frozenset

The built-in frozenset data type is similar to a set, but it is immutable. This means once a frozenset is created, its elements cannot be changed, added, or removed.

Frozensets are useful when you need a set that should remain constant throughout the program’s execution:

Python 
>>> frozenset(['apple', 'banana', 'cherry'])
frozenset({'apple', 'banana', 'cherry'})

frozenset Constructor

Python Syntax 
frozenset([iterable])

Arguments

Argument Description Default Value
iterable An iterable object whose elements will populate the frozenset set()

Return Value

  • Returns a Python frozenset object

frozenset Examples

Creating an empty frozenset by calling frozenset() with no arguments:

Python 
>>> empty_fs = frozenset()
>>> empty_fs
frozenset()

Creating a frozenset using a list as an argument:

Python 
>>> frozenset(["apple", "banana", "cherry"])
frozenset({'apple', 'banana', 'cherry'})

frozenset Methods

Method Description
.copy() Returns a shallow copy of the frozenset.
.difference(other) Returns a new frozenset with elements in self but not in other.
.intersection(other) Returns a new frozenset with elements common to self and other.
.isdisjoint(other) Returns True if self and other have no elements in common.
.issubset(other) Returns True if all elements of self are in other.
.issuperset(other) Returns True if all elements of other are in self.
.symmetric_difference(other) Returns a new frozenset with elements in either self or other but not both.
.union(other) Returns a new frozenset with elements from both self and other.

frozenset Common Use Cases

The most common use cases for the frozenset include:

  • Using as keys in a dictionary
  • Storing sets of data that should not be changed
  • Performing set operations without modifying the original set

frozenset Real-World Example

Say that you need to define an immutable set of constants to represent valid colors in a drawing app:

Python 
>>> VALID_COLORS = frozenset(["red", "green", "blue"])
>>> "red" in VALID_COLORS
True
>>> "purple" in VALID_COLORS
False

In this example, you define the VALID_COLORS constant using a frozenset. Then, you use the constant in membership tests because sets are quite efficient for this type of operation.

Sets in Python

Tutorial

Sets in Python

In this tutorial you'll learn how to work effectively with Python's set data type. You'll see how to define set objects in Python and discover the operations that they support and by the end of the tutorial you'll have a good feel for when a set is an appropriate choice in your own programs.

basics python

For additional information on related topics, take a look at the following resources:

By Leodanis Pozo Ramos • Updated Dec. 6, 2024 • Reviewed by Dan Bader
Python’s Built-in Data Types Share Feedback