Check if Set is Empty in Python [3 Best Ways]

Creating a set and checking if it is empty or not in python is simple and straightforward. In this article, we’ll look at how to create an empty set and the methods to check if set is empty in Python. Let’s first quickly go over what sets and when they are efficient and useful.

(If you already have the complete basics of sets, please feel free to skip the initial introductory sections and go to the creation of empty sets section.)

Set data type in Python

One of Python’s five built-in data types, called Set, is used to store collections of unique, unordered, mutable, and Iterable data.

1. Unique: Set holds only unique elements in it by not allowing any duplicate Elements
2. Unordered: Insertion order in sets is not preserved as the index of each new element will be calculated using a hash function.
3. Mutable: We can add or remove set items, but we can’t access or update elements. Because set elements are not indexed like lists and tuples. As a result, you can’t access elements of the set using an index.
4. Iterable: We can iterate through set elements in python.

Creating an empty Set in Python

a) Creating a set with elements

To create a set in python, we have to surround elements with curly braces { }.

social_media_sites = {'Facebook', 'Instagram', 'Twitter', 'Linkedin', 'Pinterest', 'Snapchat'}

print("social media sites:", social_media_sites)

Output:

social media sites: {'Instagram', 'Facebook', 'Linkedin', 'Pinterest', 'Snapchat', 'Twitter'}

But unlike lists and tuples, we can’t create empty sets using empty curly braces because it will be treated as a dictionary with empty key-value pairs.

empty_list = []
print(type(empty_list))

empty_tuple = ()
print(type(empty_tuple))

empty_dict = {}
print(type(empty_dict))

Output:

<class 'list'>
<class 'tuple'>
<class 'dict'>

We can create an empty set in python using the set() function.

set() function in python: It takes an iterable object as input and converts it into a set. If we don't pass anything to it, it will return an empty set.

b) Empty set creation

Now, Let’s see the code to create an empty set in python.

empty_set = set()

print(type(empty_set))
print(empty_set)

Output:

<class 'set'>
set()

Till now, we have seen the creation of an empty set. Now, let’s see how to check if a set is empty.

How to check if set is empty or not

There are 3 ways using which we can check if set is empty in python.

Method 1: Using len() function

In this method, we’ll get the length of a set using len() function. If its length is 0, the set is empty false otherwise.

def is_empty(set_in_python):
    set_length = len(set_in_python)
    if set_length == 0:
        return True
    else:
        return False

empty_set = set()
non_empty_set = {1, 2, 3}

print("is set '", empty_set, "' empty?", is_empty_c(empty_set))
print("is set '", non_empty_set, "' empty?", is_empty_c(non_empty_set))

Output:

is set ' set() ' empty? True
is set ' {1, 2, 3} ' empty? False

Method 2: Using boolean context

The boolean context in python returns always True for non-empty collections and False for empty collections.

def is_empty(python_set):
    # boolean context will be True for non-empty collection
    if bool(python_set):
        # returning False for is_empty as the collection is not empty
        return False
    else:
        # return True for is_empty as the collection is empty
        return True


empty_set = set()
non_empty_set = {1, 2, 3}

print("is set '", empty_set, "' empty?", is_empty_c(empty_set))
print("is set '", non_empty_set, "' empty?", is_empty_c(non_empty_set))

Output:

is set ' set() ' empty? True
is set ' {1, 2, 3} ' empty? False

Method 3: Comparing with another empty set

Here in this example, we’ll create one empty set and compare it with the given set. If both are equal, the set is empty false otherwise.

def is_empty(python_set):
    empty_set = set()
    if python_set == empty_set:
        return True
    else:
        return False

empty_set = set()
non_empty_set = {1, 2, 3}

print("is set '", empty_set, "' empty?", is_empty_c(empty_set))
print("is set '", non_empty_set, "' empty?", is_empty_c(non_empty_set))

Output:

is set ' set() ' empty? True
is set ' {1, 2, 3} ' empty? False

Bottom Line

Though all the 3 methods are simple and easy to implement, we would recommend using the len() function, as it makes the code more readable than Using the boolean context as sometimes we get confused with its implementation.

Avoid creating another empty set as we did in Method 3 – Comparing with another empty set. This is not the standard way of checking if set is empty Python.

Note: We can get the length of sequence data types in constant time O(1) using the len() function whether its length is 10 or 10 million. The reason is they maintain a data member which holds the length of its data type and it will be altered when the element is added or removed. The len() function in python, just access this stored member to get the length.

More about Sets in Python

Till now we have seen how to create a set and how to check if it’s empty or not. In this section, let’s see a few of the important things to know about sets.

Sets are more efficient!

