I agree that popping old inputs is the normal way. What I'm trying to say is that it doesn't feel like "old" or "inputs" when you multiply. In that case (and maybe this is just me), it feels like a "reasonable" outcome could be to get an outcome similar to multiplying a list and then slicing the result to maxlen. I don't think it *should* do that, but either behavior feels weird, solely because sequence multiplication has never been applied to a bounded sequence before (to my knowledge), so the expectations aren't set.

You end up with weird behaviors like len(seq) * 3 != len(seq * 3), which is a normal and expected outcome with every other sequence. If you know you're dealing with a bounded deque, it's less unexpected, but this is trying to make a deque a drop-in replacement for any other sequence when it doesn't behave like one.