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Python Set add() Function

The Set add() method adds a single element to a set. If the element is already present in the set, the set remains unchanged.

note

The time complexity of the add() function is generally considered to be O(1) because sets in Python are implemented using a hash table.

Syntax​

my_set.add(element)

add() Parameters​

Python Set add() function parameters:

ParameterConditionDescription
elementRequiredThe element you want to add to the set.

add() Return Value​

Python Set add() function does not return any value: it modifies the set in-place.

Examples​

Example 1: Add an element to a Set​

For example, let's add a string to a set:

my_set = {'Tom', 'David', 'Ryan'}
my_set.add('Anna')

print(my_set) # Output: {'David', 'Anna', 'Tom', 'Ryan'}

output

{'David', 'Anna', 'Tom', 'Ryan'}
note

Your order of the words can be different since Set is an unordered collection!

Example 2: Add an element that already exists in a Set​

If you try to add an item that already exists in the set, the method does nothing.

For example, let's add the string 'Anna' to my_set:

my_set = {'Tom', 'David', 'Anna'}
my_set.add('Anna')

print(my_set) # Output: {'Anna', 'Tom', 'David'}

output

{'Anna', 'Tom', 'David'}

Example 3: Add a Tuple to a Set​

The item you want to add must be of immutable (unchangeable) type.

For example, you can add a Tuple to your set (since Tuples are immutable):

my_set = {'Tom', 'David', 'Anna'}
my_set.add((1, 2, 3))

print(my_set) # Output: {'David', 'Anna', (1, 2, 3), 'Tom'}

output

{'David', 'Anna', (1, 2, 3), 'Tom'}

Example 4: Add a List to a Set​

Attempting to add a list directly to a set using add() will result in a TypeError. This is because lists are mutable and thus not hashable, which is a requirement for set elements!

my_set = {1, 2, 3}
my_set.add([4, 5]) # This will raise a TypeError because lists are not hashable

output

Traceback (most recent call last):
  File "main.py", line 2, in <module>
    my_set.add([4, 5]) # This will raise a TypeError because lists are not hashable
TypeError: unhashable type: 'list'

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