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Lesson 6 — Recursion: factorial
Recursion: a function that calls itself
Recursion solves a problem by solving a smaller version of the same problem. It needs two parts: a base case that answers directly (so it stops), and a recursive case that calls the function on a smaller input. Factorial is the classic: 5! = 5 × 4 × 3 × 2 × 1, which is 5 × 4!.
# fact(3) = 3 * fact(2) = 3 * 2 * fact(1) = 3 * 2 * 1 = 6
Watch out: forget the base case and the function calls itself forever until Python stops it with a RecursionError.
Why it matters: trees, folders and many "divide and conquer" algorithms are naturally recursive.
Want it another way?
Task
Write the recursive case: return n times fact(n - 1). Expected: factorials of 1 to 5.
Run your code — when the output matches the task, you will see a green check. Then mark the lesson complete.
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