Python Sets

Frozen Sets

Frozen sets are immutable versions of Python’s built-in set type. This means once a frozen set is created, its elements cannot be added or removed. They are hashable, unlike regular sets, which makes them suitable as keys in dictionaries or elements of other sets.

Key Characteristics:

• Immutability: The defining characteristic. No changes after creation.
• Hashability: Allows use as dictionary keys or set elements.
• Membership Testing: in and not in operators work efficiently.
• Set Operations: Standard set operations (union, intersection, difference, etc.) are supported, but always return new frozen sets.

Creation:

Frozen sets are created using the frozenset() constructor:

my_set = {1, 2, 3}
frozen_set = frozenset(my_set)  # Create a frozen set from a regular set

empty_frozen_set = frozenset() # Create an empty frozen set

another_frozen_set = frozenset(4,5,6) #from a list

Operations:

set1 = frozenset({1, 2, 3})
set2 = frozenset({3, 4, 5})

union_set = set1 | set2  # Union
intersection_set = set1 & set2 # Intersection
difference_set = set1 - set2  # Difference
symmetric_difference_set = set1 ^ set2 #Symmetric Difference

print(f"Union: {union_set}")
print(f"Intersection: {intersection_set}")
print(f"Difference (set1 - set2): {difference_set}")
print(f"Symmetric Difference: {symmetric_difference_set}")

#Membership testing
print(f"Is 3 in set1? {3 in set1}")

#Attempting to modify (will raise an error)
# set1.add(4) # AttributeError: 'frozenset' object has no attribute 'add'

Use Cases:

• Dictionary keys: Because they are hashable.
• Representing constant collections of data where immutability is desired.
• Data structures that require elements to be unique and unchanging.

Set Operations (Python Sets)