data-structures/algorithms/recursion/factorial.py

def factorial(number):
    """
    Calculates the factorial of a number using recursion.
    """
    assert int(number) == number, "Factorial of decimals not possibe"

    if number < 0:
        raise ValueError("Factorial of a negative number not possible")

    if number in (0, 1):
        return 1
    else:
        return number * factorial(number - 1)


# Driver Code
if __name__ == "__main__":
    print(factorial(5))