Sets in Python

A set is an unordered collection of items where every element is unique (no duplicates). Sets are mutable, but the elements within a set must be immutable (like strings, numbers, or tuples).

Creating Sets

Sets are created by placing items inside curly braces {} separated by commas, or by using the set() constructor.

# A set of fruits
fruits = {"apple", "banana", "cherry"}

# Creating a set from a list (removes duplicates)
numbers = set([1, 2, 2, 3, 4, 4, 5])
print(numbers) # Output: {1, 2, 3, 4, 5}

# Important: To create an empty set, you must use set(), not {}
empty_set = set()

Adding and Removing Items

Sets are mutable, so you can add and remove items.

fruits = {"apple", "banana"}

# Adding items
fruits.add("orange")

# Adding multiple items
fruits.update(["mango", "grape"])

# Removing items
fruits.remove("banana")  # Raises error if item not found
fruits.discard("cherry") # Does NOT raise error if item not found

# Removing and returning an arbitrary item
item = fruits.pop()

Set Operations

One of the most powerful features of sets is the ability to perform mathematical set operations.

set1 = {1, 2, 3, 4}
set2 = {3, 4, 5, 6}

# Union (all elements from both)
print(set1 | set2) # Output: {1, 2, 3, 4, 5, 6}

# Intersection (only common elements)
print(set1 & set2) # Output: {3, 4}

# Difference (elements in set1 but not in set2)
print(set1 - set2) # Output: {1, 2}

# Symmetric Difference (elements in either set1 or set2, but not both)
print(set1 ^ set2) # Output: {1, 2, 5, 6}

Common Set Methods

Method	Description
`add()`	Adds an element to the set
`clear()`	Removes all elements from the set
`copy()`	Returns a copy of the set
`difference()`	Returns a set containing the difference between two or more sets
`intersection()`	Returns a set that is the intersection of two other sets
`isdisjoint()`	Returns whether two sets have an intersection or not
`issubset()`	Returns whether another set contains this set or not
`union()`	Return a set containing the union of sets

When to Use Sets

When you need to keep track of a collection of items where order doesn’t matter.
When you need to ensure that every item in the collection is unique.
When you need to perform mathematical set operations like intersections or unions.