code: def __len__(self) -> int:
      return self._open_iterator().total_size
  
file_path: mmf/mmf/datasets/builders/airstore/dataset.py
imports: import logging
  from io import BytesIO
  from typing import Any, Iterable
  import torch
  from iopath.common.file_io import PathManager
  from mmf.common.sample import Sample
  from mmf.datasets.base_dataset import BaseDataset
  from mmf.utils.general import get_batch_size
  from PIL import Image, ImageFile
label_desc: Use image node_id 4 for calling the AirstoreDataset obj's underlying member method code with example usage: obj.__len__() and returns: self