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How to join two or more sets in Python

Saad Akbar

Overview

Sets can be joined in Python in a number of different ways. For instance, update() adds all the elements of one set to the other. Similarly, union() combines all the elements of the two sets and returns them in a new set. Both union() and update() operations exclude duplicate elements.

Example for union()

set1 = {1, 2 , 3}
set2 = {4, 5, 6}

set_union = set1.union(set2)
print(set_union)

Explanation

Lines 1–5: The union operation returns a new set, set_union, containing all the items from the previous 2 sets, set1, set2.

Example for update()

set1 = {1, 2 , 3}
set2 = {4, 5, 6}

set1.update(set2)
print(set1)

Explanation

Lines 1–5: The update method adds the values of set2 into set1.

The intersection_update() and intersection() methods

There are also some methods that keep only duplicates. These are intersection_update() and intersection().

The intersection_update() method only stores the items that are present in both sets. While the intersection() method returns a new set containing items that are present in both sets.

Example for intersection_update()

set1 = {"apple", "mango", "cherry"}
set2 = {"strawberry", "mango", "apple"}

set1.intersection_update(set2)

print(set1)

Explanation

Lines 1–6: The intersection_update() only keeps those items in set1 that are present in both sets.

Example for intersection()

set1 = {"apple", "mango", "cherry"}
set2 = {"strawberry", "mango", "apple"}

set3 = set1.intersection(set2)

print(set3)

Explanation

Lines 1–6: The intersection() method returns a new set, set3, that contains values that are present in both the previous sets.

The symmetric_difference_update() and symmetric_difference() method

Another way of joining sets is by keeping all the elements except duplicates. For this operation we use symmetric_difference_update() and symmetric_difference() method.

The symmetric_difference_update() method stores only the elements that are not present in both sets. While symmetric_difference() stores only the elements that are not present in both sets in the new set and returns it.

Example for symmetric_difference_update()

set1 = {"apple", "mango", "cherry"}
set2 = {"strawberry", "mango", "apple"}

set1.symmetric_difference_update(set2)

print(set1)

Explanation

Lines 1–6: We use symmetric_difference_update() to store those values in set1 that are not present in both sets.

Example for symmetric_difference()

set1 = {"apple", "mango", "cherry"}
set2 = {"strawberry", "mango", "apple"}

set3 = set1.symmetric_difference(set2)

print(set3)

Explanation

Lines 1–6: We use symmetric_difference() to return a new set set3 that only stores those values that are not present in the previous 2 sets.

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