Set Mathematical Operations

Sets let you perform Venn diagram math operations easily: combining collections, finding shared items, or finding items that exist in only one group.

Union (| or .union())

A Union combines all unique items from both sets together into one big set:

frontend = {"HTML", "CSS", "JavaScript"}
backend = {"Python", "SQL", "JavaScript"}

# Combine both teams
fullstack = frontend | backend
print(fullstack)  # Output: {'HTML', 'CSS', 'JavaScript', 'Python', 'SQL'}

Intersection (& or .intersection())

An Intersection finds only the items that exist inside both sets at the same time:

frontend = {"HTML", "CSS", "JavaScript"}
backend = {"Python", "SQL", "JavaScript"}

# Find overlapping skills
shared_skills = frontend & backend
print(shared_skills)  # Output: {'JavaScript'}

Difference (- or .difference())

A Difference finds items that are inside the first set, but NOT in the second set:

frontend = {"HTML", "CSS", "JavaScript"}
backend = {"Python", "SQL", "JavaScript"}

# Skills unique to frontend only
only_frontend = frontend - backend
print(only_frontend)  # Output: {'HTML', 'CSS'}

Symmetric Difference (^ or .symmetric_difference())

A Symmetric Difference finds items that exist in one set or the other, but not in both:

frontend = {"HTML", "CSS", "JavaScript"}
backend = {"Python", "SQL", "JavaScript"}

non_overlapping = frontend ^ backend
print(non_overlapping)  # Output: {'HTML', 'CSS', 'Python', 'SQL'}

Common Beginner Mistakes

Using + operator to combine sets

# Wrong - sets do not support addition using +
set1 = {1, 2}
set2 = {3, 4}
combined = set1 + set2  # TypeError!

# Right - use the union pipe | operator or .union() method
combined = set1 | set2

What's Next?

Let's transition to Module 11: Dictionaries to learn how to store labeled information using key-value pairs.

Module 11: Dictionaries

Learn how to store contact details, settings, and user profiles using keys and values