In programming, choosing the right data types that are more efficient is important. In the below scenarios, sets work more effectively than other built-in data types of python.

1. To store unique elements in a collection.
2. To do a membership test of an element in the collection using the ‘in’ operator. 
3. To do Mathematical operations like union, intersection, and difference. 

Watch this video on hash tables to know more about them.

Set Operations:

Here We’ll discuss the main set operations such as union, intersection, difference, subset, and superset with examples.

For all the examples, we will use the below variables.

jack_amazon_cart = {'iPod', 'Smart tv', 'Spectacles', 't-shirt'}
jenny_amazon_cart = {'iPhone', 'Spectacles', 'Headphones', 'frock'}

a) Union

Returns all unique elements from both sets.

# Union Operation - Returns all unique elements from both sets
print("Union of ", jack_amazon_cart, " and ", jenny_amazon_cart, " is", end=" ")
print(jack_amazon_cart | jenny_amazon_cart)

Output:

Union of  {'Smart tv', 'iPod', 'Spectacles', 't-shirt'}  and  {'iPhone', 'Headphones', 'Spectacles', 'frock'}  is {'Headphones', 'iPod', 'Spectacles', 't-shirt', 'iPhone', 'Smart tv', 'frock'}

b) Intersection

Returns common elements from both sets.

# Intersection - Returns common elements from both sets
print("Intersection of ", jack_amazon_cart, " and ", jenny_amazon_cart, " is", end=" ")
print(jack_amazon_cart & jenny_amazon_cart)

Output:

Intersection of  {'Smart tv', 'iPod', 'Spectacles', 't-shirt'}  and  {'iPhone', 'Headphones', 'Spectacles', 'frock'}  is {'Spectacles'}

c) Difference

Returns elements that are in set one but not in set two.

# Difference - Returns elements that are in set 1 but not in set2
print("Difference between", jack_amazon_cart, " and ", jenny_amazon_cart, " is", end=" ")
print(jack_amazon_cart - jenny_amazon_cart)

Output:

Difference between {'Smart tv', 'iPod', 'Spectacles', 't-shirt'}  and  {'iPhone', 'Headphones', 'Spectacles', 'frock'}  is {'Smart tv', 't-shirt', 'iPod'}

d) Subset

Returns True if set one is a subset of set two.

# Subset - Return True if first set is subset of second set false otherwise
print("Is", {'iPod', 'Smart tv', 'Spectacles'}, " subset of ", jenny_amazon_cart, " ?", end=" ")
print({'iPod', 'Smart tv', 'Spectacles'} <= jack_amazon_cart)

Output:

Is {'Smart tv', 'Spectacles', 'iPod'}  subset of  {'iPhone', 'Headphones', 'Spectacles', 'frock'}  ? True

e) Superset

Returns True if set one contains all elements of set two.

# Superset - Returns True if the first set contains all elements from second set
print("Is ", {'iPod', 'Smart tv', 'Spectacles'}, " superset of ", jack_amazon_cart, " ?", end=" ")
print({'iPod', 'Smart tv', 'Spectacles'} >= jack_amazon_cart, end="\n\n")
print("Is ", {'iPod', 'Smart tv', 'Spectacles', 't-shirt', 'watch'}, " superset of ", jack_amazon_cart, " ?", end=" ")
print({'iPod', 'Smart tv', 'Spectacles', 't-shirt', 'watch'} >= jack_amazon_cart)

Output:

Is  {'Smart tv', 'Spectacles', 'iPod'}  superset of  {'Smart tv', 'iPod', 'Spectacles', 't-shirt'}  ? False

Is  {'watch', 'iPod', 'Smart tv', 'Spectacles', 't-shirt'}  superset of  {'Smart tv', 'iPod', 'Spectacles', 't-shirt'}  ? True

Set Methods:

We’ll use the below set as an example for all the methods.

code_threads_set = {'c', 'o', 'd', 'e', 't', 'h', 'r', 'e', 'a', 'd', 's'}

Method	Description
add()	add elements to the set. Ex: code_threads_set.add(‘d’)
remove()	removes the element and throws an error if the element does not exist. Ex: code_threads_set.remove(‘d’)
clear()	remove all elements in the set. Ex: code_threads_set.clear()
discard()	removes the element and won’t throw any error if the element does not exist. Ex: code_threads_set.discard(‘f’)
pop()	removes a random element and returns it. Ex: code_threads_set.pop()
copy()	returns the shallow copy of the set. Ex: dup = code_threads_set.copy()
update()	update the set with the given iterable. Ex: code_threads_set.update([‘d’, ‘p’, ‘v’])

Frequently Asked Questions

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