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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 async def close(self):
 """Close this SAConnection. This results in a release of the underlying database resources, that is, the underlying connection referenced internally. The underlying connection is typically restored back to the connection-holding Pool referenced by the Engine that produced this SAConnection. Any transactional state present on the underlying connection is also unconditionally released via calling Transaction.rollback() method. After .close() is called, the SAConnection is permanently in a closed state, and will allow no further operations. """

        if self._connection is None:
            return

        if self._transaction is not None:
            await self._transaction.rollback()
            self._transaction = None
        # don't close underlying connection, it can be reused by pool
        # conn.close()
        self._engine.release(self)
        self._connection = None
        self._engine = None