Day 19: Sets

Quick Answer

What You Will Learn

• {1, 2, 3} creates a set inside curly brackets. An empty set must be written as set().
• a | b is the union: all unique items from both sets.
• a & b is the intersection: only items present in both sets.
• a - b is the difference: items only in a.
• set(visits) removes duplicate visits, which is how you count unique visitors.

Code

a = {1, 2, 3}
b = {2, 3, 4}
print(a | b)
print(a & b)
print(a - b)
print(a ^ b)
visits = ["u1", "u2", "u1", "u3"]
print(len(set(visits)))
print(set())

Output

{1, 2, 3, 4}
{2, 3}
{1}
{1, 4}
3
set()

Code Explained, Line by Line

1. {1, 2, 3} creates a set inside curly brackets. An empty set must be written as set().
2. a | b is the union: all unique items from both sets.
3. a & b is the intersection: only items present in both sets.
4. a - b is the difference: items only in a.
5. set(visits) removes duplicate visits, which is how you count unique visitors.

Real-Life Use

Unique visitors, common friends and duplicate removal all use sets.

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