A set in Python is an unordered, mutable, and unindexed collection of unique elements. Sets are commonly used when you need to store distinct values and perform operations like union, intersection, and difference.

Key Features of Sets

1. Unordered: Sets do not maintain the order of their elements.
2. Unique Elements: Duplicate elements are automatically removed.
3. Mutable: Sets can be modified (e.g., adding or removing elements).
4. Unindexed: You cannot access elements by index.
5. Optimized Operations: Sets are optimized for membership tests (e.g., in or not in).

Creating Sets

You can create a set by enclosing elements in curly braces {} or using the set() constructor.

# Empty set (must use set(), not {})
empty_set = set()

# Set with integers
int_set = {1, 2, 3}

# Set with mixed data types
mixed_set = {1, "hello", 3.14}

# Set with duplicate elements (duplicates are removed automatically)
unique_set = {1, 2, 2, 3, 3, 3}
print(unique_set)  # Output: {1, 2, 3}

Accessing Elements

Since sets are unordered, you cannot access elements by index. However, you can iterate through a set using a loop.

fruits = {"apple", "banana", "cherry"}

# Iterating through a set
for fruit in fruits:
    print(fruit)

# Checking membership
print("apple" in fruits)  # Output: True
print("grape" in fruits)  # Output: False

Set Methods

Basic Set Operations

Adding Elements

numbers = {1, 2, 3}
numbers.add(4)
print(numbers)  # Output: {1, 2, 3, 4}

Removing Elements

numbers = {1, 2, 3}
numbers.remove(2)  # Removes 2
# numbers.remove(5)  # Raises KeyError if element not found

numbers.discard(5)  # Does not raise an error if element not found
print(numbers)  # Output: {1, 3}

Union

Combines all unique elements from two sets.

set1 = {1, 2, 3}
set2 = {3, 4, 5}
print(set1.union(set2))  # Output: {1, 2, 3, 4, 5}

Intersection

Finds common elements between two sets.

set1 = {1, 2, 3}
set2 = {3, 4, 5}
print(set1.intersection(set2))  # Output: {3}

Difference

Finds elements in one set but not in the other.

set1 = {1, 2, 3}
set2 = {3, 4, 5}
print(set1.difference(set2))  # Output: {1, 2}

Symmetric Difference

Finds elements in either set but not both.

set1 = {1, 2, 3}
set2 = {3, 4, 5}
print(set1.symmetric_difference(set2))  # Output: {1, 2, 4, 5}

Frozen Sets

A frozenset is an immutable version of a set. You cannot modify its elements after creation.

fs = frozenset([1, 2, 3, 3])
print(fs)  # Output: frozenset({1, 2, 3})

# fs.add(4)  # Raises AttributeError: 'frozenset' object has no attribute 'add'

Example: Removing Duplicates Using Sets

# Removing duplicates from a list
numbers = [1, 2, 2, 3, 4, 4, 5]
unique_numbers = set(numbers)
print(unique_numbers)  # Output: {1, 2, 3, 4, 5}

Use Cases of Sets

1. Membership Testing: Quickly check if an item exists in a collection.
2. Removing Duplicates: Convert a list to a set to eliminate duplicates.
3. Mathematical Operations: Perform union, intersection, and difference for data analysis.

Comparison with Lists and Tuples

Conclusion

Python sets are versatile for working with unique collections of data and performing efficient mathematical operations. Their unordered and unique nature makes them an excellent choice for tasks involving membership testing, data deduplication, and set-based operations.