Lesson 12 — Sets

Unique values

A set stores each value only once and has no fixed order. Create one with curly braces or by passing a list to set(), and duplicates disappear automatically. Checking x in my_set is also very fast, even for huge sets.

tags = set(["python", "web", "python"])
print(len(tags))  # 2

Why it matters: removing duplicates — repeated emails, visitors, tags — is one of the most common data-cleaning jobs.