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Python Basics · Data Structures · Lesson 18 of 36

Sets

Concept

Sets

Sets store unique, unordered values, useful for removing duplicates or checking membership quickly.

Checking whether a value is in a set with in is much faster than checking a list, especially as the collection grows large.

By the end of this lesson
  • Explain the core idea behind Sets.
  • Predict output before running a change.
  • Test one realistic and one unusual input.
  • Use the result to make the next decision.
How to study this page
  1. 1. Read one concept.
  2. 2. Change the example.
  3. 3. Run, compare, and explain.
  4. 4. Complete the challenge below.
Syntax
my_set = {value1, value2}
set(some_list)
ExampleRunnable
numbers = {1, 2, 2, 3, 3, 3}
print(numbers)
print(2 in numbers)
Try it Yourself »
Deduplicating a list
nums = [1, 2, 2, 3, 3, 3]
unique = list(set(nums))
print(unique)
Self-check before continuing

Without looking at the example, describe what changes when you modify one input in Sets. Then reopen the editor and prove your explanation with a small test.

You are ready to continue when you can predict, test, and explain the result.

Your turn

Create a set from a list with duplicate values and print its length.

Loading editor…

Console

Output will appear here...