popleft && appenleft :) note

[popexizhi:
py2,py3都支持啊，mark deque竟然可以popleft 和 appendleft
]

>>> from collections import deque
>>> q = deque(maxlen=3)
>>> q = deque()
>>> q.append(1)
>>> q.append(2)
>>> q.append(3)
>>> q
deque([1, 2, 3])
>>> q.appendleft(3)
>>> q
deque([3, 1, 2, 3])
>>> q.pop()
3
>>> q
deque([3, 1, 2])
>>> q.popleft()
3

>>> q
deque([1, 2])