code: def get_special_vocab(vocabulary_size):
      """Returns the `SpecialVocab` instance for a given vocabulary size."""
      return SpecialVocab(*range(vocabulary_size, vocabulary_size + 3))
  
file_path: seq2seq/seq2seq/data/vocab.py
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import collections
  import tensorflow
  from tensorflow import gfile
label_desc: Use image node_id 2 for calling a global function with example usage: get_special_vocab(vocabulary_size) and returns: SpecialVocab