code: def __clean_and_tokenize(self, doc_list):
          doc_list = filter(
              lambda x: x is not None and len(x) <= GitSuggest.MAX_DESC_LEN,
              doc_list,
          )
          cleaned_doc_list = list()
          tokenizer = RegexpTokenizer(r"[a-zA-Z]+")
          stopwords = self.__get_words_to_ignore()
          dict_words = self.__get_words_to_consider()
          for doc in doc_list:
              lower = doc.lower()
              tokens = tokenizer.tokenize(lower)
              tokens = [tok for tok in tokens if tok in dict_words]
              tokens = [tok for tok in tokens if tok not in stopwords]
              tokens = [tok for tok in tokens if tok is not None]
              cleaned_doc_list.append(tokens)
          return cleaned_doc_list