Introduction To Python (Chapter: 3)

1. What is a Set in Python?

A Set is a built-in data type in Python that stores multiple items. It is unordered, does not allow duplicate values, and is mutable.

It works similar to a mathematical set.

my_set = {1, 2, 3, 4}
print(my_set)

Output:
{1, 2, 3, 4}

2. Important Properties of Set

Unordered
No Duplicates
Mutable
No Indexing

numbers = {1, 2, 2, 3, 4, 4}
print(numbers)

Output:
{1, 2, 3, 4}

3. Creating a Set

Method 1: Using Curly Braces

fruits = {"apple", "banana", "mango"}
print(fruits)

Method 2: Using set() Constructor

numbers = set([1, 2, 3, 4])
print(numbers)

Important: {} creates a dictionary, not a set.

empty_set = set()

4. Accessing Set Elements

Sets are unordered, so indexing is not allowed.

my_set[0]   # Error

You can loop through elements.

colors = {"red", "green", "blue"}

for color in colors:
    print(color)

5. Adding Elements

add() adds a single element.

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

update() adds multiple elements.

numbers = {1, 2}
numbers.update([3, 4, 5])
print(numbers)

6. Removing Elements

remove() removes element and gives error if not found.

numbers = {1, 2, 3}
numbers.remove(2)
print(numbers)

discard() does not give error if element not found.

numbers = {1, 2, 3}
numbers.discard(5)
print(numbers)

pop() removes random element.

numbers = {1, 2, 3}
numbers.pop()
print(numbers)

clear() removes all elements.

numbers = {1, 2, 3}
numbers.clear()
print(numbers)

7. Set Operations

Union combines two sets.

A = {1, 2, 3}
B = {3, 4, 5}

print(A | B)
print(A.union(B))

Intersection finds common elements.

print(A & B)
print(A.intersection(B))

Difference finds elements in A but not in B.

print(A - B)
print(A.difference(B))

Symmetric Difference finds non-common elements.

print(A ^ B)
print(A.symmetric_difference(B))

8. Set Comparison Methods

A = {1, 2}
B = {1, 2, 3}

print(A.issubset(B))
print(B.issuperset(A))
print(A.isdisjoint({4, 5}))

9. Frozen Set

A frozenset is an immutable version of set. It cannot be modified.

fs = frozenset([1, 2, 3])
print(fs)

fs.add(4)   # Error

10. When to Use Set?

Remove duplicates
Fast membership checking
Perform mathematical operations
Order is not important

11. Practical Real Example

Removing duplicate students from list.

students = ["Ravi", "Amit", "Ravi", "Sita", "Amit"]

unique_students = set(students)

print(unique_students)

12. Important Built-in Functions

numbers = {1, 2, 3, 4}

print(len(numbers))
print(max(numbers))
print(min(numbers))
print(sum(numbers))

Final Summary

Set = Unordered + No duplicates
No indexing
Supports mathematical operations
Mutable (except frozenset)
Very fast for membership checking

Python - Set