#!/usr/bin/python

"""
    functions.py -- defining and using a function

    Jeff Ondich, 24 October 2006

    Read, predict the output, experiment.
"""

def factorial(n):
    if n < 0:
        raise ValueError, "You can't take the factorial of a negative integer."
        return 0

    if n <= 1:
        return 1

    return n * factorial(n - 1)


print factorial(6)
print factorial(0)
print factorial(1)
print

print "What usually happens in Java when you compute the factorial of 20?"
print factorial(20)
print

print "Let's try a negative number"
print factorial(-5)