Function returning None instead of expected string

Question

I am trying to simulate a very simple text editor that accepts lines of text from the user, combines the text into a single string and then prints the string to a file. When I ran my code I discovered that the file contents were simply 'None'.

I traced the code and found that the resultant string being returned from the core function getpayload() is 'None' although the string is built properly right up until the point of return.

The code (stripped of file I/O executed as is):

def getpayload(s):
        temp = getln()
        if temp.upper() != "END":
            s += temp
            getpayload(s)
        else:
            return s

def getln():
    txt = input("|> ")
    return str(txt)

def start():
    text = getpayload("")
    print(text)


if __name__ == "__main__":
    start()

When run the following is produced:

$ python3.2 editor.py
|> Line one
|> Line two
|> Line three
|> 
|> Line five
|> END
$ None

Printing the string in the else statement produces output of the string as expected. I have also enclosed the return string in str().

I have researched other methods of producing the desired output but I am new to python and I am interested in learning why this sort of issue would occur.

possible duplicate of [Weird function return value?](http://stackoverflow.com/questions/11097822/weird-function-return-value) — Ashwini Chaudhary, Sep 25 '13 at 15:32

Rohit Jain · Accepted Answer · 2013-09-25T15:37:20.570

8

You are not returning the result of the recursive function call. These issues are often overlooked by beginners, when you are returning from a recursive functions. Change the if block in your first function to:

if temp.upper() != "END":
    s += temp
    return getpayload(s)

If you don't add return, then the value returned from return s is simply discarded, and your function by default returns None.

edited Sep 25 '13 at 15:37

answered Sep 25 '13 at 15:32

Rohit Jain

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score 0 · Answer 2 · answered Sep 25 '13 at 15:32

0

When recursing, you need to return the value else you drop it:

if temp.upper() != "END":
   s += temp
   return getpayload(s)

answered Sep 25 '13 at 15:32

unwind

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Function returning None instead of expected string

2 Answers2