docs: def convert(self, string, preprocess = None):
          """
          Swap characters from a script to transliteration and vice versa. 
          Optionally sanitize string by using preprocess function.
  
          :param preprocess:
          :param string:
          :return:
          """
          string = unicode(preprocess(string) if preprocess else string, encoding="utf-8")
          if self.regex:
              return self.regex.sub(lambda x: self.substitutes[x.group()], string).encode('utf-8')
          else:
              return string