Data Structure: Stack

Lesson

Part 1 — what a stack is, its operations, and how to build one with a Python list.

In this lesson you will

Explain a stack as a last in, first out data structure with one open end, the top
Perform push, pop and peek, and test for an empty stack, using a Python list
Detect underflow and explain overflow for fixed-size stacks
Trace the contents of a stack after a sequence of operations

Part 1 at a glance

Concept

Data structures

A data structure organises data so that it can be stored and used efficiently. Each structure has its own rules for adding and removing items.

A data structure is a way of organising data so that it can be used efficiently.
Structure	How items are added and removed	Everyday picture
List	At any position, by index	A numbered register
Stack	Only at one end, the top (LIFO)	A pile of plates
Queue	Added at the rear, removed from the front (FIFO)	A ticket-counter line
Dictionary	By key	A phone directory

Diagram

Each column is the stack after one operation; arrows show the value returned.

In a stack, insertion and deletion happen at one end, the top. The item added last is removed first: LIFO (Last In, First Out).