docs: def _phrase_doc_stream(paths, n, tokenizer=word_tokenize):
      """
      Generator to feed sentences to the phrase model.
      """
      i = 0
      p = Progress()
      for path in paths:
          with open(path, 'r') as f:
              for line in f:
                  i += 1
                  p.print_progress(i/n)
                  for sent in sent_tokenize(line.lower()):
                      tokens = tokenizer(sent)
                      yield tokens