Rankings: Top-N with sorted & max

13 min 35 XP

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Step 1

Learn the idea

Every dashboard has a leaderboard: best sellers, slowest pages, biggest customers. In Python a ranking is three moves:

items.items() — get (name, number) pairs out of a dict
sorted(..., key=lambda pair: pair[1], reverse=True) — order by the number, biggest first
[:3] — slice the podium

Need just the single winner? max(data, key=data.get) reads almost like English. And enumerate(top, start=1) numbers your report lines without a manual counter.

Where you'll use this

Top-N queries power every leaderboard, 'best sellers' shelf, alerting system ('5 slowest endpoints') and recommendation panel. It's among the most-run query shapes in industry.

Common mistakes

Sorting the dict instead of its .items() — you'll rank keys alphabetically and wonder where the numbers went.
Forgetting reverse=True and shipping a bottom-3 as your top-3.
Slicing before sorting — [:3] on unsorted items is just the first three, not the best three.

Pro tip

For huge datasets, heapq.nlargest(3, units.items(), key=lambda p: p[1]) finds the podium without fully sorting a million rows.

Step 2

Try it yourself

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The lesson example is loaded and ready — press Run, then change something and run it again. Breaking it is part of learning. Want a clean slate? Tap “New blank”.

PYexample.py

⌘ + Enter to run

Output appears here…

Step 3

Pass the challenge +35 XP

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From units = {"laptop": 12, "mouse": 41, "monitor": 9, "keyboard": 25, "webcam": 17}, print the top 3 sellers as 1. mouse (41 sold), 2. keyboard (25 sold), 3. webcam (17 sold).

Target output

1. mouse (41 sold)
2. keyboard (25 sold)
3. webcam (17 sold)

PYchallenge.py

units = {"laptop": 12, "mouse": 41, "monitor": 9, "keyboard": 25, "webcam": 17}

top = sorted(units.items(), key=lambda pair: pair[1], reverse=True)[:3]
for rank, (product, sold) in enumerate(top, start=1):
    print(f"{rank}. {product} ({sold} sold)")

Run your code to check it…

Step 4

Check your understanding

1. What does max(units, key=units.get) return? The largest value The key with the largest value A (key, value) tuple An error

2. What does enumerate(top, start=1) add to the loop? Sorting A rank counter starting at 1 alongside each item Reversal Filtering

Last step

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