code: def sanitize_words(self, words):
      
      _words = []
      for w in words:
        if isinstance(w, string_types) and not isinstance(w, unicode):
          _words.append(unicode(w, encoding="utf-8"))
        else:
          _words.append(w)
      return _words
docs: Guarantees that all textual symbols are unicode.
  
      Note:
        We do not convert numbers, only strings to unicode.
        We assume that the strings are encoded in utf-8.