Deque in Python

The Deque is another name for a double-ended queue, in python, we can implement deque by using a collection module.

In a deque, we can add or remove the elements from both ends, these are called append and pop operations.

In a deque, every append operation provides the 0(1) tie complexity and every pop operation provides the 0(n) time complexity.

Deque Operations

Examples

This is a basic example showing several operations

We create a basic deque collection with 3 items.

We then append an item to the left and then right and then removing them and the reverse the deque

import collections
# Create a deque
mydeque = collections.deque(["Mar","Apr","Jun"])
print (mydeque)

# Append to the right
print("Adding to the right: ")
mydeque.append("Jul")
print (mydeque)

# Append to the left
print("Adding to the left: ")
mydeque.appendleft("Feb")
print (mydeque)

# Remove from the right
print("Removing from the right: ")
mydeque.pop()
print (mydeque)

# Remove from the left
print("Removing from the left: ")
mydeque.popleft()
print (mydeque)

# Reverse the dequeue
print("Reversing the deque: ")
mydeque.reverse()
print (mydeque)

This is what was displayed

>>> %Run dequeexample1.py
deque(['Mar', 'Apr', 'Jun'])
Adding to the right: 
deque(['Mar', 'Apr', 'Jun', 'Jul'])
Adding to the left: 
deque(['Feb', 'Mar', 'Apr', 'Jun', 'Jul'])
Removing from the right: 
deque(['Feb', 'Mar', 'Apr', 'Jun'])
Removing from the left: 
deque(['Mar', 'Apr', 'Jun'])
Reversing the deque: 
deque(['Jun', 'Apr', 'Mar'])

This example demonstrates the following insert(), index(), remove(), count()

# demo of insert(), index(), remove(), count()
import collections
 
# initialize deque
mydeque = collections.deque([1, 2, 3, 3, 4, 2, 4, 1 , 2, 3, 4])
 
# using index() to print the first occurrence of 4
print ("The number 3 first occurs at a position : ")
print (mydeque.index(3,2,5))
 
# using insert() to insert the value 4 at 7th position
mydeque.insert(6,4)
 
# printing deque
print ("The deque after inserting 4 at 7th position is : ")
print (mydeque)
 
# using count() to count the occurrences of 3
print ("The count of 4 in deque is : ")
print (mydeque.count(4))
 
# using remove() to remove the first occurrence of 3
mydeque.remove(4)
 
# printing modified deque
print ("The deque after deleting first occurrence of 4 is : ")
print (mydeque)

Which displays the following

>>> %Run dequeexample2.py
The number 3 first occurs at a position : 
2
The deque after inserting 4 at 7th position is : 
deque([1, 2, 3, 3, 4, 2, 4, 4, 1, 2, 3, 4])
The count of 4 in deque is : 
4
The deque after deleting first occurrence of 4 is : 
deque([1, 2, 3, 3, 2, 4, 4, 1, 2, 3, 4])