Python set(): Create an Unordered Collection of Unique Elements

The set() function creates a collection of unique, unordered items. It’s useful for removing duplicates, performing set operations (union, intersection), and improving membership tests.

Example

numbers = [1, 2, 2, 3, 4, 4, 5]
unique_numbers = set(numbers)
print(unique_numbers)

Output:

{1, 2, 3, 4, 5}

Duplicates are removed automatically.

Syntax

set(iterable)

iterable (optional) → A sequence (list, tuple, string) to convert into a set.
Returns → A set of unique elements.

1. Creating a Set from a List

fruits = ["apple", "banana", "apple", "cherry"]
fruit_set = set(fruits)
print(fruit_set)
# Output: {'banana', 'cherry', 'apple'}

Sets remove duplicates automatically.

2. Creating an Empty Set

empty_set = set()  # Correct way
print(type(empty_set))  # Output: <class 'set'>

Do not use {} → This creates an empty dictionary, not a set.

3. Checking Membership in a Set (`in`)

numbers = {1, 2, 3, 4}
print(2 in numbers)  # Output: True
print(5 in numbers)  # Output: False

Faster than checking in a list or tuple.

4. Adding and Removing Items in a Set

s = {1, 2, 3}
s.add(4)  # Adds 4
s.remove(2)  # Removes 2
print(s)  # Output: {1, 3, 4}

add(x) → Adds x to the set.
remove(x) → Removes x (raises error if missing).
discard(x) → Removes x (no error if missing).

5. Set Operations (Union, Intersection, Difference)

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

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

| (Union) → Combines elements.
& (Intersection) → Finds common elements.
- (Difference) → Elements in a but not b.

Key Notes

✔ Stores unique, unordered elements.
✔ Removes duplicates automatically.
✔ Supports fast membership checks (in).
✔ Supports set operations (union, intersection, difference).

By using set(), you can handle unique values efficiently, compare collections, and perform fast lookups. 🚀