1. 特殊的佇列collections.deque，儲存最後N個元素

儲存有限的歷史記錄可算是collections.deque的完美應用場景了。

deque與list的區別是：

deque不僅僅支援append、pop實現後進先出，還支援appendleft、popleft對任何一邊元素進行操作;

>>> from collections import deque

>>> q = deque(maxlen=3)
>>> q.append(1)
>>> q.append(2)
>>> q.append(3)
>>> q.append(4)
>>> q
deque([2, 3, 4], maxlen=3)
>>> q.pop()
4
>>> q
deque([2, 3], maxlen=3)
>>> q.appendleft(1)
>>> q
deque([1, 2, 3], maxlen=3)
 

2. heapq 模組的函式應用於佇列（找到最大或者最小的N個元素）

我們想在某個集合中找出最大或者最小的N個元素，可以採用heapq模組中，有兩個函式------nlargest() 和nsmallest()

>>> nums = [1, 8, 2, 23, 7, -4, 18, 23, 42, 37, 2]
>>> import heapq
>>> print(heapq.nlargest(3, nums))
[42, 37, 23]
 

import heapq
protfolio=[
{'name':'IBM','shares':100,'price':91.1},
{'name':'FB','shares':200,'price':21.09},
{'name':'AAPL','shares':50,'price':543.22},
{'name':'HPQ','shares':35,'price':31.75},
{'name':'YHOO','shares':45,'price':16.35},
{'name':'ACME','shares':75,'price':115.65}

    ]
cheap=heapq.nsmallest(3,protfolio,key=lambda s:s['price'])
print(cheap)
expensive=heapq.nlargest(3,protfolio,key=lambda s:s['price'])
print(expensive)
 

特別指出，nlargest() 和nsmallest()支援第三個引數key=callable，這個key和sorted,max,min用法一樣