code: def get_pad_index(self):
      return self.PAD_INDEX
  
imports: import logging
  import os
  from collections import defaultdict
  import numpy
  import torch
  from mmf.utils.configuration import get_mmf_cache_dir
  from mmf.utils.distributed import is_main, synchronize
  from mmf.utils.file_io import PathManager
  from mmf.utils.general import get_absolute_path
  from torchtext import vocab
label_desc: Use image node_id 5 for calling the BaseVocab obj's underlying member method code with example usage: obj.get_pad_index() and returns: self