I use a deque to fill a queue from the right, items get consumed from the left. Sometimes feedback from an external control mechanism will request an item be added to the queue with high priority. This item is then added to the left of the queue and will get consumed next, before all the others already in the queue. For me this was a good use case for a deque and it works well.

Same, but I also almost never use a stack or a priority queue. A list works like a stack if I ever need it (haven't yet), and if I'm reaching for a priority queue, I likely want something more complex like an actual scheduler or something (e.g. a timeout with a priority).

But I have at least used those once or twice. I've never used a deque as a deque, only as a queue.

If you want a first in first out it's better than a list. Deque is also whats powering thread safe queues in python where you want said FIFO functionality when sending from one thread to another. (typically the order doesn't matter since it's threads, but generally speaking it makes more sense to take the first thing going in, out of it too.)