Python – Get the First and Last Element in a Deque

In this tutorial, we will look at how to get the first and the last element in a deque in Python (without deleting any elements) with the help of some examples.

deque in Python

The collections module in Python comes with a deque class that you can use to implement a stack or queue data structure in Python. Deques support thread-safe, memory efficient appends and pops from either side of the deque with approximately the same O(1) performance in either direction.

In simple terms, you can think of a deque in Python as a list-like data structure but with efficient insertion and removal of items from either end (left and right). This makes them very useful when implementing a stack or queue functionality in Python.

How to get the first and the last element in a deque in Python?

Deques in Python make it very easy to add and remove elements from either end.

You can use the pop() function to get the last element in the deque and the popleft() function to get the first element in the deque but these methods modify the deque by removing the concerned element.

What if you just want to get the first and/or the last element without modifying the deque object?

Similar to lists, deques in Python are indexed starting from 0 and thus you can use the index 0 to get the first element and the index -1 to get the last element in a deque.

The following is the syntax –

# get the first element in the deque "queue" 
queue[0]
# get the last element in the deque "queue" 
queue[1]

This is similar to how you’d get the first and last values in any ordered iterable in Python.

Examples

Let’s now look at some examples of using the above syntax

First, let’s create a deque with some elements.

from collections import deque

# create a deque
queue = deque([1, 2, 3])
# print the deque
print(queue)

Output:

deque([1, 2, 3])

Here, we imported the deque class from the collections module and created a deque object, queue with some numbers. You can see that the deque contains three values 1, 2, and 3.

Example 1 – Get the first element in a deque

To get the first element in a deque, access the value at the index 0 using [] notation.

# first value in the deque
print(queue[0])

Output:

1

We get the first value in the deque, queue as 1.

Example 2 – Get the last element in a deque

To get the last element in a deque, access the value at the last index (using a negative index can be helpful here). The index -1 represent the index of the last value.

# last value in the deque
print(queue[-1])

Output:

3

We get the last value in the deque, queue as 3.

You might also be interested in –

• Python – Count occurrences of a value in deque
• Python – Create a deque copy
• Python – Rotate a Deque to the Right and Left
• Python – Extend deque to the left
• Python – Extend deque to the right
• Python – Get the Max Size of a Deque
• Python – Reverse a deque
• Python – Get Index of a Value in Deque
• Python – Remove Element by Value in Deque
• Python – Remove all elements from a deque (clear deque)
• Python – Append Element to a Deque
• Python – Append Element to the Left in Deque
• Python – Pop Element From Left in Deque
• Python – Pop Element From the End in Deque
• Python – Insert Element at a given Index in Deque