Index
A set in Python is an unordered, mutable, and unindexed collection of unique elements. It is useful when you need to store multiple items without duplicates and perform set operations like union, intersection, and difference.
1. Creating a Set
A set is defined using curly braces {} or the set() function.
# Creating a set
fruits = {"apple", "banana", "cherry"}
print(fruits) # Output: {'banana', 'cherry', 'apple'}
# Using set() function
numbers = set([1, 2, 3, 4, 5])
print(numbers) # Output: {1, 2, 3, 4, 5}
✅ Key Points:
- Sets do not allow duplicate values.
- The order of elements is not guaranteed (unordered).
- Sets do not support indexing (no
set[0]).
2. Adding Elements to a Set
You can add elements using add() (for a single element) and update() (for multiple elements).
# Adding a single element
fruits.add("orange")
print(fruits) # Output: {'banana', 'cherry', 'apple', 'orange'}
# Adding multiple elements
fruits.update(["grape", "mango"])
print(fruits) # Output: {'banana', 'cherry', 'apple', 'orange', 'grape', 'mango'}
3. Removing Elements from a Set
You can remove elements using remove(), discard(), or pop().
# Removing a specific element (raises an error if not found)
fruits.remove("banana")
print(fruits) # Output: {'cherry', 'apple', 'orange', 'grape', 'mango'}
# Using discard() (no error if element is missing)
fruits.discard("grape")
print(fruits) # Output: {'cherry', 'apple', 'orange', 'mango'}
# Using pop() (removes a random element)
removed_element = fruits.pop()
print(fruits) # Output: Set without one random element
print("Removed:", removed_element)
✅ Note:
remove()raises an error if the element doesn’t exist.discard()does not raise an error.pop()removes a random element.
4. Checking Membership in a Set
Use in and not in to check if an item exists in a set.
fruits = {"apple", "banana", "cherry"}
print("apple" in fruits) # Output: True
print("grape" not in fruits) # Output: True
5. Set Operations
Python sets support operations like union, intersection, difference, and symmetric difference.
| Operation | Method | Symbol | Description |
|---|---|---|---|
| Union | set1.union(set2) | `set1 | set2` |
| Intersection | set1.intersection(set2) | set1 & set2 | Common elements in both sets |
| Difference | set1.difference(set2) | set1 - set2 | Elements in set1 but not in set2 |
| Symmetric Difference | set1.symmetric_difference(set2) | set1 ^ set2 | Elements in either set1 or set2, but not both |
Example:
A = {1, 2, 3, 4, 5}
B = {4, 5, 6, 7, 8}
print(A | B) # Union → {1, 2, 3, 4, 5, 6, 7, 8}
print(A & B) # Intersection → {4, 5}
print(A - B) # Difference → {1, 2, 3}
print(A ^ B) # Symmetric Difference → {1, 2, 3, 6, 7, 8}
6. Set Methods
| Method | Description |
|---|---|
add(x) | Adds x to the set |
update(iterable) | Adds multiple elements |
remove(x) | Removes x (error if missing) |
discard(x) | Removes x (no error if missing) |
pop() | Removes a random element |
clear() | Removes all elements |
union(set2) | Combines two sets |
intersection(set2) | Finds common elements |
difference(set2) | Elements in set1 but not set2 |
symmetric_difference(set2) | Elements in set1 or set2, but not both |
issubset(set2) | Checks if set1 is a subset of set2 |
issuperset(set2) | Checks if set1 is a superset of set2 |
7. Subsets & Supers
A = {1, 2, 3}
B = {1, 2, 3, 4, 5}
print(A.issubset(B)) # True (A is a subset of B)
print(B.issuperset(A)) # True (B is a superset of A)
8. Frozen Sets (Immutable Sets)
A frozen set is an immutable version of a set.
frozen_set = frozenset([1, 2, 3, 4])
# frozen_set.add(5) # TypeError: 'frozenset' object has no attribute 'add'
print(frozen_set) # Output: frozenset({1, 2, 3, 4})