A recursive function is a function that calls itself.

Recursion is useful for problems that can be broken into smaller versions of the same problem.

def factorial(n):
    if n == 0:
        return 1
    return n * factorial(n - 1)

• Shorter code
• Cleaner logic for some problems
• Useful for factorial, tree traversal, and divide-and-conquer problems

Every recursive function must have a base case, or it may keep calling itself forever.