Lists & Collections — Lesson 4: Build a score leaderboard

New skill: Sorted lists, reverse order and preserving data
Previously learned: Units 01–07

Why this matters

Sorting is useful for game rankings, robotics competitions, and class progress views.

Step 1 — Explore working Python

Read the program below. Before running it, write down the result you expect.

scores = [12, 28, 19]
ranked = sorted(scores, reverse=True)
print(ranked)
print(scores)

Step 2 — Trace the code

1. Use sorted() to create a new ordered list.
2. Set reverse=True to put larger values first.
3. Use a slice to select only the two top results.

Step 3 — Check your understanding

What are the first two values of sorted([7, 9, 9, 3], reverse=True)?

Step 4 — Watch for this mistake

.sort() changes a list in place and returns None; sorted() creates a new list.

Practice: Build a score leaderboard

Complete top_two(scores) to return the two highest scores in descending order. Duplicates count. There will be at least two scores.

Function contract: top_two(scores)
Starter file: main.py

Work in the editor, using Run to explore and Check to compare against the published examples. Your submitted code, not the public check, determines the recorded score.

Hint 1 — Start

Make a descending copy with `sorted()`.

Hint 2 — Build

Use `reverse=True` rather than manually swapping values.

Hint 3 — Test

Return a slice containing the first two items.

Reflect

In 3–5 sentences, explain the algorithm you chose, one test case you predicted, and how you would detect an incorrect answer.

Optional reading

For another perspective on this skill, see How to Think Like a Computer Scientist (interactive textbook). This Playground lesson, worked example, and exercise are original; no textbook passages were reproduced.