Queues in Python

The deque object we discussed about before can be also used to represent a normal Queue.

The usual enqueuing and dequeuing can be done by using the methods append and popleft, respectively.

>>> from collections import deque

>>> q = deque()

>>> q.append(1)
>>> q.append(2)
>>> q.append(3)
>>> q.append(4)

>>> q.popleft()
1
>>> q.popleft()
2

>>> q
deque([3, 4])
>>> len(q)
2

>>> q[0]
3
>>> q[-1]
4

Both append and popleft are $O(1)$, whereas looking for an element is $O(n)$, where $n$ is the size of the queue.