Python Set Union

Summary: in this tutorial, you’ll learn how to union two or more sets by using the Python set union() or set union operator (|).

Introduction to the set union

The union of two sets returns a new set that contains distinct elements from both sets.

Suppose that you have the following sets:

s1 = {'Python', 'Java'}
s2 = {'C#', 'Java'}Code language: JavaScript (javascript)

The union of the s1 and s2 sets returns the following set:

{'Java','Python', 'C#'}Code language: JavaScript (javascript)

Typically, you use the Venn diagram to illustrate the union of two sets. For example:

Union sets using union() method

In Python, to union two or more sets, you use the union() method:

new_set = set.union(another_set, ...)Code language: JavaScript (javascript)

The following example shows how to union the s1 and s2 sets:

s1 = {'Python', 'Java'}
s2 = {'C#', 'Java'}

s = s1.union(s2)

print(s)Code language: PHP (php)

Output:

{'Python', 'Java', 'C#'}
Code language: JavaScript (javascript)

Union sets using the | operator

Python provides you with the set union operator | that allows you to union two sets:

new_set = set1 | set2

The set union operator (|) returns a new set that consists of distinct elements from both set1 and set2.

The following example shows how to use the union operator (|) to union the s1 and s2 sets:

s1 = {'Python', 'Java'}
s2 = {'C#', 'Java'}

s = s1 | s2

print(s)Code language: PHP (php)

Output:

{'Java', 'C#', 'Python'}
Code language: JavaScript (javascript)

The union() method vs. set union operator

In fact, the union() method accepts one or more iterables, converts the iterables to sets, and performs the union.

The following example shows how to pass a list to the union() method:

rates = {1, 2, 3}
ranks = [2, 3, 4]

ratings = rates.union(ranks)

print(ratings)Code language: PHP (php)

Output:

{1, 2, 3, 4}

However, the union operator (|) only allows sets, not iterables like the union() method.

The following example causes an error:

rates = {1, 2, 3}
ranks = [2, 3, 4]

ratings = rates | ranks

Error:

TypeError: unsupported operand type(s) for |: 'set' and 'list'Code language: JavaScript (javascript)

In conclusion, the union() method accepts the iterables while the union operator only allows sets.

Summary

• The union of two or more sets returns distinct values from both sets.
• Use union() method or set union operator (|) to union two or more sets.
• The union() method accepts one or more iterables while the set union operator (|) only accepts sets.