Factorial

Calculates the factorial of a number.

• Use recursion.
• If num is less than or equal to 1, return 1.
• Otherwise, return the product of num and the factorial of num - 1.
• Throws an exception if num is a negative or a floating point number.

def factorial(num):
  if not ((num >= 0) and (num % 1 == 0)):
    raise Exception("Number can't be floating point or negative.")
  return 1 if num == 0 else num * factorial(num - 1)

factorial(6) # 720