2.py

    def _get_next_words(self, word):
        if word not in self.next_words_dict:
            self._generate_next_words_list(word)

        return self.next_words_dict[word]

    def _generate_next_words_list(self, word):
        next_words = []
        word_array = list(word)
        for i in range(len(word_array)):
            old_c = word_array[i]
            for c in ascii_lowercase:
                if not c == old_c:
                    word_array[i] = c
                    new_word = ''.join(word_array)

                    if new_word not in self.word_levels and new_word in self.words_map:
                        next_words.append(new_word)

            word_array[i] = old_c

        self.next_words_dict[word] = next_words