Deque in Python using Collections Module

Learn the basics of Deque in Python.

Deque is a double-ended queue. It can be used to add or remove elements from both the sides. In Python, we can use the collections.deque class to implement a deque.

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The deque class is a general-purpose, flexible and efficient sequence type that supports thread-safe, memory efficient appends and pops from either side. A deque provides approximately O(1) time complexity for append and pop opeations in either direction.

There are various built-in functions available in the collections module to perform the operations on the deque. Let's see how to use them.

from collections import deque

# Create a deque object
d = deque(['Black', 'White', 'Red', 'Green'])

# Add elements to the right side
d.append('Blue')
# deque(['Black', 'White', 'Red', 'Green', 'Blue'])

# Add elements to the left side
d.appendleft('Yellow')
# deque(['Yellow', 'Black', 'White', 'Red', 'Green', 'Blue'])

# Remove elements from the right side
d.pop()
# 'Blue'

# Remove elements from the left side
d.popleft()
# 'Yellow'

# Get the size of the deque
len(d)
# 5

In the above example, append() and pop() functions are used to add and remove elements from the right side of the deque. Similarly, appendleft() and popleft() functions are used to add and remove elements from the left side of the deque. len() function is used to get the size of the deque.

Let's see some more functions:

from collections import deque

# Create a deque object
queue = deque(['Black', 'White', 'Red', 'Green'])

# Extend the right side of the deque
queue.extend(['Blue', 'Yellow'])
# deque(['Black', 'White', 'Red', 'Green', 'Blue', 'Yellow'])

# Extend the left side of the deque
queue.extendleft(['Orange', 'Purple'])
# deque(['Orange', 'Purple', 'Black', 'White', 'Red', 'Green', 'Blue', 'Yellow'])

# Count the number of times an element appears in the deque
queue.count('Black')
# 1

# Insert an element at a given index
queue.insert(2, 'Brown')
# deque(['Orange', 'Purple', 'Brown', 'Black', 'White', 'Red', 'Green', 'Blue', 'Yellow'])

In the above example, extend() and extendleft() functions are used to add multiple elements at the same time to the right and left sides of the deque. count() function is used to count the number of times an element appears in the deque. insert() function is used to insert an element at a given index.

Conclusion¶

In this tutorial, we have learned the basics of Deque in Python using the collections module. We have also learned how to use the built-in functions available in the collections module to perform the operations on the deque. If you want to learn more about the deque class, you can refer to the official documentation of the collections module.