Stacks and Queues (basic data structures)

This lesson covers the difference between two fundamental data structures, stacks and queues, and how to implement each in Python. It's written for anyone searching "Python stack queue implementation" or "Python deque tutorial".

A stack is "last in, first out" — the most recently added item comes out first. A queue is "first in, first out" — the earliest item added comes out first. Think of the difference between a stack of books and a line of people. In Python, you can efficiently implement a stack with a list's append() and pop(), and a queue with collections.deque.

The sample code implements a stack by adding to the end with a list's .append() and removing from the end with .pop(), and a queue using deque's .append() and .popleft(). deque stands for "double-ended queue" — a dedicated data structure that can remove items from the front much faster than a plain list.

A common beginner mistake is trying to implement a queue with a list using .pop(0). It technically works, but it gets slow as the data grows, so using deque for queues is the standard real-world practice. Which data structure you choose significantly affects the order of processing and the efficiency of your algorithm.

A browser's "back" button behaves like a stack, while a print queue or a line of waiting tasks behaves like a queue — these fundamental data structures quietly power a lot of familiar mechanisms.