code: def GetFormatStringAttributeNames(self):
      
      if self._format_string_attribute_names is None:
        self._format_string_attribute_names = (
            self._FORMAT_STRING_ATTRIBUTE_NAME_RE.findall(
                self.FORMAT_STRING))
  
      return set(self._format_string_attribute_names)
docs: Retrieves the attribute names in the format string.
  
      Returns:
        set(str): attribute names.