Sets

A set is a bag of unique items.

If you drop in two of the same thing, only one stays.

Sets do not keep a fixed order like a neat shelf.

They are great for membership checks and removing copies.

Creating a set

Use curly braces with values, or use set().

An empty set must be set(), because {} makes an empty dict.

Add and remove

add puts one item in.

remove takes one out and errors if missing.

discard takes one out and stays quiet if missing.

Membership

Ask if an item is in the bag with in.

This is fast and easy to read.

Set math

Sets can combine like groups of stickers.

Removing duplicates from a list

Turn a list into a set, then back into a list.

Order may change. That is okay when order does not matter.

When to use a set

Use a set when uniqueness matters.

Use a list when order and duplicates matter.

Use a dict when each item needs a label and a value.

Tip: Remember {} is an empty dict. Use set() when you need an empty set.