Python issubset
Summary: in this tutorial, you’ll learn about how to use the Python issubset() method to check if a set is a subset of another set.
Introduction to the Python issubset() method
Suppose that you have two sets A and B. Set A is a subset of set B if all elements of A are also elements of B. Then, set B is a superset of set A.
The following Venn diagram illustrates that the set A is a subset of the set B:
Set A and set B can be equal. If set A and set B are not equal, A is a proper subset of B.
In Python, you can use the Set issubset() method to check if a set is a subset of another:
set_a.issubset(set_b)Code language: CSS (css)
If the set_a is a subset of the set_b, the issubset() method returns True. Otherwise, it returns False.
The following example uses the issubset() method to check if the set_a is a subset of the set_b:
numbers = {1, 2, 3, 4, 5}
scores = {1, 2, 3}print(scores.issubset(numbers))
Code language: PHP (php)
Output:
TrueCode language: PHP (php)
By definition, a set is also a subset of itself. The following example returns True:
numbers = {1, 2, 3, 4, 5}print(numbers.issubset(numbers))
Code language: PHP (php)
Output:
TrueCode language: PHP (php)
The following example returns False because some elements in the numbers set aren’t in the scores set. In other words, the numbers set is not a subset of the scores set:
numbers = {1, 2, 3, 4, 5}
scores = {1, 2, 3}print(numbers.issubset(scores))
Code language: PHP (php)
Output:
FalseCode language: PHP (php)
Using subset operators
Besides using the issubset() method, you can use the subset operator (<=) to check if a set is a subset of another set:
set_a <= set_b
The subset operator (<=) returns True if set_a is a subset of the set_b. Otherwise, it returns False. For example:
numbers = {1, 2, 3, 4, 5}
scores = {1, 2, 3}result = scores <= numbers
print(result) # True
result = numbers <= numbers
print(result) # True
Code language: PHP (php)
The proper subset operator (<) check if the set_a is a proper subset of the set_b:
set_a < set_b
For example:
numbers = {1, 2, 3, 4, 5}
scores = {1, 2, 3}result = scores < numbers
print(result) # True
result = numbers < numbers
print(result) # False
Code language: PHP (php)
In this example, the set numbers is not a proper subset of itself, therefore, the < operator returns False.
Summary
- Set A is a subset of set B if all elements of the set A are also elements of the set B
- Use Set
issubset()method returnsTrueif a set is a subset of another set. - Also, use the subset operator (<=) or the proper subset operator (<) to check if a set is a subset or proper subset of another set.