Sorting and Comparing Checkpoint

Optional

22 min · Intermediate

A review of this module. Skip it if you feel confident; the next module does not need it.

Fix the mistakes

The slips that cost marks in this module. Spot each one, then check the fix.

This checkpoint mixes everything from the module on data like customer orders, marks and staff records. Decide first which tool fits, then write it.

Rank with sorted, key and reverse

Ranking is ordering records by a score, usually highest first, with a second field to break ties. In Python it is sorted with a tuple key.

A leaderboard lists customers by total spend, highest first, and breaks ties by name. One key and one sorted call do it.

Python

spend = {"Asha": 370, "Ravi": 400, "Meena": 400, "Diya": 50}ranked = sorted(spend.items(), key=lambda pair: (-pair[1], pair[0]))for place, (name, total) in enumerate(ranked, start=1):    print(place, name, total)

Example 1 · Top three earners

Python

from operator import itemgetter
pay = [("Asha", 52000), ("Ravi", 61000), ("Meena", 47000), ("Kiran", 58000)]top = sorted(pay, key=itemgetter(1), reverse=True)[:3]print(top)

Output

[('Ravi', 61000), ('Kiran', 58000), ('Asha', 52000)]

What this code does

itemgetter(1) sorts by pay and reverse=True puts the highest first.
The slice keeps the first three.

The key (-total, name) sorts highest total first and then alphabetically on a tie.

Pick the right tool

Do you need the whole order, one extreme, or a position? The answer decides between sorted, min or max, and bisect.

Python

1from bisect import bisect_right2
3amounts = [250, 40, 900, 120]4print(sorted(amounts))5print(max(amounts), min(amounts))6print(bisect_right(sorted(amounts), 200))

Example 2 · Grade bands

Python

from bisect import bisect_right
cutoffs = [40, 60, 75, 90]print([ "FDCBA"[bisect_right(cutoffs, m)] for m in [95, 82, 67, 45, 30]])

Output

['A', 'B', 'C', 'D', 'F']

What this code does

Each mark is placed among the cutoffs and the position picks the letter.
A mark equal to a cutoff, such as 75, lands in the higher band.

sorted gives the full order, max and min scan once, and bisect needs a list that is already sorted.

Make your own objects sortable

A support team works on tickets by priority, then by title. A dataclass with order=True gives that order for free.

Python

1from dataclasses import dataclass2
3
4@dataclass(order=True)5class Ticket:6    priority: int7    title: str8
9
10queue = [Ticket(2, "Login"), Ticket(1, "Refund"), Ticket(2, "Export")]11print(min(queue))12print([t.title for t in sorted(queue)])

Example 3 · Department report

Python

staff = [("Asha", "Sales", 52000), ("Ravi", "IT", 61000), ("Meena", "Sales", 47000), ("Kiran", "IT", 58000)]for name, dept, pay in sorted(staff, key=lambda s: (s[1], -s[2])):    print(dept, name, pay)

Output

IT Ravi 61000
IT Kiran 58000
Sales Asha 52000
Sales Meena 47000

What this code does

The key sorts by department and then by pay from highest to lowest.
Tuple unpacking in the loop gives readable names.

min and sorted both use the order that order=True generated.

Module quiz

Questions from the whole module. Your first answer is your score.

Problems

Graded easy to hard, using everything from this module.

Try each one yourself first. Use the hint if you get stuck. Mark it as done when it works.

Exercise 1· Easy

Print marks = [72, 95, 88, 60, 95] from highest to lowest as a list, without changing the original list.

Expected output

[95, 95, 88, 72, 60]

Exercise 2· Easy

prices = [("Keyboard", 45), ("Monitor", 210), ("Cable", 8)]. Print the name of the cheapest product, then of the most expensive.

Expected output

Cable
Monitor

Exercise 3· Medium

staff = [("Asha", "Sales", 52000), ("Ravi", "IT", 61000), ("Meena", "Sales", 47000), ("Kiran", "IT", 58000)]. Print lines like IT Ravi 61000, ordered by department, then pay from highest to lowest.

Expected output

IT Ravi 61000
IT Kiran 58000
Sales Asha 52000
Sales Meena 47000

Exercise 4· Medium

Create @dataclass(order=True) class Ticket with priority (int) and title (str). Sort Ticket(3, "Export"), Ticket(1, "Refund"), Ticket(3, "Login") and print the titles as a list.

Expected output

['Refund', 'Export', 'Login']

Exercise 5· Medium

Cutoffs are [40, 60, 75, 90], grades "FDCBA". Write grade(mark) using bisect_right and print grade(75), grade(74) and grade(100) on separate lines.

Expected output

B
C
A

Exercise 6· Hard

Orders: [("Asha", 250), ("Ravi", 90), ("Asha", 120), ("Meena", 400), ("Ravi", 310), ("Diya", 50)]. Add up the total per customer, then print the top three customers, highest total first and alphabetical on a tie, as Meena 400.

