Set add() Method in Python

The Python set add() method adds a given element to a set if the element is not present in the set in Python.

Example: Add Element to an Empty set

It is used to add a new element to the empty set.

Python3

GEEK = set()
GEEK.add('s')
print("Letters are:", GEEK)

# adding 'e' again
GEEK.add('e')
print("Letters are:", GEEK)
# adding 's' again
GEEK.add('s')
print("Letters are:", GEEK)

Output

Letters are: {'s'}
Letters are: {'e', 's'}
Letters are: {'e', 's'}

Set add() Syntax

Syntax: set.add( elem )

Parameters

• elem: The element that needs to be added to a set.

Return

The add() method does not return anything 

What is set add() Method

In Python, a set is an unordered collection of unique elements. The add() method is a built-in method in Python that is used to add a single element to a set. If the element is already present in the set, the set remains unchanged.

Python Set add() Method Examples

Before going to the example we are assuming the time complexity of the set.add() function is O(1) because the set is implemented using a hash table.

Now let’s look at some use cases of add() function in Python with examples:

• Add Element to an Empty set
• Add a new element to a Python set
• Add an element in a set that already exists
• Adding any iterable to a set

1. Add Element to an Empty set

It is used to add a new element to the empty set.

Python3

GEEK = set()
GEEK.add('s')
print("Letters are:", GEEK)

# adding 'e' again
GEEK.add('e')
print("Letters are:", GEEK)
# adding 's' again
GEEK.add('s')
print("Letters are:", GEEK)

Output

Letters are: {'s'}
Letters are: {'e', 's'}
Letters are: {'e', 's'}

2. Add a new element to a Python set

It is used to add a new element to the set if it is not existing in a set.

Python3

# set of letters
GEEK = {'g', 'e', 'k'}

# adding 's'
GEEK.add('s')
print("Letters are:", GEEK)

# adding 's' again
GEEK.add('s')
print("Letters are:", GEEK)

Output:

Letters are: {'e', 's', 'g', 'k'}
Letters are: {'e', 's', 'g', 'k'}

3. Add element in a set that already exists

It is used to add an existing element to the set if it is existing in the Python set and check if it gets added or not.

Python3

# set of letters
GEEK = {6, 0, 4}

# adding 1
GEEK.add(1)
print('Letters are:', GEEK)

# adding 0
GEEK.add(0)
print('Letters are:', GEEK)

Output:

Letters are: {0, 1, 4, 6}
Letters are: {0, 1, 4, 6}

4. Adding any iterable to a set

We can add any Python iterable to a set using Python add or Python update function, if we try to add a list using the add function we get an unhashable Type error.

Python3

# Python code to demonstrate addition of tuple to a set.
s = {'g', 'e', 'e', 'k', 's'}
t = ('f', 'o')
l = ['a', 'e']

# adding tuple t to set s.
s.add(t)

# adding list l to set s.
s.update(l)

print(s)

Output :

{'a', 'g', 'k', 'e', ('f', 'o'), 's'}

In this article we covered the add() function in Python. Set add() method in Python is useful to avoid entry of duplicate item in the set.

Read More on Set Methods