docs: def _load_stopwords(file_path):
      '''
      load stop words
      '''
      global _stopwords
      if sys.version_info[0] < 3:
          words = open(file_path, 'r')
      else:
          words = open(file_path, 'r', encoding='utf-8')
      stopwords = words.readlines()
      for w in stopwords:
          _stopwords.add(any2unicode(w).strip())