Python - Sets

Overview

Estimated time: 15–25 minutes

Use sets for fast membership tests and deduplication. Learn basic operations and typical patterns.

Learning Objectives

• Create sets and perform union, intersection, difference, symmetric difference.
• Use set comprehensions.
• Understand hashability and why elements must be immutable.

Prerequisites

• Python - Dictionaries

Basics and operations

a = {1, 2, 3}
b = {3, 4}
print(2 in a)
print(a | b, a & b, a - b, a ^ b)

Deduplication

data = [1, 2, 2, 3]
print(list(set(data)))

Common Pitfalls

• Lists are unhashable; use tuples for compound members: {(x, y)}.
• Set literals require braces; empty set is set() not {} (that’s an empty dict).

Checks for Understanding

1. How do you compute the intersection of two sets?
2. Why can’t you put a list into a set?

Exercises

1. Given two lists, print common unique elements using sets.
2. Use a set to check if a string has duplicate characters.