def close(self):
		'''关闭与数据库的连接'''
		if VERBOSE:
			print 'Database connection CLOSE.'
		self.conn.close()
def _assert_type(self, value, t, id, expected):
        if not isinstance(value, t):
            raise TransactionError(_('Unexpected type of "{id}", {exp} expected.').format(id=id, exp=expected))