What is recursion?

A function calling itself is recursion.

Recursion is when a function calls itself. It solves a problem by breaking it into smaller instances of the same problem.

Every recursive function has two parts: a base case (stopping condition) and a recursive step (self-call).

Base case

The base case is the condition where recursion stops. Without it, the function calls itself forever and a stack overflow occurs.

The base case directly solves the smallest problem. For example, in countdown(0) the base case might be 'stop if 0'.

Write countdown(n). Print n, if n > 0 call countdown(n-1). Call countdown(3) to print 3, 2, 1.

Show example solution

def countdown(n):
    # Count down
    print(n)
    if n > 0:
        countdown(n - 1)
countdown(3)

Base case

The condition that stops recursion: ____

Show answer

The condition that stops recursion: base case

Next lesson: Base case