Why sets are used in Python

Introduction

Sets are used to store unique items and to quickly check if something is in a group. They help remove duplicates and make some tasks faster.

When you want to remove duplicate items from a list of things.

When you need to check if an item exists in a collection quickly.

When you want to find common items between two groups.

When you want to combine two groups but keep only unique items.

When you want to find items that are in one group but not in another.

Syntax

Python

my_set = {item1, item2, item3}
# or
my_set = set([item1, item2, item3])

Sets use curly braces {} or the set() function to create.

Items in a set are unique and unordered.

Examples

Create a set of fruits with unique names.

Python

fruits = {'apple', 'banana', 'orange'}

Creates a set from a list with duplicates; duplicates are removed.

Python

numbers = set([1, 2, 2, 3, 4])
print(numbers)

Finds common items between two sets using & operator.

Python

a = {1, 2, 3}
b = {2, 3, 4}
common = a & b
print(common)

Sample Program

This program shows how sets remove duplicates, check membership, and perform union, intersection, and difference operations.

Python

items = ['apple', 'banana', 'apple', 'orange', 'banana']
unique_items = set(items)
print('Unique items:', unique_items)

if 'apple' in unique_items:
    print('Apple is in the set')

set_a = {1, 2, 3}
set_b = {3, 4, 5}
print('Union:', set_a | set_b)
print('Intersection:', set_a & set_b)
print('Difference:', set_a - set_b)

Important Notes

Sets do not keep the order of items like lists do.

You cannot have mutable items like lists inside a set.

Sets are very fast for checking if an item exists.

Summary

Sets store unique items only.

They help remove duplicates easily.

Sets support fast membership tests and set operations like union and intersection.