code: def _replace_oov(original_vocab, line):
      """Replace out-of-vocab words with "UNK".
  
      This maintains compatibility with published results.
  
      Args:
        original_vocab: a set of strings (The standard vocabulary for the dataset)
        line: a unicode string - a space-delimited sequence of words.
  
      Returns:
        a unicode string - a space-delimited sequence of words.
      """
      return " ".join(
          [
              word if word in original_vocab else "UNK"
              for word in line.split()
          ]
      )
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import os
  import tarfile
  from six.moves import range
  from tensor2tensor.data_generators import generator_utils
  from tensor2tensor.data_generators import problem
  from tensor2tensor.data_generators import text_encoder
  from tensor2tensor.data_generators import text_problems
  from tensor2tensor.utils import registry
  import tensorflow.compat.v1
label_desc: Use image node_id 2 for calling a global function with example usage: _replace_oov(original_vocab, line) and returns: str