Sets and unique values

A set contains unique values. It does not provide list-style indexing, and you should not rely on its iteration order. Use a set when uniqueness or membership matters.

subjects = {"Python", "SQL", "Python"}
print(len(subjects))
print("SQL" in subjects)
subjects.add("Excel")
print("Excel" in subjects)

2
True
True

Create a set from another collection

Use set() to remove duplicate values from a list. Use set() with no arguments to make an empty set; {} creates an empty dictionary.

topics = ["loops", "files", "loops"]
unique_topics = set(topics)
print(len(unique_topics))
print("loops" in unique_topics)

2
True

Why this works

A set is useful when you care whether a value is present or how many distinct values you have. Duplicate entries collapse into one. Sets are not position-based: membership works, but indexing does not. Convert to a sorted list only when you need a predictable display order.

Practice

Create a list containing repeated topic names, convert it to a set, and check its length. Do not assume a particular order when printing the set.

Try another case

How many values remain in set(["SQL", "Python", "SQL", "Excel"])?