Python lesson 18: Looping through lists
UK version. UK school years and UK spelling. · US version of this lesson
for x in nums: gives each item in turn – no index needed. A complete 40-minute Python lesson for complete beginners (Year 7, KS3), from Unit 5: Lists. It runs right here in your browser – nothing to install.
- Time
- 40 minutes + 20 min homework
- Year
- Year 7, KS3 (ages 11–12)
- You need
- A computer or tablet, paper and a pencil
- Marked
- Instantly, with explanations
For parents: how to use this lesson
You don't need to know Python yourself. The lesson explains each step on screen, the way Mr Babbage, our Head of Computing, likes it: a worked example first, then a go for your child. Code questions run your child's program in the browser and mark it straight away.
- Read what your child will learn together.
- Press Start the lesson below. Sit with your child for the teaching and the worked example (about 16 minutes): ask them to say what each line does.
- Let them do the practice on their own. When code goes wrong, the error message is a clue – let them read it out and try again before you help.
- Finish with the exit questions and the talk question: “How would you find the smallest item instead?”
- Later that day or the next day: the homework (20 minutes), then a practice test.
Watch out for
- Start the biggest at 0. Try a list of negative numbers.
- x is the index. Print x inside the loop: it is the item.
Miss Lovelace's tip for home: ask your child to explain one line of their program to you in their own words. If they can explain it, they understand it – and every error message is a clue, not a failure.
What your child will learn
We are learning to loop through every item of a list.
Success looks like
- I can loop through every item of a list.
- I can total and count items in a list.
- I can find the biggest item with a loop.
Key words
iterate · total · maximum · algorithm
What to have ready
- A device with a web browser (the code runs in the browser – nothing to install)
- Paper for tracing
- A keyboard helps for typing code (a tablet or phone works too)
The big ideas (for the adult)
for x in nums: gives each item in turn – no index needed.
To total a list, start with total = 0 and add each item inside the loop.
To find the biggest, start with the FIRST item (not 0) and replace it whenever you find a bigger one – that works for negative numbers too.
Worked example
for x in ["Uranus", "Venus", "Mercury"]:
print(x)It prints:
Uranus Venus Mercury
The lesson, step by step
| Part | Time | How it is checked |
|---|---|---|
| Starter | 5 min | Marked by Classfern |
| Teaching input | 8 min | Read, watch and talk |
| See it, then predict | 8 min | Marked by Classfern |
| Put it in order, write it, fix it | 14 min | Marked by Classfern |
| Plenary and exit ticket | 5 min | Marked by Classfern + self-check |
The lesson
It runs here on the page. No sign-up and no names – progress is kept only in this browser. Each visit picks a new mix of questions.
Homework
20 minutes: 7 questions – predict what code prints, write or fix a short program, and check the key ideas – then a short reflection. New questions every time, all marked instantly.
Practice tests
Curriculum
National curriculum in England, computing, key stage 3: pupils should be taught to use 2 or more programming languages, at least one of which is textual, to solve a variety of computational problems; make appropriate use of data structures [for example, lists, tables or arrays]; design and develop modular programs that use procedures or functions; and to understand several key algorithms that reflect computational thinking [for example, ones for sorting and searching]; use logical reasoning to compare the utility of alternative algorithms for the same problem.
Contains public sector information licensed under the Open Government Licence v3.0.
Our lessons and questions are our own. They are not written or endorsed by any government department, testing agency or exam board. Python is a registered trademark of the Python Software Foundation; Classfern is not affiliated with or endorsed by it.