code: def set_lengths(self):
      self._total_length = 0
      for loader in self.loaders.values():
          # Some loaders might not have dataset attribute
          # set, in this case we won't consider them in
          # dataset lengths.
          if not hasattr(loader, "dataset"):
              continue
  
          dataset_instance = loader.dataset
  
          if hasattr(dataset_instance, "__len__"):
              dataset_instance_length = len(dataset_instance)
              assert (
                  dataset_instance_length
              ), f"dataset: {self.dataset_type} is empty"
              self._total_length += dataset_instance_length
  
imports: import logging
  import warnings
  from typing import Dict, Iterator
  import torch
  from mmf.common.sample import convert_batch_to_sample_list, SampleList
  from mmf.datasets import iteration_strategies
  from mmf.utils.build import build_dataloader_and_sampler, build_dataset
  from mmf.utils.dataset import dataset_list_from_config
  from mmf.utils.distributed import broadcast_scalar, get_world_size, is_dist_initialized, is_main, is_xla
  from mmf.utils.general import get_batch_size, get_current_device
  from omegaconf import OmegaConf
  from torch.utils.data.dataloader import DataLoader, Sampler
label_desc: Use image node_id 2 for calling the MultiDataLoader obj's underlying member method code with example usage: obj.set_lengths() without return types