recursive factorial function

2 lines of code:

def fac(n):
    return 1 if (n < 1) else n * fac(n-1)

Test it:

print fac(4)

Result:

24

We can combine the two functions to this single recursive function:

def factorial(n):
   if n < 1:   # base case
       return 1
   else:
       returnNumber = n * factorial(n - 1)  # recursive call
       print(str(n) + '! = ' + str(returnNumber))
       return returnNumber