Groups > comp.lang.python > #20758

Re: sum() requires number, not simply add

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From	Ian Kelly <ian.g.kelly@gmail.com>
Date	2012-02-23 15:00 -0700
Subject	Re: sum() requires number, not simply __add__
Newsgroups	comp.lang.python
Message-ID	<mailman.95.1330034439.3037.python-list@python.org> (permalink)

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On Thu, Feb 23, 2012 at 2:53 PM, Chris Angelico <rosuav@gmail.com> wrote:
> On Fri, Feb 24, 2012 at 8:41 AM, Arnaud Delobelle <arnodel@gmail.com> wrote:
>> _sentinel = object()
>>
>> def sum(iterable, start=_sentinel):
>>    if start is _sentinel:
>>
>> del _sentinel
>
> Somewhat off-topic: Doesn't the if statement there do a lookup for a
> global, which would mean that 'del _sentinel' will cause it to fail?
> Or have I missed something here?

I believe you're correct.  If you really want to delete the _sentinel
reference though, you could do:

def sum(iterable, start=object()):
    if start is sum.func_defaults[0]:
        ...

Cheers,
Ian

Thread

sum() requires number, not simply __add__ Buck Golemon <buck@yelp.com> - 2012-02-23 13:19 -0800
  Re: sum() requires number, not simply __add__ Buck Golemon <buck@yelp.com> - 2012-02-23 13:23 -0800
    Re: sum() requires number, not simply __add__ Arnaud Delobelle <arnodel@gmail.com> - 2012-02-23 21:41 +0000
    Re: sum() requires number, not simply __add__ Chris Angelico <rosuav@gmail.com> - 2012-02-24 08:53 +1100
      Re: sum() requires number, not simply __add__ Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-02-23 23:33 +0000
        Re: sum() requires number, not simply __add__ Chris Angelico <rosuav@gmail.com> - 2012-02-24 10:39 +1100
        Re: sum() requires number, not simply __add__ Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2012-02-24 12:41 +0100
          Re: sum() requires number, not simply __add__ Roy Smith <roy@panix.com> - 2012-02-24 08:23 -0500
            Re: sum() requires number, not simply __add__ Terry Reedy <tjreedy@udel.edu> - 2012-02-24 16:58 -0500
    Re: sum() requires number, not simply __add__ Arnaud Delobelle <arnodel@gmail.com> - 2012-02-23 21:59 +0000
    Re: sum() requires number, not simply __add__ Ian Kelly <ian.g.kelly@gmail.com> - 2012-02-23 15:00 -0700
    Re: sum() requires number, not simply __add__ Chris Angelico <rosuav@gmail.com> - 2012-02-24 09:04 +1100
    Re: sum() requires number, not simply __add__ Arnaud Delobelle <arnodel@gmail.com> - 2012-02-23 22:09 +0000
  Re: sum() requires number, not simply __add__ Arnaud Delobelle <arnodel@gmail.com> - 2012-02-23 21:32 +0000
  Re: sum() requires number, not simply __add__ Chris Rebert <clp2@rebertia.com> - 2012-02-23 13:32 -0800
    Re: sum() requires number, not simply __add__ Buck Golemon <buck@yelp.com> - 2012-02-23 13:38 -0800
      Re: sum() requires number, not simply __add__ Ian Kelly <ian.g.kelly@gmail.com> - 2012-02-23 14:54 -0700
  Re: sum() requires number, not simply __add__ Stefan Behnel <stefan_ml@behnel.de> - 2012-02-23 22:42 +0100
    Re: sum() requires number, not simply __add__ Duncan Booth <duncan.booth@invalid.invalid> - 2012-02-24 11:40 +0000
  Re: sum() requires number, not simply __add__ Peter Otten <__peter__@web.de> - 2012-02-24 09:29 +0100

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