issubset() function in Python

In this article, we will learn the implementation and usage of issubset() function available in the Python Standard Library.

The issubset() method returns boolean True when all elements of a set are present in another set (passed as an argument) otherwise, it returns boolean False.

In the figure given below B is a subset of A. When A & B are identical sets, A is considered a proper subset of B, meaning both sets contain the same elements.

Syntax

<set1>.issubset(<set2>)

Return Value

boolean True/False

Example

Let's look at a basic example to understand the concept ?

A = {'t', 'u', 'o', 'r', 'i', 'a', 'l'}
B = {'t', 'u'}
C = {'p', 'o', 'i', 'n', 't'}

print("B.issubset(A):", B.issubset(A))
print("C.issubset(A):", C.issubset(A))
print("B.issubset(C):", B.issubset(C))

B.issubset(A): True
C.issubset(A): False
B.issubset(C): False

Explanation

Here, all elements of B ('t', 'u') are contained in A, so B.issubset(A) returns True. Set C contains elements like 'p' and 'n' that are not in A, so C.issubset(A) returns False.

Using Different Iterable Types

The issubset() method can accept other iterable types like lists, tuples, and strings as arguments ?

# Set to compare against
numbers = {1, 2, 3, 4, 5}

# Different iterable types
subset_list = [1, 2, 3]
subset_tuple = (1, 2)
subset_string = "12"

print("List subset:", numbers.issuperset(subset_list))
print("Tuple subset:", numbers.issuperset(subset_tuple))

# Using issubset with different types
small_set = {1, 2}
print("Set subset of list:", small_set.issubset([1, 2, 3, 4]))
print("Set subset of tuple:", small_set.issubset((1, 2, 3)))

List subset: True
Tuple subset: True
Set subset of list: True
Set subset of tuple: True

Explanation

Python automatically converts the iterable arguments (lists, tuples) to sets for comparison. The calling object must always be a set, but the argument can be any iterable type.

Proper Subset vs Subset

Two identical sets are considered subsets of each other ?

set1 = {1, 2, 3}
set2 = {1, 2, 3}
set3 = {1, 2}

print("Identical sets - set1.issubset(set2):", set1.issubset(set2))
print("Identical sets - set2.issubset(set1):", set2.issubset(set1))
print("Proper subset - set3.issubset(set1):", set3.issubset(set1))

Identical sets - set1.issubset(set2): True
Identical sets - set2.issubset(set1): True
Proper subset - set3.issubset(set1): True

Comparison Table

Conclusion

The issubset() method is useful for checking if all elements of one set exist in another set. It accepts various iterable types as arguments and returns True for identical sets, making it versatile for set comparison operations.