Sets

A set is an unordered collection of unique items. No duplicates, no indexes.

Create a set

python
thisset = {"apple", "banana", "cherry"}
print(thisset)

Set properties

• Unordered: items have no defined order; you can't index them.
• Unchangeable: you can't change an item, but you can add/remove items.
• No duplicates: the same value appears only once.
• Unindexed: thisset[0] raises a TypeError.

Duplicates are dropped

python
thisset = {"apple", "banana", "cherry", "apple"}
print(thisset)

### {'apple', 'banana', 'cherry'}

Check length

python
print(len(thisset))

### 3

Set items can be any type

But they must be hashable, so no lists or dicts inside a set.

Membership test

in is the fastest way to check a set:

python
print("banana" in thisset)

### True

A note on order

Since sets are unordered, printing one may show items in any order.

TL;DR

• Sets use { } with no key-value pairs.
• Unordered, unindexed, no duplicates.
• Items must be hashable (no lists/dicts).
• in checks membership quickly.