python双向队列deque实践与总结

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背景

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接收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

deque demo

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

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