Python Set difference_update()

February 2, 2021

Difference_update() in Python Sets

 

This method helps to find out the difference between two sets.

The difference_update() method is same as the difference() method in Python sets. The only difference is that difference() method returns a new set whereas difference_update() method updates the calling set.

Python Set difference_update()
Let us understand this with an example:
  • set A = { 1, 2, 3, 4, 5 }
  • set B = { 1, 3, 5, 7 }

For A – B

  • A.difference(B)               : It will return a new set having i.e. newSet = { 2, 4 }
  • A.difference_update(B) : It will update the set A with A-B i.e. set A = { 2, 4 }

For B – A

  • B.difference(A)               : It will return a new set having i.e. newSet = { 7 }
  • B.difference_update(A) : It will update the set B with B-A i.e.  set B = { 7 }

Syntax :


set1.difference_update(set2)

Return Type :

  • difference_update() method does not return any value. So it returns None.
  • It only changes the values of existing set.

#difference of sets using difference_update() method

#  A – B will be updates in set A
A = { 1, 2, 3, 4, 5, 6 }
B = { 2, 4, 6, 8, 10 }
print( A.difference_update(B) )   #returns NONE
print(A)    # set A is updated
print(B)    # set B remained same

#  B – A will be updates in set B
A = { 1, 2, 3, 4, 5, 6 }
B = { 2, 4, 6, 8, 10 }
print( B.difference_update(A) )   #returns NONE
print(A)    # set A remained same
print(B)    # set B is updated


 Output :

 None
 {1, 3, 5}
 {2, 4, 6, 8, 10}

 None
 {1, 2, 3, 4, 5, 6}
 {8, 10}