code: def _generate_phrases(self, sentences):
          
          phrase_list = set()
          # Create contender phrases from sentences.
          for sentence in sentences:
              word_list = [word.lower() for word in wordpunct_tokenize(sentence)]
              phrase_list.update(self._get_phrase_list_from_words(word_list))
          return phrase_list
docs: Method to generate contender phrases given the sentences of the text
          document.
  
          :param sentences: List of strings where each string represents a
                            sentence which forms the text.
          :return: Set of string tuples where each tuple is a collection
                   of words forming a contender phrase.