1.什么是双端队列
deque的英文意思是Double-Ended Queue，deque是为了在两端高效实现插入和删除操作的双向列表，适合用于队列和栈：deque除了实现list的append()和pop()外，还支持appendleft()和popleft()，这样就可以非常高效地往头部或者尾部添加或删除元素
基本概念与常见的list使用区别如下所示
常用的接口
deque：append和popleft
Deque基本表现- 优点
（1）deque受GIL管理，线程安全。list没有GIL锁，所以线程不安全。也就是说，在并发场景中，list可能会导致一致性问题，而deque不会。
（2）deque支持固定长度。当长度满了，当我们继续使用append时，它会自动弹出最早插入的数据。
（3） deque 更快
See the following code example of Deque in Python.
#importing deque from collections module
from collections import deque
#initializing the deque object
deq = deque(['apple', 'mango', 'orange'])
#printing the initial deque object
print("Printing the initial deque object items n" , deq, 'n')
#append(x) demonstration
print("Appending a new element to the right of deque")
deq.append('papaya')
print(deq , 'n')
#appendleft(x) demonstration
print("Appending a new element to the left of deque")
deq.appendleft('strawberry')
print(deq , 'n')
#count(x) demonstration
print("Counting the the occurrence of apple in deque")
print(deq.count('apple') , 'n')
#extend(iterable) demonstration
deq.extend(['grapes', 'watermelon'])
print("Extending the deque with new items on the right")
print(deq, "n")
extendleft(iterable) demonstration
deq.extendleft(['pear', 'guava'])
print("Extending the deque with new items on the left")
print(deq, "n")
#index(x [, start [, stop]]) demonstration
print("Finding the index of an item")
print(deq.index('strawberry'), "n")
#insert(i,x) demonstration
print("Inserting an item to the deque by specifiying the index")
deq.insert(2,'banana')
print(deq, "n")
#pop() demonstration
print("Popping out last item from the right")
print(deq.pop(), "n")
#popleft() demonstration
print("Popping out first item from the left")
print(deq.popleft(), "n")
#remove() demonstration
print("Removing an item from the deque")
deq.remove("apple")
print(deq, "n")
运行结果：
Printing the initial deque object items deque(['apple', 'mango', 'orange']) Appending a new element to the right of deque deque(['apple', 'mango', 'orange', 'papaya']) Appending a new element to the left of deque deque(['strawberry', 'apple', 'mango', 'orange', 'papaya']) Counting the the occurrence of apple in deque 1 Extending the deque with new items on the right deque(['strawberry', 'apple', 'mango', 'orange', 'papaya', 'grapes', 'watermelon']) Extending the deque with new items on the left deque(['guava', 'pear', 'strawberry', 'apple', 'mango', 'orange', 'papaya', 'grapes', 'watermelon']) Finding the index of an item 2 Inserting an item to the deque by specifiying the index deque(['guava', 'pear', 'banana', 'strawberry', 'apple', 'mango', 'orange', 'papaya', 'grapes', 'watermelon']) Popping out last item from the right watermelon Popping out first item from the left guava Removing an item from the deque deque(['pear', 'banana', 'strawberry', 'mango', 'orange', 'papaya', 'grapes'])总结
如果需要使用一个容器来处理数据 请使用deque
