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Re: Simple recursive sum function | what's the cause of the weird behaviour?

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On 7/6/2013 8:37 AM, Russel Walker wrote:
> I know this is simple but I've been starring at it for half an hour and trying all sorts of things in the interpreter but I just can't see where it's wrong.
>
> def supersum(sequence, start=0):
>      result = start
>      for item in sequence:
>          try:
>              result += supersum(item, start)
>          except:

Bare except statements cover up too many sins. I and others *strongly* 
recommend that you only catch what you *know* you actually want to (see 
below).

>              result += item
>      return result

I recommend that you start with at least one test case, and with an edge 
case at that. If you cannot bring yourself to do it before writing a 
draft of the function code, do it immediately after and run. If you do 
not want to use a framework, use assert.

assert supersum([]) == 0
assert supersum([], []) == []

Do the asserts match your intention? The tests amount to a specification 
by example. Any 'kind' of input that is not tested is not guaranteed to 
work.

Back to the except clause: only add try..except xxx when needed to pass 
a test.

-- 
Terry Jan Reedy

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Simple recursive sum function | what's the cause of the weird behaviour? Russel Walker <russ.pobox@gmail.com> - 2013-07-06 05:37 -0700
  Re: Simple recursive sum function | what's the cause of the weird behaviour? Russel Walker <russ.pobox@gmail.com> - 2013-07-06 05:54 -0700
  Re: Simple recursive sum function | what's the cause of the weird behaviour? Russel Walker <russ.pobox@gmail.com> - 2013-07-06 05:59 -0700
    Re: Simple recursive sum function | what's the cause of the weird behaviour? Peter Otten <__peter__@web.de> - 2013-07-06 15:19 +0200
    Re: Simple recursive sum function | what's the cause of the weird behaviour? Joshua Landau <joshua.landau.ws@gmail.com> - 2013-07-06 19:43 +0100
      Re: Simple recursive sum function | what's the cause of the weird behaviour? Rotwang <sg552@hotmail.co.uk> - 2013-07-06 21:10 +0100
        Re: Simple recursive sum function | what's the cause of the weird behaviour? Rotwang <sg552@hotmail.co.uk> - 2013-07-06 21:25 +0100
  Re: Simple recursive sum function | what's the cause of the weird behaviour? Chris Angelico <rosuav@gmail.com> - 2013-07-07 03:22 +1000
  Re: Simple recursive sum function | what's the cause of the weird behaviour? Terry Reedy <tjreedy@udel.edu> - 2013-07-06 14:47 -0400
  Re: Simple recursive sum function | what's the cause of the weird behaviour? Russel Walker <russ.pobox@gmail.com> - 2013-07-07 09:13 -0700
  Re: Simple recursive sum function | what's the cause of the weird behaviour? Russel Walker <russ.pobox@gmail.com> - 2013-07-07 09:44 -0700

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