Python - Sets

A frozen set in Python is an immutable, hashable version of a set. Once created, a frozen set cannot be modified by adding or removing elements. It is similar to a set, but it provides an immutable version suitable for situations where immutability is required.

Here's an example demonstrating the concept of a frozen set in Python:

# Creating a set
original_set = {1, 2, 3, 4, 5}

# Creating a frozen set using frozenset()
frozen_set = frozenset(original_set)

# Attempting to add an element to the frozen set (will result in an error)
try:
    frozen_set.add(6)
except AttributeError as e:
    print(f"Error: {e}")

# Displaying the frozen set
print("Original set:", original_set)
print("Frozen set:", frozen_set)

Error: 'frozenset' object has no attribute 'add'
Original set: {1, 2, 3, 4, 5}
Frozen set: frozenset({1, 2, 3, 4, 5})

In this example, a set original_set is created, and then a frozen set frozen_set is created using the frozenset() constructor. Attempting to add an element to the frozen set raises an error, indicating that frozen sets are immutable.

In Python, you can perform a union operation on multiple sets using the union() method or the | (pipe) operator. The union of sets includes all unique elements from the participating sets.

Here's an example demonstrating how to perform a union operation on multiple sets:

# Creating sets
set1 = {1, 2, 3}
set2 = {3, 4, 5}
set3 = {5, 6, 7}

# Using union() method
union_result_method = set1.union(set2, set3)

# Using | operator
union_result_operator = set1 | set2 | set3

# Displaying the results
print("Union using union():", union_result_method)
print("Union using | operator:", union_result_operator)

Union using union(): {1, 2, 3, 4, 5, 6, 7}
Union using | operator: {1, 2, 3, 4, 5, 6, 7}

In this example, three sets (set1, set2, and set3) are created, and the union operation is performed using both the union() method and the | operator. The resulting sets contain all unique elements from the participating sets.

In Python, the update() method is used to update a set by adding elements from another iterable or set. This method modifies the original set in place, adding new elements while eliminating duplicates.

Here's an example demonstrating the use of the update() method:

# Creating a set
set1 = {1, 2, 3}

# Another iterable (list)
list_to_add = [3, 4, 5]

# Using update() method to add elements from the iterable
set1.update(list_to_add)

# Displaying the updated set
print("Updated set:", set1)

Updated set: {1, 2, 3, 4, 5}

In this example, the update() method is used to add elements from the list list_to_add to the original set set1. The resulting set contains all unique elements from both the original set and the iterable.

In Python, you can use the issubset() method or the <= operator to check if one set is a subset of another.

Here's an example demonstrating both methods:

# Creating sets
set1 = {1, 2, 3, 4, 5}
set2 = {2, 4}

# Using issubset() method
is_subset_method = set2.issubset(set1)

# Using <= operator
is_subset_operator = set2 <= set1

# Displaying the results
print("Using issubset() method:", is_subset_method)
print("Using <= operator:", is_subset_operator)

Using issubset() method: True
Using <= operator: True

In this example, set2 is a subset of set1. Both the issubset() method and the <= operator return True when checking if set2 is a subset of set1.