What is the difference between a stack and a queue in Python?

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Jayant Kumar · Accepted Answer

In Python, a stack and a queue are both data structures used to organize and manipulate collections of elements. However, they have distinct characteristics and operate on different principles:
Stack:

A stack is a Last-In-First-Out (LIFO) data structure.
Elements are added and removed from only one end, known as the "top" of the stack.
The last element added to the stack is the first one to be removed.
Common stack operations include:

Push: Adds an element to the top of the stack.
Pop: Removes and returns the element from the top of the stack.
Peek: Returns the element at the top of the stack without removing it.

Python's list type can be used as a basic stack by using the append() method to push elements and the pop() method to remove elements from the end.

Queue:

A queue is a First-In-First-Out (FIFO) data structure.
Elements are added to one end, known as the "rear" or "back" of the queue, and removed from the other end, known as the "front" or "head" of the queue.
The first element added to the queue is the first one to be removed.
Common queue operations include:

Enqueue or Push: Adds an element to the rear of the queue.
Dequeue or Pop: Removes and returns the element from the front of the queue.
Peek: Returns the element at the front of the queue without removing it.

Python's collections.deque class can be used as a basic queue. The append() method adds elements to the rear, and the popleft() method removes elements from the front.

Here's an example to demonstrate the difference between a stack and a queue in Python:
# Stack example
stack = []
stack.append(1)
stack.append(2)
stack.append(3)
print(stack.pop())  # Output: 3

# Queue example
from collections import deque
queue = deque()
queue.append(1)
queue.append(2)
queue.append(3)
print(queue.popleft())  # Output: 1

In this example, when using a stack, the last element added (3) is the first one to be removed. In contrast, when using a queue, the first element added (1) is the first one to be removed.
Stacks are often used for tasks such as tracking function calls, evaluating expressions, or implementing undo/redo operations. Queues, on the other hand, are useful for handling tasks that follow a First-In-First-Out (FIFO) order, such as handling incoming requests or implementing a breadth-first search algorithm.

What is the difference between a stack and a queue in Python?

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What is the difference between a stack and a queue in Python?

Jayant Kumar @jayantkumar314

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