Python – Pop Element From the End in Deque

In this tutorial, we will look at how to pop an element from the end of a deque in Python 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 pop an element from the end of a deque in Python?

The deque class comes with a number of built-in functions to help perform common operations (like adding and removing elements).

To pop (remove) an element from the end of a deque in Python, use the pop() function. The following is the syntax –

# pop the right most element from deque, "queue"
queue.pop()

It removes the last (rightmost) element from the deque and returns it. If no elements are present in the deque, it raises an IndexError.

Examples

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

Example 1 – Pop element from the end of a non-empty deque

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 three elements – 1, 2, and 3.

Now, let’s pop an element from the end (right side) of this deque object.

# pop the last (rightmost) element
val = queue.pop()
# print the poppend element
print(val)
# print the deque
print(queue)

Output:

3
deque([1, 2])

Here, we used the pop() function to pop-out (remove) the last value in the deque, queue. You can see that it removes the rightmost value and returns it.

Example 2 – Pop element from the end of an empty deque

Let’s now create an empty deque object (a deque with no elements).

# create an empty deque
queue = deque()
# print the deque
print(queue)

Output:

deque([])

Now, let’s try to remove an element from the end of this deque using the pop() function.

# pop the last (rightmost) element
val = queue.pop()
# print the poppend element
print(val)
# print the deque
print(queue)

Output:

---------------------------------------------------------------------------
IndexError                                Traceback (most recent call last)
Input In [4], in <module>
      1 # pop the last (rightmost) element
----> 2 val = queue.pop()
      3 # print the poppend element
      4 print(val)

IndexError: pop from an empty deque

You can see that we get an IndexError. This happened because we are trying to remove an element from an empty deque object (which does not have any elements).

Difference between popleft() and pop()

Both the popleft() and the pop() functions are used to remove an element from a deque in Python. The main difference between them is that the pop() function is used to remove an element from the end (the right side) of the deque whereas the popleft() function is used to remove an element from the start (the left side) of the deque.

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