The set.union() method in Python returns a new set containing all unique elements from two or more sets. It combines the given sets and automatically removes duplicate values. The original sets remain unchanged.

Example: In this example, two sets a and b are combined using union().

a = {1, 2, 3}
b = {3, 4, 5}
print(a.union(b))

{1, 2, 3, 4, 5}

Explanation: a.union(b) merges both sets. Duplicate element 3 appears only once.

Syntax

set1.union(set2, set3, ...)

• Parameters: One or more sets to be merged. If no argument is given, it returns a copy of the original set.
• Returns: Returns a new set containing all unique elements.

Examples

Example 1: In this example, union on three sets is performed using multiple union() calls and by passing multiple sets directly.

a = {2, 4, 5, 6}
b = {4, 6, 7, 8}
c = {7, 8, 9, 10}

print(a.union(b).union(c))
print(a.union(b, c))

{2, 4, 5, 6, 7, 8, 9, 10}
{2, 4, 5, 6, 7, 8, 9, 10}

Explanation: a.union(b).union(c) merges sets step by step and a.union(b, c) merges all sets at once.

Example 2: Here, | operator is used as a shortcut for union operation on sets.

a = {2, 4, 5, 6}
b = {4, 6, 7, 8}
c = {7, 8, 9, 10}

print(a | b)
print(a | b | c)

{2, 4, 5, 6, 7, 8}
{2, 4, 5, 6, 7, 8, 9, 10}

Explanation:

• a | b performs union of two sets.
• a | b | c merges all three sets.
• The | operator works the same as union().

Example 3: In this example, union() is applied on sets of strings.

a = {'ab', 'ba', 'cd', 'dz'}
b = {'cd', 'ab', 'dd', 'za'}
print(a.union(b))

{'cd', 'za', 'ba', 'ab', 'dd', 'dz'}

Explanation:

• a.union(b) combines both sets.
• Common elements 'ab' and 'cd' appear only once.
• The result contains all unique strings.