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.

def sanitize_words(self, words):
    """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.
    """
    _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