Union() Function in Set Python

Last Updated : 18 Apr, 2026

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.

setUnion
Union of two sets

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

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

Output
{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.

Python 
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))

Output
{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.

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

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

Output
{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.

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

Output
{'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.
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