[Tutor] Function returns 'None'

[Adam Bark]

On 11/07/10 14:59, Dominik Danter wrote:
> Hello
>
> As en exercise I wrote the following function:
>
>
> def recursfac(x,carryover=1):
>     print 'x:',x,'carryover:', carryover
>     if x > 1:
>         carryover *= x
>         recursfac(x-1, carryover)
>     else:
>         return carryover
>
> print recursfac(3)
>
> Very much to my surprise I get the following output:
>
> x: 3 carryover: 1
> x: 2 carryover: 3
> x: 1 carryover: 6
> None
>
> Where did I go wrong?
>
> Kind regards
> Dominik Danter

I made a diagram to try to explain

recursfac(3)
     recursfac(2, 3) <----|
         recursfac(1, 6)  _|

As you can see recursfac(1,6) returns it's value (carryover) to 
recursfac(2, 3) which ignores it and completes it's execution ie 
returning None to your original call which then prints out that return 
value.
I hope that's clear.

Adam.