Python: Recursion only one output

Question

I wanted to write a recursive function to fit curves. For some reasons my results didn't looked good so I boiled down the problem to one easy example:

Number = 6
Successor = 0

def Fuction(Number, Successor):
    if (Number - Successor)+1>0:
       Successor += 1
       Fuction(Number, Successor)
    else:
        return(Fuction(Number, Successor))


A = Fuction(Number, Successor) 
print(f'The Successor of {Number} is {A}')

When I do this the Kernel dies. How can I fix it? (I followed the awnser : Why does my recursive function return none)

"The kernel dies" -- yikes! Are you sure this isn't just the CPython interpreter gently raising an error? What output are you expecting here and why use recursion at all? — ggorlen, Jun 02 '21 at 15:17
Why are you calling `Fuction()` again in the `if (Number - Successor) + 1 > 0` branch? When do you expect this function to _stop recurring_, and what is it supposed to return in that branch? — Green Cloak Guy, Jun 02 '21 at 15:17
I expect this function to stop recurring if "Successor = Number + 1". Again this is an abstract version of my real problem. I just want to know how I can use the return function such that the output reads: "The Successor of 6 is 7" — Phicalc, Jun 02 '21 at 15:21
I'm afraid to ask, but why not do 6 + 1? The problem here should be pretty clear by stepping with a debugger or adding a print. Your base case is supposed to be the `else` branch. "Base case" means "stop the recursion", yet you do `return(Fuction(Number, Successor))` in this branch, continuing the recursion infinitely. You can just `return Successor`, then your problem reduces to the link you provided because the recursive branch isn't returning anything. As an aside, only classes should start with uppercase letters. The convention is to use lower-case for vars. — ggorlen, Jun 02 '21 at 15:25
Again: This is an abstract version of my real problem. I want to create a recursive function to fit data (without using lmfit whatsoever). I want my output not just to be something I print but something I can use in my code later. When I return successor, I get the awnser 'none' when it's in the else block, or the awnser 'the successor of 6 is 1' — Phicalc, Jun 02 '21 at 15:40

score 1 · Accepted Answer · answered Jun 02 '21 at 15:33

Maybe something like this?

Number = 6
Successor = 0

def Fuction(Number, Successor):
    if (Number - Successor) + 1 == 0: # base case for interrupting recursion
        return Successor
    Successor += 1
    return Fuction(Number, Successor)

A = Fuction(Number, Successor) # will be 7
print(f'The Successor of {Number} is {A}')

You can also do it like this which is more similar to your code example:

def Fuction(Number, Successor):
    if (Number - Successor) + 1 > 0:
        Successor += 1
        return Fuction(Number, Successor)
    return Successor

score 0 · Answer 2 · edited Jun 02 '21 at 16:02

The problem here is that the recursion does not terminate. The issue occurs when Number=6 and Successor=7, Fuction(6,7) just calls Fuction(6,7) again and again until the interpreter crashes due its recursion limit being exceeded. I believe this is when your kernel dies.

The solution here is to find the right base case for the recursion where it can return without making another recursive call.

Here's a nice video explaining how to implement recursion.

Python: Recursion only one output

2 Answers2