Hash Set in Python

Last Updated : 22 Sep, 2026

A Hash Set is a data structure that stores unique elements and provides efficient operations for adding, removing, and checking elements. Python's built-in set data type is an implementation of a hash set.

Python 
hs = {1, 2, 3, 4}

print(hs)

Output
{1, 2, 3, 4}

Explanation:

  • hs is created using curly braces.
  • The collection contains unique elements.
  • Hashing is used to efficiently store and find elements.

Important points:

  • Duplicate values are automatically removed.
  • Elements cannot be accessed using indexes.
  • The collection can be modified after creation.
  • Only hashable objects can be stored as elements.
  • Hashing provides efficient insertion, deletion, and membership checking.

Creating a Hash Set

A hash set can be created using curly braces {} or the set() constructor. The set() constructor can convert an iterable such as a list into a hash set.

Python 
hs = set([1, 2, 3, 3, 4])

print(hs)

Output
{1, 2, 3, 4}

Explanation:

  • The list contains 3 twice.
  • set() converts the list into a hash set.
  • The duplicate occurrence of 3 is removed

Operations on Hash Set

1. Adding Elements

The add() method is used to insert an element into a hash set.

Python 
hs = {1, 2, 3}
hs.add(4)
print("After Adding 4:", hs)

Output
After Adding 4: {1, 2, 3, 4}

Explanation:

  • hs initially contains three elements.
  • add(4) inserts 4 into the collection.
  • The updated collection contains four elements.

2. Removing Elements

The remove() and discard() methods are used to delete elements.

Python 
hs = {1, 2, 3, 4}

hs.remove(2)
hs.discard(5)

print(hs)

Output
{1, 3, 4}

Explanation:

  • remove(2) deletes 2 from the collection.
  • discard(5) does not raise an error because 5 is not present.
  • remove() raises a KeyError if the specified element does not exist.
  • discard() does not raise an error when the element is missing.

3. Using pop()

The pop() method removes and returns an arbitrary element.

Python 
hs = {1, 2, 3}

item = hs.pop()

print("Removed:", item)
print("Remaining:", hs)

Output
Removed: 1
Remaining: {2, 3}

Explanation:

  • pop() removes one element from the collection.
  • The removed element is stored in item.
  • The removed element should not be assumed to be a specific value because the collection is unordered.

4. Checking for an Element

The in operator is used to check whether an element exists.

Python 
hs = {10, 20, 30}

print(20 in hs)

Output
True

Explanation:

  • 20 in hs checks whether 20 exists in the collection.
  • Since 20 is present, the expression returns True.
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