Groups > comp.lang.python > #20753

Re: sum() requires number, not simply add

References	<91c71e41-b98c-46f6-b3af-bed894cf9d92@kh11g2000pbb.googlegroups.com> <41177e2c-3cf7-4678-8594-5a81290eaa4d@ub4g2000pbc.googlegroups.com>
Date	2012-02-23 21:41 +0000
Subject	Re: sum() requires number, not simply __add__
From	Arnaud Delobelle <arnodel@gmail.com>
Newsgroups	comp.lang.python
Message-ID	<mailman.90.1330033290.3037.python-list@python.org> (permalink)

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On 23 February 2012 21:23, Buck Golemon <buck@yelp.com> wrote:
> def sum(values,
> base=0):
>      values =
> iter(values)
>
>      try:
>          result = values.next()
>      except StopIteration:
>          return base
>
>      for value in values:
>          result += value
>      return result

This is definitely not backward compatible.  To get something that has
a better chance of working with existing code, try this (untested):

_sentinel = object()

def sum(iterable, start=_sentinel):
    if start is _sentinel:
        iterable = iter(iterable)
        try:
            start = iterable.next()
        except StopIteration:
            return 0
    for x in iterable:
        start += x
    return start

del _sentinel

-- 
Arnaud

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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