What is the difference between a stack data structure and a queue?

A stack and a queue are data structures for storing elements with different access rules.

• Stack operates on the LIFO (Last In, First Out) principle — the last added element is retrieved first. Imagine a stack of plates: you take the top one.

• Queue operates on the FIFO (First In, First Out) principle — the first added element is retrieved first. It's similar to a line in a store: the first to arrive is the first to be served.

In Python, a stack can be implemented using a list with the append() and pop() methods. A queue is more conveniently implemented using collections.deque.

Example of a stack:

stack = []
stack.append(1)  # add
stack.append(2)
print(stack.pop())  # retrieve 2

Example of a queue:

from collections import deque
queue = deque()
queue.append(1)  # add
queue.append(2)
print(queue.popleft())  # retrieve 1