Now Argument Clinic generates more efficient (but more cumbersome) code, so there may be new reasons of using it. Please test the performance of the deque constructor (deque(), deque(()), deque((), 10), deque((), maxlen=10)), methods index() and rotate(), builtins iter() and reversed(). It is hard to test insert() because it mutates the deque and I do not expect anything beside noise for other methods.