Python Set


Sets are used to store multiple items in a single variable.

Set is one of 4 built-in data types in Python used to store collections of data, the other 3 are List, Tuple, and Dictionary, all with different qualities and usage.

A set is a collection which is both unordered and unindexed.

Sets are written with curly brackets.


Create a Set:

thisset = {"apple", "banana", "cherry"}

Note: Sets are unordered, so you cannot be sure in which order the items will appear.

Set Items

Set items are unordered, unchangeable, and do not allow duplicate values.


Unordered means that the items in a set do not have a defined order.

Set items can appear in a different order every time you use them, and cannot be referred to by index or key.


Sets are unchangeable, meaning that we cannot change the items after the set has been created.

Once a set is created, you cannot change its items, but you can add new items.

Duplicates Not Allowed

Sets cannot have two items with the same value.


Duplicate values will be ignored:

thisset = {"apple", "banana", "cherry", "apple"}


Get the Length of a Set

To determine how many items a set has, use the len() method.

Sets in Python

A Set is an unordered collection data type that is iterable, mutable and has no duplicate elements. Python’s set class represents the mathematical notion of a set. The major advantage of using a set, as opposed to a list, is that it has a highly optimized method for checking whether a specific element is contained in the set. This is based on a data structure known as a hash table. Since sets are unordered, we cannot access items using indexes like we do in lists.

 # Python program to
# demonstrate sets
# Same as {"a", "b", "c"}
myset =set(["a", "b", "c"])
# Adding element to the set
{'c', 'b', 'a'}
{'d', 'c', 'b', 'a'}

Frozen Sets

Frozen sets in Python are immutable objects that only support methods and operators that produce a result without affecting the frozen set or sets to which they are applied. While elements of a set can be modified at any time, elements of the frozen set remain the same after creation.If no parameters are passed, it returns an empty frozenset.

 # Python program to demonstrate differences
# between normal and frozen set
# Same as {"a", "b","c"}
normal_set =set(["a", "b","c"])
print("Normal Set")
# A frozen set
frozen_set =frozenset(["e", "f", "g"])
print("\nFrozen Set")
# Uncommenting below line would cause error as
# we are trying to add element to a frozen set
# frozen_set.add("h")

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