freeCodeCamp/guide/english/python/frozenset/index.md

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Python Frozenset

frozenset basic info
The frozenset type is a builtin set types which is immutable and hashable -- its contents cannot be altered after it is created; however, it can be used as a dictionary key or as an element of another set. Frozensets are like sets except that they cannot be changed, i.e they are immutale.

>>> cities = frozenset(["Frankfurt", "Basel", "Freiburg"])
>>> cities.add("Strasbourg")
Traceback (most recent call last):
    File "<stdin>", line 1, in <module>
AttributeError: 'frozenset' object has no attribute 'add'
>>>

frozenset constructor:
frozenset([iterable])
The iterable contains elements to initialize the frozenset with. The iterable can be set, dictionary, tuple etc. If no parameter is passed, the frozenset() method returns an empty frozenset.

Examples

>>> vowels = ('a', 'e', 'i', 'o', 'u')
>>> fSet = frozenset(vowels)
>>> print("The frozen set is: ", fSet)
The frozen set is: frozenset({'i', 'e', 'a', 'u', 'o'})
>>> print("The empty frozen set is: ", frozenset())
The empty frozen set is: frozenset()
>>>

Another Example

>>> person = {"name": "John", "age": 23, "sex": "male"}
>>> fSet = frozenset(person)
>>> print("The frozen set is: ", fSet)
The frozen set is: frozenset({'sex', 'name', 'age'})
>>>

Additional Information
Python Frozenset()
Set Types -- set, frozenset
Python Tutorial: Sets and Frozen sets