code: def add_token(tokens_a, tokens_b=None):
      assert len(tokens_a) >= 1
  
      tokens = []
      segment_ids = []
  
      tokens.append("[CLS]")
      segment_ids.append(0)
  
      for token in tokens_a:
          tokens.append(token)
          segment_ids.append(0)
  
      tokens.append("[SEP]")
      segment_ids.append(0)
  
      if tokens_b != None:
          assert len(tokens_b) >= 1
  
          for token in tokens_b:
              tokens.append(token)
              segment_ids.append(1)
  
          tokens.append("[SEP]")
          segment_ids.append(1)
  
      return tokens, segment_ids
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import collections
  import unicodedata
  import six
label_desc: Use image node_id 19 for calling a global function with example usage: add_token(tokens_a, tokens_b) and returns: tokens,  segment_ids