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Python Sets

3 min read ·

Sets are one of Python’s built-in data types used to store multiple unique values in a single variable. They are unordered, mutable, and unindexed, making them ideal for fast membership testing and removing duplicates.
This topic covers sets from basics to practical usage.

What Is a Set?

A set is a collection that:
  • Stores unique elements only
  • Is unordered
  • Is mutable
  • Does not allow indexing

Set vs List vs Tuple

FeatureListTupleSet
OrderedYesYesNo
Allows duplicatesYesYesNo
MutableYesNoYes
IndexingYesYesNo

Creating Sets

Using Curly Braces {}

Using set() Constructor

Empty Set (Important)

This is NOT a set:

Access Set Items

Sets are unordered, so you cannot access items using indexes.

Check If Item Exists

Add Items to a Set

Add One Item – add()

Add Multiple Items – update()

Remove Items from a Set

remove() – Raises Error if Not Found

discard() – No Error if Not Found

pop() – Removes Random Item

clear() – Remove All Items

Set Length

Join Sets (Set Operations)

Union (| or union())

Intersection (& or intersection())

Difference (- or difference())

Symmetric Difference (^)

Set Comprehension

Frozen Set (Immutable Set)

Cannot modify:

Common Mistakes

Expecting Order in Sets

Order may change.

Using Mutable Items in Set

When to Use Sets

Use sets when:
  • You need unique values
  • Membership checking is frequent
  • Order does not matter
  • Removing duplicates is required