RecursionError: Maximum Recursion Depth Exceeded

Why This Happens

Python limits recursion depth to 1000 frames by default. When a recursive function lacks a proper base case or input is too large, the stack exceeds this limit.

The Problem

def factorial(n):
    return n * factorial(n - 1)

factorial(5)

The Fix

def factorial(n):
    if n <= 1:
        return 1
    return n * factorial(n - 1)

# Or iterative:
def factorial(n):
    result = 1
    for i in range(2, n + 1):
        result *= i
    return result

Step-by-Step Fix

1. 1

   Add a base case

   Every recursive function needs a stopping condition.

2. 2

   Verify base case is reachable

   Ensure recursive calls move toward the base case.

3. 3

   Convert to iteration

   Rewrite using a loop or use functools.lru_cache for memoization.