Python frozenset() Function
Python3 Built-in Functionsfrozenset()is a built-in function in Python used to create an immutable set (frozenset).
The difference between frozenset and set is that frozenset is immutable; after creation, elements cannot be added, removed, or modified. Due to its immutability, frozenset can be used as dictionary keys or elements of a set.
Word Definition： frozensetis the abbreviation for "frozen set," representing an immutable set.
Basic Syntax and Parameters
Syntax Format
frozenset(iterable)
Parameter Description
- Parameter iterable：
- Type: iterable object
- Description: The iterable object to convert to an immutable set.
Function Description
- Return value: Returns a frozenset object.
- Special value: Returns an empty frozenset when called without arguments.
Examples
Example 1: Creating a frozenset
Example
# Create from a list
lst = [1, 2, 3, 2, 1]
fs = frozenset(lst)
print(fs) # Output: frozenset({1, 2, 3})
# Create from a string
s = "hello"
fs = frozenset(s)
print(fs) # Output: frozenset({'h', 'e', 'l', 'o'})
# Create from a dictionary (keys)
d = {"a": 1, "b": 2}
fs = frozenset(d)
print(fs) # Output: frozenset({'a', 'b'})
# Empty frozenset
fs = frozenset()
print(fs) # Output: frozenset()
lst = [1, 2, 3, 2, 1]
fs = frozenset(lst)
print(fs) # Output: frozenset({1, 2, 3})
# Create from a string
s = "hello"
fs = frozenset(s)
print(fs) # Output: frozenset({'h', 'e', 'l', 'o'})
# Create from a dictionary (keys)
d = {"a": 1, "b": 2}
fs = frozenset(d)
print(fs) # Output: frozenset({'a', 'b'})
# Empty frozenset
fs = frozenset()
print(fs) # Output: frozenset()
Expected output:
frozenset({1, 2, 3})
frozenset({'h', 'e', 'l', 'o'})
frozenset({'a', 'b'})
frozenset()
Code analysis:
- frozenset automatically removes duplicates.
- It can be used with various iterable objects.
- frozenset is immutable and does not have methods like add or remove.
Example 2: Uses of frozenset
Example
# frozenset can be used as dictionary keys
d = {frozenset([1, 2]): "A", frozenset([3, 4]): "B"}
print(d) # Output: {frozenset({1, 2}): 'A', frozenset({3, 4}): 'B'}
# frozenset can be elements of a set
s = {frozenset([1, 2]), frozenset([3, 4])}
print(s) # Output: {frozenset({1, 2}), frozenset({3, 4})}
# frozenset supports set operations (but does not modify the original set)
fs1 = frozenset([1, 2, 3])
fs2 = frozenset([2, 3, 4])
print(fs1 & fs2) # Output: frozenset({2, 3}) intersection
print(fs1 | fs2) # Output: frozenset({1, 2, 3, 4}) union
d = {frozenset([1, 2]): "A", frozenset([3, 4]): "B"}
print(d) # Output: {frozenset({1, 2}): 'A', frozenset({3, 4}): 'B'}
# frozenset can be elements of a set
s = {frozenset([1, 2]), frozenset([3, 4])}
print(s) # Output: {frozenset({1, 2}), frozenset({3, 4})}
# frozenset supports set operations (but does not modify the original set)
fs1 = frozenset([1, 2, 3])
fs2 = frozenset([2, 3, 4])
print(fs1 & fs2) # Output: frozenset({2, 3}) intersection
print(fs1 | fs2) # Output: frozenset({1, 2, 3, 4}) union
Expected output:
{frozenset({1, 2}): 'A', frozenset({3, 4}): 'B'}
{frozenset({1, 2}), frozenset({3, 4})}
frozenset({2, 3})
frozenset({1, 2, 3, 4})
The main use of frozenset is as dictionary keys or elements of a set.
Other Extensions