frozenset() in Python

Python Method creates an immutable Set object from an iterable. It is a built-in Python function. As it is a set object, therefore, we cannot have duplicate values in the frozenset.

Example

In this example, we are creating a frozen set with the list in Python.

animals = frozenset(["cat", "dog", "lion"])
print("cat" in animals) 
print("elephant" in animals)  

Output

True
False

Python frozenset() Syntax 

Syntax : frozenset(iterable_object_name)
Parameter : iterable_object_name

• This function accepts iterable object as input parameter.

Return :  Returns an equivalent frozenset object.

frozenset() in Python Examples

Working of Python frozenset()

In this example, we are showing how to create a frozen set in Python and we are showing that frozen set objects are immutable and can not be modified after the creation.

fruits = frozenset(["apple", "banana", "orange"])
print(fruits) 
fruits.add("cherry")
print(fruits) 

Output

frozenset({'orange', 'apple', 'banana'})
ERROR!
Traceback (most recent call last):
  File "<main.py>", line 3, in <module>
AttributeError: 'frozenset' object has no attribute 'add'

Python frozenset for Tuple

If no parameters are passed to frozenset() function, then it returns an empty frozenset type object in Python.  

# passing an empty tuple
nu = ()

# converting tuple to frozenset
fnum = frozenset(nu)

# printing empty frozenset object
print("frozenset Object is : ", fnum)

Output

frozenset Object is :  frozenset()

Python frozenset for List

Here as a parameter a list is passed and now its frozen set object is returned.

l = ["Geeks", "for", "Geeks"]
 
# converting list to frozenset
fnum = frozenset(l)
 
# printing empty frozenset object
print("frozenset Object is : ", fnum)

Output 

frozenset Object is :  frozenset({'Geeks', 'for'})

frozenset in Python for Dictionary

Since frozen set objects are immutable, they are mainly used as keys in dictionary or elements of other sets. The below example explains it clearly. 

# creating a dictionary 
Student = {"name": "Ankit", "age": 21, "sex": "Male", 
           "college": "MNNIT Allahabad", "address": "Allahabad"}

# making keys of dictionary as frozenset
key = frozenset(Student)

# printing dict keys as frozenset
print('The frozen set is:', key)

Output

The frozen set is: frozenset({'address', 'name', 'age', 'sex', 'college'})

Exceptions while using the frozenset() method in Python

If by mistake we want to change the frozen set object, then it throws a TypeError

# creating a list 
favourite_subject = ["OS", "DBMS", "Algo"]

# creating a frozenset
f_subject = frozenset(favourite_subject)

# below line will generate error
f_subject[1] = "Networking"

Output 

TypeError                                 Traceback (most recent call last)
Input In [13], in <cell line: 8>()
      5 f_subject = frozenset(favourite_subject)
      7 # below line will generate error
----> 8 f_subject[1] = "Networking"
TypeError: 'frozenset' object does not support item assignment

Frozenset operations

Frozen sets are immutable sets that allow you to perform various set operations such as union, intersection, difference, and symmetric difference.

# initialize A and B
A = frozenset([1, 2, 3, 4])
B = frozenset([3, 4, 5, 6])

# copying a frozenset
C = A.copy()
print(C)  

# union
union_set = A.union(B)
print(union_set) 

# intersection
intersection_set = A.intersection(B)
print(intersection_set)  

difference_set = A.difference(B)
print(difference_set) 

# symmetric_difference
symmetric_difference_set = A.symmetric_difference(B)
print(symmetric_difference_set)  

Output 

frozenset({1, 2, 3, 4})
frozenset({1, 2, 3, 4, 5, 6})
frozenset({3, 4})
frozenset({1, 2})
frozenset({1, 2, 5, 6})