Py Recursion — Free Python Tutorial

TL;DR: Learn Py Recursion in Python with a free, beginner-friendly tutorial, examples and practice for Indian students on Syllab.in.

Py Recursion in Python

Recursion is a programming technique where a function solves a problem by calling itself with a smaller version of the same problem. The key insight: "if I can solve a small version, I can solve any size."

Every recursive function needs two parts: Base Case (when to stop — prevents infinite recursion), Recursive Case (the function calling itself with a simpler input, moving toward the base case).

Classic recursion examples: Factorial (n! = n × (n-1)!), Fibonacci sequence, Tower of Hanoi, binary search, tree traversal, directory listing. Recursion is elegant for problems that have natural self-similar structure.

Recursion vs Iteration: Recursion is often cleaner code but uses more memory (each call uses stack space). Python has a recursion limit (~1000 calls deep). For very deep recursion, convert to iteration. For simple cases, recursion is fine.

def factorial(n):
    if n == 0:        # BASE CASE
        return 1
    return n * factorial(n - 1)  # RECURSIVE CASE

# Call stack for factorial(4):
# factorial(4) → 4 * factorial(3)
# factorial(3) → 3 * factorial(2)
# factorial(2) → 2 * factorial(1)
# factorial(1) → 1 * factorial(0)
# factorial(0) → 1  ← BASE CASE

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