Schedule an event to be emitted at a certain time.

        :param when: an absolute timestamp
        :param data_tuple: a 2-tuple (flavor, data)
        :return: an event object, useful for cancelling.

def event_at(self, when, data_tuple):
        """
        Schedule an event to be emitted at a certain time.

        :param when: an absolute timestamp
        :param data_tuple: a 2-tuple (flavor, data)
        :return: an event object, useful for cancelling.
        """
        return self._base.event_at(when, self.make_event_data(*data_tuple))