Comprehensions
A comprehension builds a new collection from an old one in one expression: [n * 2 for n in numbers if n > 0]. Read it as “for each, if, do this”.
Python for Kids · Class 9 · Module 2 of 9
Advanced Collections
Five lines of loop, or one line that says exactly the same thing.
8 sessionsSessions 9–16
4 weeksTypical pace
Intermediate to AppliedLevel
Class 9Python & Coding
The big idea
Comprehensions let students express filtering and transforming as a single readable expression. Combined with confident handling of nested data, this is the toolkit for reshaping real-world information.
Why it matters
Data arrives in the wrong shape almost always. Reshaping it quickly and correctly is the everyday work of anyone who codes with data.
Unpacked
What you will actually learn
Three core ideas, each taught with worked examples and then practised until it feels obvious.
Nested data
Nested data needs careful traversal — a list of dictionaries each containing a list. Naming loop variables honestly prevents most confusion.
Transformations
Transformations convert between shapes: list to dictionary, grouped by category, filtered and sorted. This is the core of data preparation.
Did you know?
Comprehension syntax comes from set-builder notation in mathematics: {x² | x ∈ N, x < 10} translates almost directly into Python.
Common mix-up
“Shorter is always better.” A comprehension four levels deep is worse than a plain loop. Clarity wins over compression.
Session by session
Your 8-session journey
Sessions 9–16 of the 72-session year, at two one-hour sessions per week.
- 1
Warm-up and big picture
Where this module fits, what you will build, and a hands-on starter that gets everyone curious about comprehensions.
- 2
Comprehensions
Guided teaching on comprehensions, worked through together with the teacher.
- 3
Comprehensions — practice lab
Independent practice, small challenges and one deliberate mistake to diagnose.
- 4
Nested data
Guided teaching on nested data, building directly on the previous two sessions.
- 5
Nested data — practice lab
Applied tasks that combine comprehensions and nested data in one piece of work.
- 6
Transformations
Transformations introduced and practised, completing the toolkit needed for the project.
- 7
Project build
Guided build session for the module project: Data-cleaning challenge.
- 8
Test, present and reflect
Finish, test against the checklist, present the work and explain the decisions behind it.
Project lab
Data-cleaning challenge
Every module ends with something the student built themselves and can demonstrate. This is the piece that goes into their portfolio and gets explained out loud at the end of session 16.
Try this at home
Take a messy dataset and clean it using only comprehensions, then rewrite the same work as loops and decide honestly which reads better.
It is finished when
- It works from start to finish without breaking
- You can explain every part of it in your own words
- You tested it and improved at least one thing afterwards
- Someone else used or understood it without your help
By the end of this module
Students finishing Module 2 can:
- Explain and use comprehensions without prompting
- Explain and use nested data without prompting
- Explain and use transformations without prompting
- Build and finish data-cleaning challenge
- Test your own work and correct what you find
- Talk an adult through what you made and why
Word bank
The vocabulary introduced here, in plain language:
- comprehension
- A compact expression that builds a collection.
- transformation
- Converting data from one shape to another.
- filter
- Keeping only the items that meet a condition.
Module challenge
Think you have got this?
0 XPLevel 1 · Curious Beginner
6 quick questions drawn from this module — vocabulary, the project you build, and a myth-or-fact round. Every wrong answer explains itself, so a mistake still teaches you something.
Your child's free trial is one message away.
Tell us your child’s class and what they enjoy. We will suggest the closest program fit—no pressure and no upfront payment.