Assigning different Exception message

[Tor Erik Soenvisen]

        try:
            self.cursor.execute(sql)
        except AttributeError, e:
            if e.message == "oracleDB instance has no attribute 'cursor'":
                e.message = 'oracleDB.open() must be called before' + \
                            ' oracleDB.query()'
            raise AttributeError, e

This code does not re-assign e's message when the conditional is satisfied. 
Why not?

regards