Factorial!
Get the factorial of a given number. Using sys.argv, pass in a number and return it's factorial.
To calculate the factorial of 5, for example, the equation is 5 * 4 * 3 * 2 * 1 = 120
Iterative
Write the equation iteratively, using a for or while loop. How to use loops in Python is well documented here
Bonus
Write this function recursively. If you run into difficulty, think about how your stack will develop as your function recurses and remember to define your base case.
Write assert statements to test your code in both cases.