Python deque

Python deque is similar to list and has had many useful methods since Python 3.5.

from collections import deque

d = deque()

d.append(1)
d.append(2)

print(d)  # deque([1, 2])

The deque object can be handled like a list.

from collections import deque

d = deque()

d.append(1)
d.append(2)
d.append(3)

d.reverse()

print(d)  # deque([3, 2, 1])

d.clear()

print(d)  # deque([])

Insert an object at the first position

from collections import deque

d = deque([1, 2, 3])
print(d)  # deque([1, 2, 3])

d.appendleft(5)
print(d)  # deque([5, 1, 2, 3])

The appendleft() is a very useful method of deque. It inserts 5 at the first position and all the indexes move. This kind of updating costs the memory in list.