Python Sets Complete Master Notes & Practice Questions

1. What is a Set in Python?

English Definition

A Set is an unordered, unindexed collection of unique elements in Python. Sets do not allow duplicate values and are defined using curly brackets {} or the set() constructor.

Hinglish Explanation

Set Python mein ek aisa data structure hai jisme unique values store hoti hain. Jab hum set banate hain to duplicate values automatically remove ho jaati hain aur iska element order fixed nahi hota.

Unordered: Elements have no defined order and may appear in different order when printed.
Unique Elements: Duplicate entries are automatically discarded upon creation.
Unindexed: Elements cannot be accessed using index numbers like set[0].
Mutable Set Container: We can add or remove elements after creation.

2. Creating a Set & Automatic Duplicate Removal

Sets are created using curly brackets {}. Notice how duplicate numbers like 20 and 40 are automatically filtered out when printed.

Python Code - Creating a Set with Duplicates

numbers = {10, 20, 30, 40, 50, 40, 20, "gagan", -944, 2.5}
print("Set Output:", numbers)

Output (Order may vary)

Set Output: {2.5, 40, 10, 50, 'gagan', 20, -944, 30}

3. Sets Cannot Use Indexing

Why Indexing Fails

Since sets are unordered collections without positional indices, attempting to access elements via square brackets numbers[0] will raise a TypeError.

Hinglish Explanation

Sets unordered hote hain, isliye inme indexing kaam nahi karti. numbers[0] likhne par Python error dega.

Python Code - Attempting Indexing

numbers = {10, 20, 30}
try:
    print(numbers[0])
except TypeError as e:
    print("Error:", e)

Output

Error: 'set' object is not subscriptable

4. Traversing (Looping) & Length of a Set

Even though sets cannot be indexed, you can easily iterate over set items using a for loop or count elements using len().

Python Code - Loop & len()

numbers = {10, 20, 30, 40}

print("Total elements (len):", len(numbers))

print("Iterating over set elements:")
for item in numbers:
    print(item)

Output

Total elements (len): 4
Iterating over set elements:
40
10
20
30

5. Adding Elements (add vs update)

Method	Syntax	Description
add()	`set.add(element)`	Adds a single element to the set.
update()	`set.update(iterable)`	Adds multiple elements from a list, tuple, or another set.

Python Code - add() and update()

numbers = {10, 20}
numbers.add(30)
print("After add(30):", numbers)

numbers.update([40, 50, 60])
print("After update([40, 50, 60]):", numbers)

Output

After add(30): {10, 20, 30}
After update([40, 50, 60]): {40, 10, 50, 20, 60, 30}

6. Removing Elements (remove, discard, pop, clear)

remove() vs discard() Critical Difference

remove(x): Deletes x. Raises a KeyError if x is not present in the set.

discard(x): Deletes x. Does NOT raise any error if x is missing.

Hinglish Explanation

remove() error deta hai agar value set mein na mile. Jabki discard() safe method hai, element na milne par silently skip ho jata hai bina error diye.

Python Code - Deleting Set Items

numbers = {10, 20, 30, 40, 50}

numbers.remove(20)
print("After remove(20):", numbers)

numbers.discard(100)
print("After discard(100) [No error]:", numbers)

popped_item = numbers.pop()
print("Popped random element:", popped_item)
print("After pop():", numbers)

numbers.clear()
print("After clear():", numbers)

Output

After remove(20): {40, 10, 50, 30}
After discard(100) [No error]: {40, 10, 50, 30}
Popped random element: 40
After pop(): {10, 50, 30}
After clear(): set()

7. Mathematical Set Operations

Operation	Operator	Method	Description
Union	`a \| b`	`a.union(b)`	Combines elements from both sets (no duplicates).
Intersection	`a & b`	`a.intersection(b)`	Extracts only common elements present in both sets.
Difference	`a - b`	`a.difference(b)`	Elements in `a` that are not in `b`.
Symmetric Difference	`a ^ b`	`a.symmetric_difference(b)`	Elements in either set, but not in both (removes common).

