Python Set Difference: The Complete Guide

Python set supports four great operations:

1. Intersection: Elements two sets have in common.
2. Union: All the elements from both sets.
3. Difference: Elements are present on one set but not on the other.
4. Symmetric Difference: Elements from both sets that are not present on the other.

Consider the following image for better understanding.

Here, A contains {a,b,c,d,e} and B contains {a,e,f,g} . So A-B={b,c,d} and B-A={f,g} .

Python Set Difference

Python set difference() is a built-in function that helps us find the difference between two sets. It works like a math intersection (A∩B). This means that if A and B are two sets, then their difference will be: 

A-B = A-(A∩B)

B-A = B-(A∩B)

The difference() method returns the set difference of two sets. If A and B are two sets. The set difference between A and B is a set of elements that exist only in set A but not in B.

Syntax

First_Set.difference(Second_Set)

The above syntax will help us to find the difference between First_Set-Second_Set.

So, If we want to find A-B, the syntax will be the following.

A.difference(B)

Return Value

The difference() function returns the difference of two given set without changing the original sets. This means it returns a new set.

Programming Example

See the following code example.

# app.py

# Declaring two sets
A = {'a', 'b', 'c', 'd', 'e'}
B = {'a', 'e', 'f', 'g'}

# Now we will apply difference() to find

# A-B
print("Difference between A-B is: ", A.difference(B))
# B-A
print("Difference between B-A is: ", B.difference(A))

Output

Difference between A-B is:  {'c', 'b', 'd'}
Difference between B-A is:  {'g', 'f'}

Here in this example, we have declared two sets, A and B, and then we have used the difference() method to find the difference between the two sets.

Using the minus (-) operator

See the following code.

# app.py

# Declaring two sets
A = {'a', 'b', 'c', 'd', 'e'}
B = {'a', 'e', 'f', 'g'}

# Now we will apply the minus operator to find

# A-B
print("Difference between A-B is: ", A-B)
# B-A
print("Difference between B-A is: ", B-A)

Output

Difference between A-B is:  {'d', 'c', 'b'}
Difference between B-A is:  {'g', 'f'}

Here in this example, we have declared two sets, A and B, and then we have used the minus operator (-) to find the difference between the two sets.

The original sets are not changed; it remains unchanged.

The difference between the two sets in Python equals the difference between the number of elements in the two sets.

That’s it for this tutorial.

See also

Python set add()

Python set clear()

Python set copy()