Expected output

Meena 400
Ravi 400
Asha 370

Exercise 7· Hard

Write EventLog that keeps timestamps sorted with insort. count_between(low, high) returns how many timestamps lie between low and high inclusive. Add 50, 10, 30, 20, 40 and print count_between(15, 40) and count_between(0, 10).

Expected output

3
1

Exercise 8· Hard

Marks: {"Asha": 95, "Ravi": 88, "Meena": 95, "Diya": 70, "Kiran": 88}. Print rank name mark per student, highest mark first, alphabetical on a tie. Students with the same mark share a rank, and the next rank skips ahead (1, 1, 3, 3, 5).

Expected output

1 Asha 95
1 Meena 95
3 Kiran 88
3 Ravi 88
5 Diya 70

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Questions interviewers ask on this topic.

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Next: Double-Ended Queues with collections.deque

spend = {"Asha": 370, "Ravi": 400, "Meena": 400, "Diya": 50}ranked = sorted(spend.items(), key=lambda pair: (-pair[1], pair[0]))for place, (name, total) in enumerate(ranked, start=1): print(place, name, total)

1from dataclasses import dataclass2 3 4@dataclass(order=True)5class Ticket:6 priority: int7 title: str8 9 10queue = [Ticket(2, "Login"), Ticket(1, "Refund"), Ticket(2, "Export")]11print(min(queue))12print([t.title for t in sorted(queue)])

staff = [("Asha", "Sales", 52000), ("Ravi", "IT", 61000), ("Meena", "Sales", 47000), ("Kiran", "IT", 58000)]for name, dept, pay in sorted(staff, key=lambda s: (s[1], -s[2])): print(dept, name, pay)

Rank with sorted, key and reverse

What this code does

Pick the right tool

What this code does

Make your own objects sortable

What this code does

Exercise 1· Easy

Exercise 2· Easy

Exercise 3· Medium

Exercise 4· Medium

Exercise 5· Medium

Exercise 6· Hard

Exercise 7· Hard

Exercise 8· Hard

You finished the preview of Sorting & Comparing

Rank with sorted, key and reverse

What this code does

Pick the right tool

What this code does

Make your own objects sortable

What this code does

A function receives a list it must not change and needs it sorted. Which fits best?

What does this print?

What does key=lambda s: (-s[1], s[0]) do?

You need only the largest order amount from a big list. Which is best?

A list of dictionaries must be sorted by the "pay" key. Which key works?

A list of Employee objects must be sorted by the name attribute. Which key works?

In @dataclass(order=True), which field is compared first?

What error does sorting instances of a plain class with no __lt__ raise?

What does bisect_right([10, 20, 20, 30], 20) return?

What does sorted(["banana", "Apple", "cherry"]) return?

What happens with sorted([3, None, 1])?

To sort department ascending and name descending (both text), you should:

Exercise 1· Easy

Exercise 2· Easy

Exercise 3· Medium

Exercise 4· Medium

Exercise 5· Medium

Exercise 6· Hard

Exercise 7· Hard

Exercise 8· Hard

Q1A list of dictionaries must be sorted by department ascending and pay descending. How?

Q2Why does stability matter for multi-pass sorting?

Q3sorted(items)[0] or min(items)?

Q4How would you keep a leaderboard sorted while scores arrive?

Q5When do you define __lt__ and when do you pass key?

You finished the preview of Sorting & Comparing

A function receives a list it must not change and needs it sorted. Which fits best?

What does this print?

What does key=lambda s: (-s[1], s[0]) do?

You need only the largest order amount from a big list. Which is best?

A list of dictionaries must be sorted by the "pay" key. Which key works?

A list of Employee objects must be sorted by the name attribute. Which key works?

In @dataclass(order=True), which field is compared first?

What error does sorting instances of a plain class with no __lt__ raise?

What does bisect_right([10, 20, 20, 30], 20) return?

What does sorted(["banana", "Apple", "cherry"]) return?

What happens with sorted([3, None, 1])?

To sort department ascending and name descending (both text), you should:

Q1A list of dictionaries must be sorted by department ascending and pay descending. How?

Q2Why does stability matter for multi-pass sorting?

Q3sorted(items)[0] or min(items)?

Q4How would you keep a leaderboard sorted while scores arrive?

Q5When do you define __lt__ and when do you pass key?

What does `key=lambda s: (-s[1], s[0])` do?

What error does sorting instances of a plain class with no lt raise?

What does `bisect_right([10, 20, 20, 30], 20)` return?

What does `sorted(["banana", "Apple", "cherry"])` return?

What happens with `sorted([3, None, 1])`?

What does `key=lambda s: (-s[1], s[0])` do?

What error does sorting instances of a plain class with no lt raise?

What does `bisect_right([10, 20, 20, 30], 20)` return?

What does `sorted(["banana", "Apple", "cherry"])` return?

What happens with `sorted([3, None, 1])`?