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)

Try it

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)

Try it

Output:

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

The union() method vs. set union operator #

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)

Try it

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

Try it

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.

Quiz #