Python Deque Methods

In this post we’ll list Python Deque Methods. Ready? Let’s go! 🔥🔥🔥

A deque (double-ended queue) in Python is a type of list where elements can be added to or removed from both ends (front and back) efficiently. It is part of the collections module and is a more generalized form of stack and queue. Deques are thread-safe and can be used to implement both stacks and queues without the performance penalties associated with lists.

Here’s a list of the key methods used on a deque in Python, along with example code and a short description for each of the Python Deque Methods:

1. append(x) – Adds x to the right side of the deque.

from collections import deque
d = deque([1, 2, 3])
d.append(4)  # deque becomes [1, 2, 3, 4]

2. appendleft(x) – Adds x to the left side of the deque.

d.appendleft(0)  # deque becomes [0, 1, 2, 3, 4]

3. pop() – Removes and returns an element from the right side of the deque. Raises IndexError if empty.

d.pop()  # returns 4, deque becomes [0, 1, 2, 3]

4. popleft() – Removes and returns an element from the left side of the deque. Raises IndexError if empty.

d.popleft()  # returns 0, deque becomes [1, 2, 3]

5. extend(iterable) – Adds elements from iterable to the right side of the deque.

d.extend([4, 5])  # deque becomes [1, 2, 3, 4, 5]

6. extendleft(iterable) – Adds elements from iterable to the left side of the deque. Note that the iterable is added in reverse order.

d.extendleft([0, -1])  # deque becomes [-1, 0, 1, 2, 3, 4, 5]

7. rotate(n) – Rotate the deque n steps to the right. If n is negative, rotate to the left.

d.rotate(2)  # deque becomes [4, 5, -1, 0, 1, 2, 3]

8. maxlen – Maximum size of a deque or None if unbounded.

d = deque([1, 2, 3], maxlen=3)  # deque will not grow beyond length 3

9. clear() – Removes all elements from the deque.

d.clear()  # deque becomes empty

10. count(x) – Count the number of deque elements equal to x.

d = deque([1, 2, 3, 2, 4])
d.count(2)  # returns 2

11. index(x, [start, [stop]]) – Return the position of x in the deque (at or after index start and before index stop). Raises ValueError if not found.

d.index(3)  # returns 2

12. insert(i, x) – Insert x into the deque at position i.

d.insert(1, 'a')  # deque becomes [1, 'a', 2, 3, 2, 4]

13. remove(value) – Remove the first occurrence of value. Raises ValueError if not found.

d.remove('a')  # deque becomes [1, 2, 3, 2, 4]

14. reverse() – Reverse the elements of the deque in-place.

d.reverse()  # deque becomes [4, 2, 3, 2, 1]

15.copy() – Creates a shallow copy of the deque.

d_copy = d.copy()  # creates a copy of d

So there you have it, all 15 Python Deque Methods. The full code is as follows:

from collections import deque
d = deque([1, 2, 3])
d.append(4)  # deque becomes [1, 2, 3, 4]
d.appendleft(0)  # deque becomes [0, 1, 2, 3, 4]
d.pop()  # returns 4, deque becomes [0, 1, 2, 3]
d.popleft()  # returns 0, deque becomes [1, 2, 3]
d.extend([4, 5])  # deque becomes [1, 2, 3, 4, 5]
d.extendleft([0, -1])  # deque becomes [-1, 0, 1, 2, 3, 4, 5]
d.rotate(2)  # deque becomes [4, 5, -1, 0, 1, 2, 3]
d = deque([1, 2, 3], maxlen=3)  # deque will not grow beyond length 3
d.clear()  # deque becomes empty
d = deque([1, 2, 3, 2, 4])
d.count(2)  # returns 2
d.index(3)  # returns 2
d.insert(1, 'a')  # deque becomes [1, 'a', 2, 3, 2, 4]
d.remove('a')  # deque becomes [1, 2, 3, 2, 4]
d.reverse()  # deque becomes [4, 2, 3, 2, 1]
d_copy = d.copy()  # creates a copy of d

print(d)
print(d_copy)