Recursion

"""
The simplest possible example of recursion in Python is the calculation of the factorial of a number.

This simple example demonstrates the basic concept of recursion: a function calling itself to solve a smaller instance of the same problem, with a base case to terminate the recursion.
"""
def factorial(n):
    # Base case: if n is 0, return 1
    if n == 0:
        return 1
    # Recursive case: n * factorial of (n-1)
    else:
        return n * factorial(n-1)

# Example usage
print(factorial(5))  # Output: 120