Recursive Functions - Factorial-CodePudding

I am totally new to recursive functions and tried to create a function to compute the factorial of n. In my example I assume n > 0.

def myfactorial(n):
    if (n - 1) > 0:                       # Check if n - 1 is > 0
       return ( n * myfactorial(n - 1) )  # Then multiply current n with myfactorial(n - 1)
    else:
        return                            # If condition is false, then stop function

However, it the error unsupported operand type(s) for *: 'int' and 'NoneType' for the line return ( n * myfactorial(n - 1) ).

When looking at the solution from w3resource.com

def factorial(n):
    if n == 0:
        return 1
    else:
        return n * factorial(n - 1)

They use the same return idea in the statement as I.

Can anyone tell me what is wrong in my approach (by the way, I designed the if statement on purpose as n-1 > 0, nevertheless it has to work with this statement as well)?

Many thanks for your help!

CodePudding user response：

When you write return it's have the same effect as return None.

When you do myfactorial(1), you return None. With myfactorial(2), you do 2 * myfactorial(1), which is equivalent to 2 * None, which trigger the error :

unsupported operand type(s) for *: 'int' and 'NoneType'

That why you have to write return 1 in your else branch.