You can think of a deque as a list with the functionality of insert and pop items from both front and back, and it can also do the rotation.
First, the deque can be treated as a list, the methods append(), extend(), and pop() work as usual.
d = deque()
d.append(1)
# deque([1])
d.extend([2, 3])
# deque([1, 2, 3])
d.pop() # 3
# deque([1, 2])But, here comes the skills that only deque has, the methods appendleft(), extendleft(), and popleft() can insert and pop the elements from the beginning of the deque.
Be careful that the method
extendleft()will reverse the order of input
d = deque()
d.extendleft([1, 2])
# deque([2, 1])
d.appendleft(3)
# deque([3, 2, 1])
d.popleft() # 3
# deque([2, 1])deque also has a method rotate() to rotate itself. If you call it with a positive integer, it will perform a right rotation; if you call it with a negative integer, it will perform a left rotation.
d = deque([1, 2, 3, 4])
d.rotate(1)
# deque([4, 1, 2, 3])
d.rotate(-2)
# deque([2, 3, 4, 1])This is a deque example from Python documentation, it uses the deque to maintain a list of elements by appending to the right and popping to the left.
def moving_average(iterable, n=3):
# moving_average([40, 30, 50, 46, 39, 44]) --> 40.0 42.0 45.0 43.0
# http://en.wikipedia.org/wiki/Moving_average
it = iter(iterable)
d = deque(itertools.islice(it, n-1))
d.appendleft(0)
s = sum(d)
for elem in it:
s += elem - d.popleft()
d.append(elem)
yield s / n| Article | Link |
|---|---|
| collections - deque | https://docs.python.org/3/library/collections.html#collections.deque |
| Python deque用法介绍 | https://blog.csdn.net/liangguohuan/article/details/7088265 |
| The Complete Python Course For Beginners | https://youtu.be/sxTmJE4k0ho?list=LL&t=16357 |