Python Set issubset() method returns True if all items of a set are present in another set (passed as an argument). If not, then it returns False. Lets, assume A={1,2,4} and B={1,2,3,4,5} are two sets. So we can see the following figure.
Python Set issubset()
Python Set issubset() is a built-in function that is used to find whether a set is a subset of another set or not. If all the elements of one set are present in another set, then the first set is called a subset of the second set. This means the second set must contain values that are present in the first set.
Set A is said to be the subset of Set B if all items of A are in B. Here, Set A is a subset of B.
Syntax
First_Set.issubset(Second_Set)
Here, this syntax will check if First_Set is a subset of Second_Set or not.
Return Value
The function returns two types of values-
True: If First_Set is a subset of Second_Set
False: If First_Set is not a subset of Second_Set
Example
See the following code.
# app.py
# Declaring two sets
# Even nums between 2 and 10
set1 = {2, 4, 6, 8, 10}
# Multiple of 4 from 4 to 10
set2 = {4, 8}
# Multiple of 4 from 4 to 20
set3 = {4, 8, 12, 16, 20}
# priting both the sets
print("Set1 is: ", set1)
print("Set2 is : ", set2)
print("Set3 is: ", set3)
# Now we will find if they are disjoint
print("Is Set2 Subset of Set1? ", set2.issubset(set1))
print("Is Set3 Subset of Set1? ", set3.issubset(set1))
Output
Set1 is: {2, 4, 6, 8, 10}
Set2 is : {8, 4}
Set3 is: {4, 8, 12, 16, 20}
Is Set2 Subset of Set1? True
Is Set3 Subset of Set1? False
In this program, we have declared three sets, Set1, which is even numbers from 1 to 10, Set2, which contains a multiple of 4 from 4 to 10, and Set3, which includes a multiple of 4 from 4 to 20.
Now, we are finding if Set2 is a subset of Set1 or not. So, we can see that all the elements of Set2 are present in Set1. So, Set2 is a subset of Set1.
On the other hand, we can see that not all the elements are present in Set1 of Set3, so it is not a subset of Set1. That’s why the return value is False.
See the following second example.
# app.py
A = {11, 21, 19}
B = {11, 21, 19, 46, 18}
C = {11, 21, 46, 18}
# Returns True
print(A.issubset(B))
# Returns False
# B is not subset of A
print(B.issubset(A))
# Returns False
print(A.issubset(C))
# Returns True
print(C.issubset(B))
Output
python3 app.py True False False True
That’s it for this tutorial.
See also
Python set intersection_update()
