How to use the aiozk.iterables.drain function in aiozk

def drain_all_pending(self):
        for special_xid in protocol.SPECIAL_XIDS:
            for f in iterables.drain(self.pending_specials[special_xid]):
                yield f
        for _, f in iterables.drain(self.pending):
            yield f

def transition_to(self, state):
        if (self.current_state, state) not in self.valid_transitions:
            raise exc.InvalidStateTransition(
                "Invalid session state transition: %s -> %s" % (
                    self.current_state, state
                )
            )

        log.debug("Session transition: %s -> %s", self.current_state, state)

        self.current_state = state

        for future in drain(self.futures[state]):
            if not future.done():
                future.set_result(None)

def drain_all_pending(self):
        for special_xid in protocol.SPECIAL_XIDS:
            for f in iterables.drain(self.pending_specials[special_xid]):
                yield f
        for _, f in iterables.drain(self.pending):
            yield f