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Explain about the Python Sets.

ICSM 745 22-Sep-2025

Explain about the Python Sets. with example line by line.

python-3.4 Python 3

Updated on 24-Sep-2025

ICSM

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1 Answers

Anubhav Kumar

22-Sep-2025

1. What is a Set in Python?

A set is a built-in Python data type used to store unordered, unique elements.

Unordered → Elements have no fixed order.
Unique → No duplicate values are allowed.
Mutable → You can add or remove elements, but elements themselves must be immutable (like numbers, strings, tuples — but not lists or dictionaries).

2. Creating a Set

# Empty set
my_set = set()

# Set with values
fruits = {"apple", "banana", "cherry"}
print(fruits)   # {'apple', 'banana', 'cherry'}

# Duplicates are ignored
nums = {1, 2, 2, 3, 4}
print(nums)     # {1, 2, 3, 4}

{} creates an empty dictionary, not a set. Always use set() for an empty set.

3. Accessing Elements

Since sets are unordered, they don’t support indexing (set[0]).
You loop through them:

for fruit in fruits:
    print(fruit)

4. Adding & Removing Elements

fruits.add("orange")        # Add single element
print(fruits)

fruits.update(["grape", "mango"])  # Add multiple elements
print(fruits)

fruits.remove("banana")     # Removes element (raises error if not found)
fruits.discard("pear")      # Removes element (NO error if not found)

fruits.pop()                # Removes a random element
fruits.clear()              # Removes all elements

5. Set Operations

Sets are powerful for mathematical operations:

A = {1, 2, 3, 4}
B = {3, 4, 5, 6}

print(A | B)   # Union → {1, 2, 3, 4, 5, 6}
print(A & B)   # Intersection → {3, 4}
print(A - B)   # Difference → {1, 2}
print(A ^ B)   # Symmetric Difference → {1, 2, 5, 6}

6. Set Methods

print(A.issubset(B))      # False
print(A.issuperset(B))    # False
print(A.isdisjoint(B))    # False (they share 3,4)

7. Frozen Sets (Immutable Sets)

If you need an immutable set (cannot be changed):

frozen = frozenset([1, 2, 3])
print(frozen)
# frozen.add(4) ❌ → Error

8. Example Use Cases

Removing duplicates from a list:

nums = [1, 2, 2, 3, 4, 4, 5]
unique_nums = set(nums)
print(unique_nums)   # {1, 2, 3, 4, 5}

Membership testing (faster than lists):

print(3 in A)   # True
print(7 in A)   # False

Summary:

Set = unordered, unique, mutable collection.
Supports mathematical set operations (union, intersection, difference).
Great for removing duplicates & fast membership checks.
Use frozenset if you need immutability.