Recursion code not working as expected - Python 3

Question

I am a beginner to programming and in this case cannot understand why this Python code doesn't work as expected.

I am trying to use recursion by calling a function within a function; calling the function n times, and reducing n by 1 to 0 with each loop at which point it will stop.

Instead my code prints 'freak' once, then I get a 'maximum recursion depth' error message.

def print_m():
    print ('freak')

def do_n(arg, n)):
    if n >= 0:
        print (do_n(arg,n))
        n = n - 1

You need to decrement n BEFORE your recursive call.

polku
– polku

2016-08-31 14:38:54 +00:00
Commented Aug 31, 2016 at 14:38 — polku
– polku, Commented Aug 31, 2016 at 14:38

ForceBru · Accepted Answer · 2016-08-31 14:39:48Z

7

Recursion is not a loop!

You should be passing n - 1 to the recursive call instead of merely n, not subtracting one from n after this call.

answered Aug 31, 2016 at 14:39

ForceBru

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2 Comments

Katy Over a year ago

This solved it, thank you, though I the output is 'None' for all calls other than the initial one, which I don't understand. I'll go back to the text book and play around a bit more!

ForceBru Over a year ago

@Katy, it should be None as you're calling the function do_n recursively and printing the returned value. This function doesn't return anything, so you're getting a None.

ForceBru · Accepted Answer · 2016-08-31 14:43:50Z

1

Passing n-1 as parameter to recursive call fixes the problem.

edited Aug 31, 2016 at 14:43

ForceBru

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answered Aug 31, 2016 at 14:43

Andriy Ivaneyko

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Comments

user3500741 · Accepted Answer · 2016-09-02 11:55:43Z

0

In the recursive call in line 6 you should pass print (do_n(arg,n-1)) .

answered Sep 2, 2016 at 11:55

user3500741

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