_type == "test":
          return
  
      if (
          hasattr(self, "_should_fast_read")
          and self._should_fast_read is True
      ):
          logger.info(
              f"Starting to fast read {self.dataset_name} {self.dataset_type} "
              + "dataset"
          )
          self.cache = {}
          for idx in tqdm.tqdm(
              range(len(self.annotation_db)),
              miniters=100,
              disable=not is_main(),
          ):
              self.cache[idx] = self.load_item(idx)
  
file_path: mmf/mmf/datasets/builders/vqa2/dataset.py
imports: import logging
  import torch
  import tqdm
  from mmf.common.sample import Sample
  from mmf.datasets.mmf_dataset import MMFDataset
  from mmf.utils.distributed import is_main
label_desc: Use image node_id 3 for calling the VQA2Dataset obj's underlying member method code with example usage: obj.try_fast_read() without return types