class_docstr: Vocabulary extracts set of unique tokens and
  constructs token to index and index to token lookup tables.
class_docstr_tok: ["Vocabulary","extracts","set","of","unique","tokens","and","constructs","token","to","index","and","index","to","token","lookup","tables","."]
code: def __getitem__(self, tokens):
      if not isinstance(tokens, (list, tuple)):
          return self.token_to_idx.get(tokens, self.unk)
      return [self.__getitem__(token) for token in tokens]
  
imports: import collections
  import random
  import re
  import jax
  import jax.numpy
  import tensorflow_datasets
  import objax
  from objax.functional import one_hot
  from objax.zoo.rnn import RNN
label_desc: Use image node_id 3 for calling the Vocabulary obj's underlying member method code with example usage: obj.__getitem__(tokens) and returns: unknown, self