def GetFormatStringAttributeNames(self):
    """Retrieves the attribute names in the format string.

    Returns:
      set(str): attribute names.
    """
    if self._format_string_attribute_names is None:
      self._format_string_attribute_names = []
      for format_string_piece in self.FORMAT_STRING_PIECES:
        attribute_names = self._FORMAT_STRING_ATTRIBUTE_NAME_RE.findall(
            format_string_piece)

        if attribute_names:
          self._format_string_attribute_names.extend(attribute_names)

    return set(self._format_string_attribute_names)
Retrieves the attribute names in the format string.

    Returns:
      set(str): attribute names.