Python Set Explained

📌 What is a Set?

A set in Python is a collection of unique, unordered elements. Sets are mainly used when you want to store items without duplicates and perform mathematical set operations like union, intersection, and difference.

Unordered: Elements do not have a fixed order.
No duplicates: Duplicate elements are automatically removed.
Mutable: You can add or remove items.
Elements must be immutable (numbers, strings, tuples).

📝 Creating a Set


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

# Set with data
fruits = {"apple", "banana", "cherry"}

print(fruits)  # {'banana', 'cherry', 'apple'}

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

⚡ Adding & Removing Elements


fruits = {"apple", "banana"}

# Add element
fruits.add("cherry")

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

# Remove element (error if not found)
fruits.remove("banana")

# Remove element safely (no error if not found)
fruits.discard("orange")

# Remove and return a random element
fruits.pop()

# Clear all elements
fruits.clear()

print(fruits)  # set()

🛠️ Common Set Methods

Method	Description	Example
`set.add(x)`	Adds element x	`fruits.add("apple")`
`set.update(iterable)`	Adds multiple elements	`fruits.update(["mango","grape"])`
`set.remove(x)`	Removes element x (error if missing)	`fruits.remove("apple")`
`set.discard(x)`	Removes element x (no error if missing)	`fruits.discard("apple")`
`set.pop()`	Removes and returns a random element	`fruits.pop()`
`set.clear()`	Removes all elements	`fruits.clear()`
`set.union()`	Returns union of sets	`a.union(b)`
`set.intersection()`	Returns common elements	`a.intersection(b)`
`set.difference()`	Returns elements in A not in B	`a.difference(b)`
`set.symmetric_difference()`	Returns elements not common to both	`a.symmetric_difference(b)`
`set.issubset()`	Checks if A is subset of B	`a.issubset(b)`
`set.issuperset()`	Checks if A is superset of B	`a.issuperset(b)`
`set.isdisjoint()`	Checks if A and B have no elements in common	`a.isdisjoint(b)`

📚 Set Operations


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

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

🎯 Uses of Sets

Removing duplicates from a list.
Efficient membership testing (in keyword).
Performing mathematical set operations.
Storing unique items (e.g., unique users, unique words).


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

🔑 Key Points to Remember

Sets are unordered → no indexing.
No duplicates allowed.
Useful for fast lookups and unique collections.
Supports powerful set operations.