Python Code - Set Operations

a = {1, 2, 3, 4}
b = {3, 4, 5, 6}

print("Union (a | b):", a | b)
print("Intersection (a & b):", a & b)
print("Difference (a - b):", a - b)
print("Symmetric Difference (a ^ b):", a ^ b)

Output

Union (a | b): {1, 2, 3, 4, 5, 6}
Intersection (a & b): {3, 4}
Difference (a - b): {1, 2}
Symmetric Difference (a ^ b): {1, 2, 5, 6}

8. Important Set Methods Summary

Method	Action / Usage
`add(val)`	Adds a single element to the set.
`update(seq)`	Adds multiple elements from any iterable.
`remove(val)`	Deletes element (raises KeyError if missing).
`discard(val)`	Deletes element without throwing an error if missing.
`pop()`	Removes and returns an arbitrary random element.
`clear()`	Removes all items, leaving an empty set `set()`.
`union()`	Returns a new set with all items from both sets.
`intersection()`	Returns a new set with common elements.
`difference()`	Returns elements present in first set only.
`symmetric_difference()`	Returns non-overlapping elements from both sets.

9. Real-Life Applications of Python Sets

1. Duplicate Removal: Easily converting lists with duplicates into sets (e.g. list(set(raw_data))).
2. Fast Membership Testing: Checking if an item exists in O(1) time complexity compared to O(n) in lists.
3. Mathematical Data Operations: Finding common followers, mutual friends, shared interests across datasets.
4. Data Comparison & Filtering: Comparing differences between two database tables or log files.

10. Set Practice Questions List

Set Practice Questions

1. Create a set with 5 numbers and print it.

2. Add an element to a set using add().

3. Add multiple elements to a set using update().

4. Remove an element from a set using remove().

5. Remove an element safely using discard().

6. Print the total count of elements using len().

7. Print all elements using a for loop.

8. Find the union of two sets using union().

9. Find the intersection of two sets using intersection().

10. Find the difference of two sets using difference().

11. Find the symmetric difference of two sets using symmetric_difference().

11. Step-by-Step Python Code Solutions

Python Code - Practice Solutions (Q1 - Q11)

numbers = {10, 20, 30, 40, 50}
print("1. Set:", numbers)

s2 = {10, 20, 30}
s2.add(40)
print("2. After add(40):", s2)

s3 = {10, 20}
s3.update([30, 40, 50])
print("3. After update([30, 40, 50]):", s3)

s4 = {10, 20, 30}
s4.remove(20)
print("4. After remove(20):", s4)

s5 = {10, 20, 30, 40}
print("5. Length:", len(s5))

s6 = {10, 20, 30}
print("6. Loop Items:")
for item in s6:
    print("  -", item)

a = {1, 2, 3}
b = {3, 4, 5}
print("7. Union:", a.union(b))

a = {1, 2, 3}
b = {2, 3, 4}
print("8. Intersection:", a.intersection(b))

a = {1, 2, 3}
b = {2, 3, 4}
print("9. Difference (a - b):", a.difference(b))

a = {1, 2, 3}
b = {3, 4, 5}
print("10. Symmetric Difference:", a.symmetric_difference(b))

Output

1. Set: {40, 10, 50, 20, 30}
2. After add(40): {40, 10, 20, 30}
3. After update([30, 40, 50]): {40, 10, 50, 20, 30}
4. After remove(20): {10, 30}
5. Length: 4
6. Loop Items:
- 10
- 20
- 30
7. Union: {1, 2, 3, 4, 5}
8. Intersection: {2, 3}
9. Difference (a - b): {1}
10. Symmetric Difference: {1, 2, 4, 5}

Python Sets Master

Python Sets: Complete Master Notes & Practice Solutions

1. What is a Set in Python?

English Definition

Hinglish Explanation

2. Creating a Set & Automatic Duplicate Removal

3. Sets Cannot Use Indexing

Why Indexing Fails

Hinglish Explanation

4. Traversing (Looping) & Length of a Set

5. Adding Elements (add vs update)

6. Removing Elements (remove, discard, pop, clear)

remove() vs discard() Critical Difference

Hinglish Explanation

7. Mathematical Set Operations

8. Important Set Methods Summary

9. Real-Life Applications of Python Sets

10. Set Practice Questions List

11. Step-by-Step Python Code Solutions