python deque

双端队列（deque）具有从任一端添加和删除元素的功能。deque模块是集合库的一部分。它具有添加和删除可以直接用参数调用的元素的方法。在下面的程序中，我们导入集合模块并声明一个双端队列。不需要任何类，我们直接使用内置的实现这些方法。

import collections
# create a deque
doubleended = collections.deque(["mon","tue","wed"])
print (doubleended)

# append to the right
print("adding to the right: ")
doubleended.append("thu")
print (doubleended)

# append to the left
print("adding to the left: ")
doubleended.appendleft("sun")
print (doubleended)

# remove from the right
print("removing from the right: ")
doubleended.pop()
print (doubleended)

# remove from the left
print("removing from the left: ")
doubleended.popleft()
print (doubleended)

# reverse the dequeue
print("reversing the deque: ")
doubleended.reverse()
print (doubleended)

当上面的代码被执行时，它会产生以下结果：

deque(['mon', 'tue', 'wed'])
adding to the right:
deque(['mon', 'tue', 'wed', 'thu'])
adding to the left:
deque(['sun', 'mon', 'tue', 'wed', 'thu'])
removing from the right:
deque(['sun', 'mon', 'tue', 'wed'])
removing from the left:
deque(['mon', 'tue', 'wed'])
reversing the deque:
deque(['wed', 'tue', 'mon'])