Day 17: Sets — No Duplicates Allowed!

What's a Set?

Imagine a VIP guest list at a party. Rohith tries to enter twice — security spots it and removes the duplicate. Only one Rohith gets in! That's exactly how a set works. Add the same item twice and it automatically keeps only one copy!

Creating a Set

fruits = {"Apple", "Mango", "Apple"}
print(fruits)

Output: {'Apple', 'Mango'}. You added Apple twice but the set kept only one. Duplicates removed automatically — no extra code needed!

Real World Connection

Instagram counts unique viewers on a story — if you watch it 10 times, you're still counted once. Spotify tracks unique songs in your library — no duplicates. Online exams track unique students who attempted — sets do this automatically!

Adding and Removing

users = {"Priya", "Sam", "Rohith"}

users.add("Arjun")      # add new user
users.remove("Sam")     # remove a user

print(users)

Output: {'Priya', 'Rohith', 'Arjun'}. add() and remove() work just like lists. But try adding "Priya" again — it won't duplicate!

Looping Through a Set

fruits = {"Apple", "Mango", "Banana"}

for fruit in fruits:
    print(fruit)

Works just like looping a list! But notice — sets have no fixed order. Items may print in any order each time. That's fine when you just need every unique item!

Common Mistakes

Mistake 1 — Expecting duplicates to stay.

fruits = {"Apple", "Apple", "Mango"}
print(fruits)   # {'Apple', 'Mango'} — one Apple only!

Mistake 2 — Using index positions like a list.

fruits[0]              # WRONG — sets have no positions!

for fruit in fruits:
    print(fruit)       # CORRECT — loop through instead!

Mini Challenge

Quick Quiz

Q: I add "Mango" to a set that already has "Mango". How many Mangos are in the set? A: Just one! Sets never keep duplicates.

Q: Can you access a set item using fruits[0]? A: No! Sets have no positions. Use a loop instead.

Q: List, Tuple or Set — which one removes duplicates automatically? A: Set!

Key Takeaways