Python: My return variable is always None

Question

So I found a strange thing that happens in python whenever I try to return an optional parameter or at least I think that is why it is happening.

Here is my code

def reverse(string, output = ""):
    if string == "":
        print "winner: ", output
        return output
    output = output + string[-1]
    string = string[:-1]
    reverse(string, output=output)

And here is what happens when I run it:

>>> output = reverse("hello")
winner:  olleh
>>> print output
None

Anyone know why my return is always None?

Your function has no return value for anything other than the input "" — Cory Kramer
– Cory Kramer, Commented Aug 12, 2015 at 23:31

chepner · Accepted Answer · 2015-08-12 23:31:33Z

2

You have to return the return value of the recursive call.

def reverse(string, output = ""):
    if string == "":
        print "winner: ", output
        return output
    output = output + string[-1]
    string = string[:-1]
    return reverse(string, output=output)

answered Aug 12, 2015 at 23:31

chepner

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1 Comment

still learning Over a year ago

Ahh I didn't think about having to go back out of my recursion with the return statement. It makes sense though. Thanks.

Maddy · Accepted Answer · 2015-08-12 23:33:07Z

0

def reverse(string, output = ""):
    if string == "":
        print ("winner: ", output)
        return output
    output = output + string[-1]
    string = string[:-1]
    return reverse(string, output=output)
def main():
    reverse("hello")
main()

OR

def reverse(string, output = ""):
    if string == "":
        print ("winner: ", output)
        return output
    output = output + string[-1]
    string = string[:-1]
    return reverse(string, output=output)
reverse("hello")

OUTPUT FOR BOTH

>>> 
winner:  olleh
>>> ================================ RESTART ================================
>>> 
winner:  olleh
>>>

answered Aug 12, 2015 at 23:33

Maddy

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