class_docstr: Simple vocabulary wrapper.
class_docstr_tok: ["Simple","vocabulary","wrapper","."]
code: def __call__(self, word):
      if not word in self.word2idx:
          return self.word2idx["<unk>"]
      return self.word2idx[word]
  
file_path: pytorch-tutorial/tutorials/03-advanced/image_captioning/build_vocab.py
imports: import nltk
  import pickle
  import argparse
  from collections import Counter
  from pycocotools.coco import COCO
label_desc: Use image node_id 3 for calling the Vocabulary obj's underlying member method code with example usage: obj.__call__(word) and returns: self, self