In this tutorial, we will look at how to check whether a set in Python is a subset of another set with the help of some examples.
What is a subset?
Let’s say we have two sets, A and B. Now, if all the elements of set A are present in set B then A is said to be a subset of B. Here’s an example –

You can see that all the elements of set A are present in set B, thus, we can say that set A is a subset of set B. However, the converse is not true, B is not a subset of A since there are elements in B that are not in A.
Check if a set is a subset of another set in Python
The Python set data structure comes with a number of built-in functions to accomplish common set operations like union, intersection, difference, etc. You can use the Python set issubset()
function to check whether a set is a subset of another set. The following is the syntax:
# check if a is a subset of b a.issubset(b)
We call the issubset()
function from set a and pass the set b as an argument to check whether set a is a subset of set b. It returns a boolean value. Let’s look at an example.
# create two sets a = {1, 2, 3} b = {1, 2, 3, 4} # check if a is subset of b a.issubset(b)
Output:
True
We get True
as the output since a is in fact, a subset of set b.
Let’s look at another example.
# create two sets a = {1, 2, 3} b = {1, 3, 4, 5} # check if a is subset of b a.issubset(b)
Output:
False
Here we get False
as the output because not all elements of set a are present in set b (2 from set a is not present in b). Thus, set a is not a subset of set b.
Alternatively, you can use the <=
operator to check if a set is a subset of another set. For example,
# create two sets a = {1, 2, 3} b = {1, 2, 3, 4} # check if a is subset of b a <= b
Output:
True
We get the same result as we did with the set issubset()
function.
Special Cases
There are also some special cases to keep in mind when checking for subsets.
- Every set is a subset of itself.
# create a set a = {1, 2, 3} # check if a is subset of itself a.issubset(a)
Output:
True
- Empty set is subset of every set.
# create a set a = set() b = {1, 2, 3} # check if a is subset of b a.issubset(b)
Output:
True
You might also be interested in –
- Python – Get Union of Two or more Sets
- Python – Intersection of two or more Sets
- Set Difference in Python – With Examples
Subscribe to our newsletter for more informative guides and tutorials.
We do not spam and you can opt out any time.