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Python Set union()

The Python set union() method returns a new set with distinct elements from all the sets.

The union of two or more sets is the set of all distinct elements present in all the sets. For example:

A = {1, 2}
B = {2, 3, 4}
C = {5}

Then,
A∪B = B∪A = {1, 2, 3, 4}
A∪C = C∪A = {1, 2, 5}
B∪C = C∪B = {2, 3, 4, 5}

A∪B∪C = {1, 2, 3, 4, 5}
Union of Sets
Union of three set shown in green color

The syntax of union() is:

A.union(*other_sets)

Note: * is not part of the syntax. It is used to indicate that the method can take 0 or more arguments.


Return Value from union()

  • The union() method returns a new set with elements from the set and all other sets (passed as an argument).
  • If the argument is not passed to union(), it returns a shallow copy of the set.

Example 1: Working of union()

A = {'a', 'c', 'd'}
B = {'c', 'd', 2 }
C = {1, 2, 3}

print('A U B =', A.union(B))
print('B U C =', B.union(C))
print('A U B U C =', A.union(B, C))
print('A.union() =', A.union())

Output

A U B = {2, 'a', 'd', 'c'}
B U C = {1, 2, 3, 'd', 'c'}
A U B U C = {1, 2, 3, 'a', 'd', 'c'}
A.union() = {'a', 'd', 'c'}

You can also find the union of sets using the | operator.

Example 2: Set Union Using the | Operator

A = {'a', 'c', 'd'}
B = {'c', 'd', 2 }
C = {1, 2, 3}

print('A U B =', A| B)
print('B U C =', B | C)
print('A U B U C =', A | B | C)

Output

A U B = {2, 'a', 'c', 'd'}
B U C = {1, 2, 3, 'c', 'd'}
A U B U C = {1, 2, 3, 'a', 'c', 'd'}