Python Sets and Set Operations

What is a Set in Python?

A set is an unordered, unindexed, and mutable collection of unique elements. It is defined using curly braces {} or the set() function.

Basic Set Syntax:

my_set = {1, 2, 3, 4}
print(my_set)

Output:

{1, 2, 3, 4}

Duplicates are automatically removed in a set.

Creating a Set

# From a list
set1 = set([1, 2, 3, 3])
print(set1)  # {1, 2, 3}

# Using curly braces
set2 = {4, 5, 6}

Accessing Set Items

Sets are unordered, so you cannot access items by index.

for item in set1:
    print(item)

Add & Update Items in a Set

Add an element:

set1.add(4)
print(set1)

Update multiple items:

set1.update([5, 6])
print(set1)

Remove Elements from a Set

set1.remove(2)   # Removes 2; throws error if not found
set1.discard(10) # Safe remove; no error if not found
set1.pop()       # Removes a random element
set1.clear()     # Empties the set

Python Set Operations (with Examples)

Let's define two sets for demonstration:

a = {1, 2, 3, 4}
b = {3, 4, 5, 6}

1. Union (| or .union())

Combines elements from both sets without duplicates.

print(a | b)
print(a.union(b))

Output:

{1, 2, 3, 4, 5, 6}

2. Intersection (& or .intersection())

Gets common elements in both sets.

print(a & b)
print(a.intersection(b))

Output:

{3, 4}

3. Difference (- or .difference())

Elements in a but not in b.

print(a - b)
print(a.difference(b))

Output:

{1, 2}

4. Symmetric Difference (^ or .symmetric_difference())

Elements in either set but not both.

print(a ^ b)
print(a.symmetric_difference(b))

Output:

{1, 2, 5, 6}

5. Set Membership Test

print(3 in a)     # True
print(10 not in b)  # True

Advanced Set Methods

Frozen Sets in Python

A frozenset is immutable and hashable.

fs = frozenset([1, 2, 3])
# fs.add(4) Will raise an error