from collections import Counter, deque q = deque() q.append(1) q.append(2) q.appendleft(3) q.append(4) assert len(q) == 4 assert q == deque([3, 1, 2, 4]) assert q.popleft() == 3 assert q.pop() == 4 assert len(q) == 2 assert q == deque([1, 2])