Python frozenset()

Frozen set is just an immutable version of a Python set object. While elements of a set can be modified at any time, elements of the frozen set remain the same after creation.

Due to this, frozen sets can be used as keys in Dictionary or as elements of another set. But like sets, it is not ordered (the elements can be set at any index).

The syntax of frozenset() function is:

frozenset([iterable])

frozenset() Parameters

The frozenset() function takes a single parameter:

• iterable (Optional) - the iterable which contains elements to initialize the frozenset with.
  Iterable can be set, dictionary, tuple, etc.

Return value from frozenset()

The frozenset() function returns an immutable frozenset initialized with elements from the given iterable.

If no parameters are passed, it returns an empty frozenset.

Example 1: Working of Python frozenset()

# tuple of vowels
vowels = ('a', 'e', 'i', 'o', 'u')

fSet = frozenset(vowels)
print('The frozen set is:', fSet)
print('The empty frozen set is:', frozenset())

# frozensets are immutable
fSet.add('v')

Output

The frozen set is: frozenset({'a', 'o', 'u', 'i', 'e'})
The empty frozen set is: frozenset()
Traceback (most recent call last):
  File "<string>, line 8, in <module>
    fSet.add('v')
AttributeError: 'frozenset' object has no attribute 'add'

Example 2: frozenset() for Dictionary

When you use a dictionary as an iterable for a frozen set, it only takes keys of the dictionary to create the set.

# random dictionary
person = {"name": "John", "age": 23, "sex": "male"}

fSet = frozenset(person)
print('The frozen set is:', fSet)

Output

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

Frozenset operations

Like normal sets, frozenset can also perform different operations like copy, difference, intersection, symmetric_difference, and union.

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

# copying a frozenset
C = A.copy()  # Output: frozenset({1, 2, 3, 4})
print(C)

# union
print(A.union(B))  # Output: frozenset({1, 2, 3, 4, 5, 6})

# intersection
print(A.intersection(B))  # Output: frozenset({3, 4})

# difference
print(A.difference(B))  # Output: frozenset({1, 2})

# symmetric_difference
print(A.symmetric_difference(B))  # Output: frozenset({1, 2, 5, 6})

Output

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

Similarly, other set methods like isdisjoint, issubset, and issuperset are also available.

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

# isdisjoint() method
print(A.isdisjoint(C))  # Output: True

# issubset() method
print(C.issubset(B))  # Output: True

# issuperset() method
print(B.issuperset(C))  # Output: True

Output

True
True
True