def _on_auth(self, user):
        """
        """
        if not user:
            self.abort(403)

        # try user name, fallback to uid.
        username = user.pop('username', None)
        if not username:
            username = user.pop('uid', '')

        auth_id = username % 'facebook|%s'
        self.auth.login_with_auth_id(auth_id, remember=True,
            session_key=user.get('session_key'))
        return self._on_auth_redirect()
dataset/ETHPy150Open moraes/tipfy/examples/auth/app/handlers.py/FacebookAuthHandler._on_auth/swapped operands of `%`