Recursion
Functions that call themselves, and the base case that stops them.
Planned. This module is part of the plan and is not written yet.
Why it matters
To count the people in a queue, you could ask the person in front, 'How many are ahead of you?', and they ask the next, until the first person says 'Nobody'. That is recursion, and 'Nobody' is the base case.
Draft outline · in review- For
- Level 11–13 · SSS 2 to A level / JUPEB / foundation year
- Inside
- 5 lessons and a test · about 90 minutes
- Topic
- Python functions · extension, 3 of 4
Inside the module.
5 lessons in order, about 90 minutes in all, then a short test. Learners go at their own pace; the minutes are a guide, not a timetable.
Draft outline · in review
Lesson 1: A function that calls itself
Solve a problem by solving a smaller copy of it.
Explain15 min, from minute 0
Lesson 2: The base case
The simplest case, answered directly, which stops the calls.
Explain15 min, from minute 15
Lesson 3: Factorial, traced
Trace factorial(4) call by call, down and back up.
Worked example20 min, from minute 30
Lesson 4: Write your own
Write recursive countdowns, sums and powers.
Practice25 min, from minute 50
Lesson 5: When recursion goes wrong
Spot a missing base case and read Python's RecursionError.
Review15 min, from minute 75
End-of-module test
Write recursive functions with correct base cases and trace recursive calls step by step.
Mastered at 85% or more. Retake it until you pass; nothing is lost, and each try gives feedback.
Already know it? A Challenge Test (planned) clears the whole module: 90% overall, no objective below 75%.
Last stageafter about 90 min
Practicalities
Draft outline · in reviewBuilt to run offline
Planned to run on the Lantern's own computer, with no internet needed.
Languages
Planned first in English; every module aims to reach all of the Lantern's languages.
Try a question.
One question from the module, as a learner would meet it. Have a go, then open the worked solution a step at a time.
Draft outline · in review
What does this print? def countdown(n): if n == 0: print("Go!") else: print(n) countdown(n - 1) countdown(3)
Work it out on paper first, then show the answer and mark it yourself.
Particulars
Where it sits
What a learner can do after it
- Write a recursive function with a base case.
- Trace a recursive call step by step.
Needs first
Unlocks
Level
Level 11–13 · SSS 2 to A level / JUPEB / foundation year
Level mappings are approximate. A qualified teacher or lecturer in each country must check them before they appear in the app. Levels 13–18 describe the content, not the learner: “Level 15” means material usually taught in a second-year university course, whoever chooses to learn it.
Difficulty for its level
3 of 4 · Extension
Time
About 90 minutes
Alignments
- Aligned to PCAPpartial · in reviewPCAP: recursion (descriptive ref)
Alignment in review until a qualified teacher or lecturer checks it. No exam body, university or vendor endorses us; learners still sit the real exam. University-level modules give knowledge, not university credit.
Challenge Test
Planned: a Challenge Test to prove you know it and skip it. Pass at 90% overall, with no objective below 75%.
University courses it previews
Computer Science, Software Engineering
On these pathways
The route here.
Everything this module builds on, drawn as a route from its foundations. Solid lanes must be mastered first, or cleared by a Challenge Test; dashed lanes are suggestions that never lock anything.
- CO-BLK-SEQ-01 Instructions in order, Level 1–4, Coding. Planned.
- CO-BLK-SEQ-01Instructions in orderCoding · Primary 1 to Primary 4 (Level 1–4) · Planned
- CO-BLK-LOP-01 Repeat blocks, Level 3–5, Coding. Sample lesson in the demo.
- CO-BLK-LOP-01Repeat blocksCoding · Primary 3 to Primary 5 (Level 3–5) · Sample lesson in the demo Needs Instructions in order (required).Try the sample lesson: Repeat blocks
- DS-CMP-TYP-01 The home row, Level 3–6, Digital skills. Planned.
- DS-CMP-TYP-01The home rowDigital skills · Primary 3 to Primary 6 (Level 3–6) · Planned · recommended
- CO-BLK-CND-01 If this, then that, Level 3–6, Coding. Planned.
- CO-BLK-CND-01If this, then thatCoding · Primary 3 to Primary 6 (Level 3–6) · Planned · recommended
- CO-BLK-LOP-02 Patterns with loops, Level 4–6, Coding. Planned.
- CO-BLK-LOP-02Patterns with loopsCoding · Primary 4 to Primary 6 (Level 4–6) · Planned Needs Repeat blocks (required).
- MA-ARI-ORD-01 Order of operations, Level 5–6, Maths. Planned.
- MA-ARI-ORD-01Order of operationsMaths · Primary 5 to Primary 6 (Level 5–6) · Planned · recommended
- CO-BLK-LOP-03 Loops inside loops, Level 5–7, Coding. Planned.
- CO-BLK-LOP-03Loops inside loopsCoding · Primary 5 to JSS 1 (Level 5–7) · Planned · recommended
- CO-PRG-PYB-01Your first Python programCoding · JSS 1 to JSS 3 (BECE) (Level 7–9) · Planned Needs Patterns with loops (required), The home row (recommended).
- CO-PRG-PYB-02VariablesCoding · JSS 1 to JSS 3 (BECE) (Level 7–9) · Sample lesson in the demo Needs Your first Python program (required).Try the sample lesson: Variables
- CO-PRG-PYB-03Numbers and calculationsCoding · JSS 1 to JSS 3 (BECE) (Level 7–9) · Planned Needs Variables (required), Order of operations (recommended).
- MA-ALG-FRM-01Substituting into formulaeMaths · JSS 1 to JSS 2 (Level 7–8) · Planned · recommended
- CO-PRG-PYB-05Decisions with ifCoding · JSS 2 to SSS 1 (Level 8–10) · Planned Needs Numbers and calculations (required), If this, then that (recommended).
- CO-PRG-PYB-06Loops in PythonCoding · JSS 2 to SSS 1 (Level 8–10) · Planned Needs Decisions with if (required), Loops inside loops (recommended).
- CO-PRG-PYF-01Defining functionsCoding · JSS 2 to SSS 2 (Level 8–11) · Planned Needs Loops in Python (required).
- CO-PRG-PYF-02Parameters and return valuesCoding · JSS 3 (BECE) to SSS 2 (Level 9–11) · Planned Needs Defining functions (required), Substituting into formulae (recommended).
- CO-PRG-PYF-03ScopeCoding · JSS 3 (BECE) to SSS 2 (Level 9–11) · Planned Needs Parameters and return values (required).
- CO-PRG-PYF-05RecursionCoding · SSS 2 to A level / JUPEB / foundation year (Level 11–13) · Planned · the destination Needs Scope (required).
Help light the room where this is learned.
Every route on this map starts in a classroom with 24 stations, a tutor that works offline and a facilitator upstairs. Four are planned and waiting for light.