IndexError: pop from Empty Deque in Python

In Python, the IndexError: pop from an empty deque is an error that occurs when trying to use the pop() method on an empty deque. A deque (double-ended queue) is a versatile data structure that allows efficient addition and removal of elements from both ends. This article explores the causes of the error, provides examples of its occurrence, and offers solutions to handle it effectively.

What is IndexError: Pop From An Empty Deque Error in Python?

The IndexError: pop from an empty deque error arises when the pop() method is called on a deque that has no elements. Since pop() removes and returns an element from the right end of the deque, attempting this operation on an empty deque leads to an index error.

Reason for Indexerror: Pop From An Empty Deque Error

Below are some of the reasons due to which Indexerror: Pop From An Empty Deque occurs in Python:

• Attempting to Pop From an Empty Deque
• Popping from an Empty Deque Inside a Loop
• Using Pop Method Without Error Handling

Attempting to Pop From an Empty Deque

In this code, an attempt is made to pop an element from an empty deque, leading to the IndexError: pop from an empty deque. The deque is not checked for emptiness before the pop operation, causing the error.

Python3

from collections import deque

empty_deque = deque()
result = empty_deque.pop()

Output:

Hangup (SIGHUP)
Traceback (most recent call last):
  File "Solution.py", line 4, in <module>
    result = empty_deque.pop() 
IndexError: pop from an empty deque

Popping from an Empty Deque Inside a Loop

In this code, an attempt is made to pop elements from an empty deque inside a loop, resulting in the IndexError: pop from an empty deque. The loop structure does not account for the deque’s emptiness.

Python3

from collections import deque

empty_deque = deque()

for _ in range(3):
    result = empty_deque.pop()

Output:

Hangup (SIGHUP)
Traceback (most recent call last):
  File "Solution.py", line 4, in <module>
    result = empty_deque.pop() 
IndexError: pop from an empty deque

Using pop() Method Without Error Handling

In this code, the pop() method is used without error handling, leading to the IndexError when attempting to pop from an empty deque. The absence of a check results in an unhandled error.

Python3

from collections import deque

my_deque = deque()

result = my_deque.pop()

Output:

Hangup (SIGHUP)
Traceback (most recent call last):
  File "Solution.py", line 4, in <module>
    result = empty_deque.pop() 
IndexError: pop from an empty deque

Fix Indexerror: Pop From An Empty Deque Error

Below are some of the approaches to solve this error in Python:

• Checking if the Deque is Not Empty Before Popping
• Checking Deque Size Before Popping Inside a Loop
• Using a Try/Except Block to Handle the Error

Checking if the Deque is Not Empty Before Popping

To resolve the issue, we check if the deque my_deque is not empty before attempting to use the pop() method. If the deque is empty, a message is displayed indicating its emptiness, preventing the IndexError.

Python3

from collections import deque

my_deque = deque()

if my_deque:
    result = my_deque.pop()
    print(result)
else:
    print('The deque is empty')

Output

The deque is empty

Checking Deque Size Before Popping Inside a Loop

To address the problem, we check if the deque has elements before attempting to pop inside the loop. If the deque is empty, a message is displayed, preventing the IndexError within the loop.

Python3

from collections import deque

my_deque = deque()

for _ in range(3):
    if my_deque:
        result = my_deque.pop()
        print(result)
    else:
        print('The deque is empty')

Output

The deque is empty
The deque is empty
The deque is empty

Using a Try/Except Block to Handle the Error

To tackle the issue, we employ a try/except block to catch the IndexError. If the pop operation on the deque raises an IndexError, the exception is caught, and a message is printed, handling the error gracefully.

Python3

from collections import deque

my_deque = deque()

try:
    result = my_deque.pop()
    print(result)
except IndexError:
    print('The deque is empty')

Output

The deque is empty