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Python frozenset() – Every You Need To Know

What Is Frozenset() In Python

Hey there! So today we are here to discuss the Python frozenset() method.

So before we get into the method, let us know what a frozenset is.

What is a frozenset?

A frozenset is an unordered, un-indexed, and immutable collection of elements. It provides all the functionalities that a set offers in Python, the only difference being the fact that a frozenset is immutable, i.e. can’t be changed after it is created.

Hence in simple words, frozen sets are immutable sets.

The Python frozenset() Method

The Python frozenset() method returns a new frozenset object whose elements are taken from the passed iterable. If iterable is not specified, a new empty set is returned.

Note: The elements must be hashable.

fz = frozenset([iterable])

When nothing is specified, the frozenset() method returns an empty frozenset object to fz.

To get a better understanding of how the method works, let us look at an example.

# List Initialisation
list1 = [0, 1, 2, 3, 4, 5, 6]

fz = frozenset(list1)
print(fz)

fz = frozenset()  # empty frozenset
print(fz)

print("Type of fz: ", type(fz))

Output:

frozenset({0, 1, 2, 3, 4, 5, 6})
frozenset()
Type of fz:  <class 'frozenset'>

Here, firstly we have initialized a list(list1) and then passed it as iterable to the frozenset() method. In return we get a frozenset object(fz) with elements from the list. When nothing is passed, fz is now an empty frozenset object.

Frozenset Initialization

In the below-given example, we have initialized a frozenset using the Python frozenset() method by passing different iterables like list, tuple, set, and dictionary.

# Initialisation
list1 = [1, 2, 3, 4, 5]

fz = frozenset(list1)  # from list object
print(fz)

fz = frozenset([1, 2, 3, 4, 5])  # from list
print(fz)

fz = frozenset({5: 'a', 4: 'B', 3: 'C', 2: 'D', 1: 'E', 0: '0'})# from dict
print(fz)

fz = frozenset({'Python', 'Java', 'C', 'C++', 'Kotlin', 'R'})# from set
print(fz)

fz = frozenset((17, 55, 26, 90, 75, 34)) # from tuple
print(fz)

Output:

frozenset({1, 2, 3, 4, 5})
frozenset({1, 2, 3, 4, 5})
frozenset({0, 1, 2, 3, 4, 5})
frozenset({'Java', 'Kotlin', 'Python', 'C', 'R', 'C++'})
frozenset({34, 90, 75, 17, 55, 26})

For each case, we get a frozenset object with the corresponding iterable elements in it. But carefully note, that in the case of a dictionary only the keys are being considered.

Operations on a Python frozenset

We can get names of all the methods related to a frozenset object using the dir() method.

fo = frozenset([1, 2, 3, 4, 5])

print(dir(fo))

Output:

['__and__', '__class__', '__contains__', '__delattr__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__iter__', '__le__', '__len__', '__lt__', '__ne__', '__new__', '__or__', '__rand__', '__reduce__', '__reduce_ex__', '__repr__', '__ror__', '__rsub__', '__rxor__', '__setattr__', '__sizeof__', '__str__', '__sub__', '__subclasshook__', '__xor__', 'copy', 'difference', 'intersection', 'isdisjoint', 'issubset', 'issuperset', 'symmetric_difference', 'union']

Notice from the above output, that various functions like add(), remove(), update(), pop() etc.(used to change/update elements, available for sets) are missing. Again this is due to the fact that a frozen set is immutable.

So now let us look at the available methods for frozen sets, using which we can perform various operations.

fs = frozenset([1, 12, 23, 45, 67, 89, 100])

print("Given Frozenset =", fs)

fs_len = len(fs)
print("Length of Frozenset =", fs_len)

print("23 in fs? ", 23 in fs)

print("23 not in fs? ", 23 not in fs)

print("Sets are disjoint? ", fs.isdisjoint(frozenset([10, 5])))

print("Set is Subset? ", fs.issubset(set([1, 2, 3, 4, 12, 23, 45, 67, 89, 100])))

print("fs is superset? ", fs.issuperset(frozenset({1, 100})))

print("Union of sets: ", fs.union(frozenset([-1, -12])))

print("Intersection: ", fs.intersection(set([1, 10, 100])))

print("Difference: ", fs.difference(frozenset([1, 10, 100])))

print("Symmetric difference: ", fs.symmetric_difference(frozenset([1, 10, 100])))

fs_copy = fs.copy()
print("Copy of fs: ", fs_copy)

Output:

Given Frozenset = frozenset({1, 67, 100, 12, 45, 23, 89})
Length of Frozenset = 7
23 in fs?  True
23 not in fs?  False
Sets are disjoint?  True
Set is Subset?  True
fs is superset?  True
Union of sets:  frozenset({1, 67, 100, 12, 45, -12, 23, 89, -1})
Intersection:  frozenset({1, 100})
Difference:  frozenset({67, 12, 45, 23, 89})
Symmetric difference:  frozenset({67, 10, 12, 45, 23, 89})
Copy of fs:  frozenset({1, 67, 100, 12, 45, 23, 89})

Here,

  • len(s): Returns the length of the frozenset s,
  • x in s: Checks whether x is present in frozenset s or not,
  • x not in s: Returns True if x is not an element of frozenset s. Or else returns False,
  • isdisjoint(other): Returns True if the set has no elements in common with other. Sets are disjoint if and only if their intersection is the empty set.
  • issubset(other): Checks whether other contains elements of the frozenset or not,
  • issuperset(other): Checks whether the frozenset contains elements of other or not,
  • union(*others): Returns a frozenset containing the union of the provided other sets,
  • intersection(*others): Returns a frozenset, with elements common to fs and all others passed,
  • difference(*others): Returns a new frozenset with elements in the frozenset(fs) that are not in the others,
  • symmetric_difference(other): Returns a new frozenset with elements in either fs or other but not both.

Summing Up

That’s it for today. Hope you had a clear understanding of the Python frozenset() method.

For more info, we recommend going through the links provided in the references section.

For any further questions, feel free to comment below.

References