<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def item(self, index: int) -> Optional[Attr]: """Return ``index``-th attr node."""

        if 0 <= index < len(self):
            return self._dict[tuple(self._dict.keys())[index]]
        return None