How to Find Union of Two Sets in Python Quickly

To find the union of two sets in Python, use the union() method or the | operator. Both combine all unique elements from both sets into a new set.

Syntax

The union of two sets can be found using either the union() method or the | operator.

• set1.union(set2): Returns a new set with all unique elements from set1 and set2.
• set1 | set2: Another way to get the union using the pipe operator.

python

union_set = set1.union(set2)
# or
union_set = set1 | set2

Example

This example shows how to find the union of two sets using both the union() method and the | operator.

python

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

# Using union() method
union1 = set1.union(set2)

# Using | operator
union2 = set1 | set2

print("Union using union():", union1)
print("Union using | operator:", union2)

Output

Union using union(): {1, 2, 3, 4, 5}
Union using | operator: {1, 2, 3, 4, 5}

Common Pitfalls

Some common mistakes when finding the union of sets include:

• Using + operator which does not work with sets.
• Modifying one of the original sets unintentionally instead of creating a new set.
• Confusing union with intersection which finds common elements.

python

wrong_union = set1 + set2  # This will cause an error

# Correct way:
correct_union = set1.union(set2)

Quick Reference

Operation	Syntax	Description
Union using method	set1.union(set2)	Returns a new set with all unique elements from both sets
Union using operator	set1 | set2	Returns a new set with all unique elements from both sets
In-place union	set1.update(set2)	Adds elements from set2 into set1 (modifies set1)

Key Takeaways

Use union() or | to find the union of two sets in Python.

The union operation returns a new set with all unique elements from both sets.

Avoid using + operator with sets as it causes errors.

Use update() if you want to add elements to an existing set instead of creating a new one.

Union is different from intersection; union combines all elements, intersection finds common ones.