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Re: sum() requires number, not simply __add__

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On Thu, Feb 23, 2012 at 2:38 PM, Buck Golemon <buck@yelp.com> wrote:
> My proposal is still *slightly* superior in two ways:
>
> 1) It reduces the number of __add__ operations by one
> 2) The second argument isn't strictly necessary, if you don't mind
> that the 'null sum' will produce zero.

It produces the wrong result, though:

>>> sum([3,4], base=12)
7

If I'm starting with 12 and summing 3 and 4, I expect to get 19.

Ideally the second argument should be ignored only if it isn't passed
in at all, and I don't know off-hand why the built-in sum doesn't do
this.  We really don't need to replace it, though.  If you want a
different sum behavior, just write your own.

def sum(iterable, *args):
    return reduce(operator.add, iterable, *args)

>>> sum([3,4])
7
>>> sum([3,4], 12)
19
>>> sum(['hello', 'world'])
'helloworld'

Cheers,
Ian

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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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