code: def unk_idx(self):
      return self.w2i["<unk>"]
  
imports: import io
  import json
  import os
  import pickle
  from collections import Counter, OrderedDict
  from collections import defaultdict
  import numpy
  import torch
  import torch.nn
  from nltk.tokenize import sent_tokenize, word_tokenize
  from torch.utils.data import Dataset
  from torchvision import transforms, models, datasets
label_desc: Use image node_id 7 for calling the CUBSentences obj's underlying member method code with example usage: obj.unk_idx() and returns: self