Python Set

Python set is an unordered collection of items which are unique within that set. The order in which item in sets is placed is undefined. Sets are enclosed in brackets {} with items comma separated. Set is a mutable data type, so we can add or remove items from a set.

How to create a set in Python?

Set in Python is created using curly brackets {} with the items in the set be separated by a comma (,).  A set can have any number of items and can be of different data types. To have an idea of python data types, please refer to this tutorial:- Python Datatypes.

Let’s explore some of the examples of the set in the following example:-

a = {5, 2, 3, 1, 4}
days = {"Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday"}

# printing set variable
print("a = ", a)
print(days)

# data type of variable a
print(type(a))

The output of the above program is:-

How to change or add elements to a set in Python?

Since sets are mutable data types, you can add, edit or delete every item in a set. As a set is not indexable in Python, we cannot access any particular index of the item, so we need a function to add an item to set. We can add a single item using add() method and multiple using update() method in the set.

days = {"Sunday", "Monday"}
print("Current set", days)
days.add("Tuesday")
print("New set", days)
days.update({"Wednesday", "Thursday", "Friday"})
print("New set", days)

 How to delete or remove elements from a set in Python?

We can use discard() or remove() function to remove the item from a set. discard() function doesn’t throw error if the item is not found, whereas remove() function throws an error if the item is not found.

days = {"Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"}
print("Current set", days)
days.discard("Sunday")
print("Updated set", days)

How to iterate over a Set in Python?

A set can be iterated using for loop. Let us see the following example:-

days = {"Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"}
for day in days:
    print(day)

What is Python Frozenset?

Frozenset is an immutable set where set once defined cannot be changed. Sets are unhashable, so they can’t be used as dictionary keys. Frozensets are hashable and can be used as keys to a dictionary. This datatype supports methods like copy(), difference(), intersection(), isdisjoint(), issubset(), issuperset(), symmetric_difference() and union(). There are no methods as add or remove elements in a set. We can initialize frozen set as below:-

# initialize A and B
A = frozenset([1, 2, 3, 4])
B = frozenset([3, 4, 5, 6])

What are Python Set Operations?

Let’s use some examples to get an idea on set operations:-

A = {1, 2, 3, 4, 5}
B = {4, 5, 6, 7, 8}

print(A | B)  #Set Union
print(A & B)  #Set Intersection

#Alternate way
print(A.union(B))
print(A.intersection(B))

What are Python Set Built-in functions?

Python provides the following built-in functions which can be used with the sets.

What are Python Set built-in methods?

Python provides various methods that can help you perform the various operations in a set. Following are some of the built-in sets methods:-