Python Set difference_update :
In this tutorial, we will learn about the difference_update method of python set.
Definition of difference_update :
The difference between two set SetA and SetB is a new set that holds only the elements of SetA and not of SetB. SetA - SetB is used to indicate the difference.
For two set SetA and SetB, the difference_update method will convert SetA to SetA - SetB. In other words, this method is an alternative way to find out the difference between the two sets.
Syntax of difference_update :
The syntax is as below :
SetA.difference_update(SetB)
SetA and SetB are two different sets. This method call will update the SetA values with SetA - SetB. It will return None. Only the value of SetA will change.
SetB will remain unchanged.
Example Program :
#1
setA = set()
setB = set()
#2
setA_length = int(input(“Enter the size of the first set : “))
setB_length = int(input(“Enter the size of the second set : “))
#3
print(“\n”)
print(“Enter values for the first set one by one : \n”)
for i in range(setA_length):
e = int(input(“Enter value {} : “.format(i+1)))
setA.add(e)
#4
print(“\n”)
print(“Enter values for the second set one by one : \n”)
for i in range(setB_length):
e = int(input(“Enter value {} : “.format(i+1)))
setB.add(e)
#5
print(“\nBefore : “)
print(“SetA : {} “.format(setA))
print(“SetB : {} “.format(setB))
#6
setA.difference_update(setB)
#7
print(“\nAfter : “)
print(“SetA : {} “.format(setA))
print(“SetB : {} “.format(setB))
Explanation :
The commented numbers in the above program denote the step numbers below :
-
Create two empty set setA and setB.
-
Ask the user to enter the size of the first and the second set. Read the values and store them in setA_length and setB_length variables.
-
Read the inputs for the first set one by one using one for loop.
-
Similarly, read the inputs for the second set one by one using one for loop.
-
Print values of both set to the user.
-
Call difference_update method on setA and setB.
-
Print values of both set to the user again after the difference_update method call.
Sample Output :
Enter the size of the first set : 3
Enter the size of the second set : 2
Enter values for the first set one by one :
Enter value 1 : 1
Enter value 2 : 2
Enter value 3 : 3
Enter values for the second set one by one :
Enter value 1 : 1
Enter value 2 : 2
Before :
SetA : {1, 2, 3}
$ python3 example.py
Enter the size of the first set : 3
Enter the size of the second set : 2
Enter values for the first set one by one :
Enter value 1 : 1
Enter value 2 : 2
Enter value 3 : 3
Enter values for the second set one by one :
Enter value 1 : 1
Enter value 2 : 2
Before :
SetA : {1, 2, 3}
SetB : {1, 2}
After :
SetA : {3}
SetB : {1, 2}
Conclusion :
difference_update method comes in handy if you want to find out the difference between two sets and the original sets are not required later. Instead of creating a new variable and place the new values in it, we can use difference_update and put the difference elements in the first set. Try to run the example shown above and drop one comment below if you have any queries.