In this tutorial, we will look at how to pop an element from the left 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 left 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 left of a deque in Python, use the popleft()
function. The following is the syntax –
# pop the left most element from deque, "queue" queue.popleft()
It removes the leftmost 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 left of a non-empty deque
First, let’s create a deque with some elements.
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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 left side of this deque object.
# pop the leftmost element val = queue.popleft() # print the poppend element print(val) # print the deque print(queue)
Output:
1 deque([2, 3])
Here, we used the popleft()
function to pop-out (remove) the leftmost value in the deque, queue
. You can see that it removes the leftmost value and returns it.
Example 2 – Pop element from the left 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 left using the popleft()
function.
# pop the leftmost element val = queue.popleft() # 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 leftmost element ----> 2 val = queue.popleft() 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.
You might also be interested in –
- Python – Convert a deque of strings to a single string
- Python – Convert a deque to a list
- Python – Get the Index of the Maximum Value in Deque
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- Python – Check If a Deque is Empty
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- Python – Count occurrences of a value in deque
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- 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 the End in Deque
- Python – Insert Element at a given Index in Deque
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