docs: def preprocess(string):
      """
      Preprocess string to transform all diacritics and remove other special characters than appropriate
      
      :param string:
      :return:
      """
      string = unicode(string, encoding="utf-8")
      # convert diacritics to simpler forms
      string = regex1.sub(lambda x: accents[x.group()], string)
      # remove all rest of the unwanted characters
      return regex2.sub('', string).encode('utf-8')