code: def _ReformatMessageString(self, message_string):
      
      def _PlaceHolderSpecifierReplacer(match_object):
        """Replaces message string place holders into Python format() style."""
        expanded_groups = []
        for group in match_object.groups():
          try:
            place_holder_number = int(group, 10) - 1
            expanded_group = '{{{0:d}:s}}'.format(place_holder_number)
          except ValueError:
            expanded_group = group
  
          expanded_groups.append(expanded_group)
  
        return ''.join(expanded_groups)
  
      if not message_string:
        return None
  
      message_string = self._WHITE_SPACE_SPECIFIER_RE.sub(r'', message_string)
      message_string = self._TEXT_SPECIFIER_RE.sub(r'\\\1', message_string)
      message_string = self._CURLY_BRACKETS.sub(r'\1\1', message_string)
      return self._PLACE_HOLDER_SPECIFIER_RE.sub(
          _PlaceHolderSpecifierReplacer, message_string)
docs: Reformats the message string.
  
      Args:
        message_string (str): message string.
  
      Returns:
        str: message string in Python format() (PEP 3101) style.