def _cbAnonymousAuthentication(self, result):
        """
        Save the state resulting from a successful anonymous cred login.
        """
        (iface, avatar, logout) = result
        if issubclass(iface, IMessageDeliveryFactory):
            self.deliveryFactory = avatar
            self.delivery = None
        elif issubclass(iface, IMessageDelivery):
            self.deliveryFactory = None
            self.delivery = avatar
        else:
            raise RuntimeError("%s is not a supported interface" % (iface.__name__,))
        self._onLogout = logout
        self.challenger = None

        Save the state resulting from a successful anonymous cred login.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/mail/smtp.py