def get_last_tid(self):
        try:
            spec = {'tid': {'$gt': 0}}
            sort = [('tid', -1)]
            row = self.db.docs.find_one(spec, sort=sort)
        except Exception as e:
            raise DatabaseException(e)
        if row:
            return row['tid']
        return 0
def test_vice_versa(self):
        class First(Structure):
            pass
        class Second(Structure):
            pass

        First._fields_ = [("second", Second)]

        try:
            Second._fields_ = [("first", First)]
        except AttributeError as details:
            self.assertTrue("_fields_ is final" in
                            str(details))
        else:
            self.fail("AttributeError not raised")