Question

In Python

Use the Design Recipe to write a function factorial that when given a positive integer calculates the factorial. If given a negative integer or not an integer), the function should return None. If given 0, it should return 1.

Include a docstring!

Note: You may assume all arguments passed to this function will be numeric.

Write three assertEqual statements to test your function. To test and receive credit for your assertEqual statements, copy them into Part E and click 'Evaluate'.

Answer 1

def factorial(n):
    """
    if n is negative, then return None
    if n is zero, then return 1
    if n is positive, then return factorial of n
    :param n:
    :return: factorial of number n
    """
    if n < 0:
        return None
    elif n == 0:
        return 1
    else:
        return n * factorial(n-1)


assert factorial(5) == 120
assert factorial(0) == 1
assert factorial(-2) is None