old_contents: # Natural Language Toolkit: Language Model Unit Tests
  #
  # Copyright (C) 2001-2020 NLTK Project
  # Author: Ilia Kurenkov <ilia.kurenkov@gmail.com>
  # URL: <http://nltk.org/>
  # For license information, see LICENSE.TXT
  import unittest
  
  from nltk.lm.preprocessing import padded_everygram_pipeline
  
  
  class TestPreprocessing(unittest.TestCase):
      def test_padded_everygram_pipeline(self):
          expected_train = [
              [
                   ('<s>',),
                   ('<s>', 'a'),
                   ('a',),
                   ('a', 'b'),
                   ('b',),
                   ('b', 'c'),
                   ('c',),
                   ('c', '</s>'),
                   ('</s>',)
               ]
          ]
          expected_vocab = ["<s>", "a", "b", "c", "</s>"]
          train_data, vocab_data = padded_everygram_pipeline(2, [["a", "b", "c"]])
          self.assertEqual([list(sent) for sent in train_data], expected_train)
          self.assertEqual(list(vocab_data), expected_vocab)
  
new_contents: # Natural Language Toolkit: Language Model Unit Tests
  #
  # Copyright (C) 2001-2020 NLTK Project
  # Author: Ilia Kurenkov <ilia.kurenkov@gmail.com>
  # URL: <http://nltk.org/>
  # For license information, see LICENSE.TXT
  import unittest
  
  from nltk.lm.preprocessing import padded_everygram_pipeline
  
  
  class TestPreprocessing(unittest.TestCase):
      def test_padded_everygram_pipeline(self):
          expected_train = [
              [
                   ("<s>",),
                   ("<s>", "a"),
                   ("a",),
                   ("a", "b"),
                   ("b",),
                   ("b", "c"),
                   ("c",),
                   ("c", "</s>"),
                   ("</s>",)
               ]
          ]
          expected_vocab = ["<s>", "a", "b", "c", "</s>"]
          train_data, vocab_data = padded_everygram_pipeline(2, [["a", "b", "c"]])
          self.assertEqual([list(sent) for sent in train_data], expected_train)
          self.assertEqual(list(vocab_data), expected_vocab)
  
subject: Revert to double quotes.