Why does python use both reference counting and mark-and-sweep for gc?

Question

My question is why does python use both reference counting and mark-and-sweep for gc? Why not only mark-and-sweep?

My initial guess is that using reference counting

Answer 1

Reference counting deallocates objects sooner than garbage collection.

But as reference counting can't handle reference cycles between unreachable objects, Python uses a garbage collector (really just a cycle collector) to collect those cycles when they exist.