Re: sum works in sequences (Python 3)

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From	Neil Cerutti <neilc@norwich.edu>
Newsgroups	comp.lang.python
Subject	Re: sum works in sequences (Python 3)
Date	19 Sep 2012 15:06:43 GMT
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On 2012-09-19, Ian Kelly <ian.g.kelly@gmail.com> wrote:
> It notes in the doc string that it does not work on strings:
>
> sum(...)
>     sum(sequence[, start]) -> value
>
>     Returns the sum of a sequence of numbers (NOT strings) plus
>     the value of parameter 'start' (which defaults to 0).  When
>     the sequence is empty, returns start.
>
> I think this restriction is mainly for efficiency.  sum(['a',
> 'b', 'c', 'd', 'e']) would be the equivalent of 'a' + 'b' + 'c'
> + 'd' + 'e', which is an inefficient way to add together
> strings.  You should use ''.join instead:

While the docstring is still useful, it has diverged from the
documentation a little bit.

  sum(iterable[, start]) 

  Sums start and the items of an iterable from left to right and
  returns the total. start defaults to 0. The iterable‘s items
  are normally numbers, and the start value is not allowed to be
  a string.

  For some use cases, there are good alternatives to sum(). The
  preferred, fast way to concatenate a sequence of strings is by
  calling ''.join(sequence). To add floating point values with
  extended precision, see math.fsum(). To concatenate a series of
  iterables, consider using itertools.chain().

Are iterables and sequences different enough to warrant posting a
bug report?

-- 
Neil Cerutti

Thread

sum works in sequences (Python 3) Franck Ditter <franck@ditter.org> - 2012-09-19 16:41 +0200
  Re: sum works in sequences (Python 3) Joel Goldstick <joel.goldstick@gmail.com> - 2012-09-19 10:57 -0400
  Re: sum works in sequences (Python 3) Neil Cerutti <neilc@norwich.edu> - 2012-09-19 14:57 +0000
  Re: sum works in sequences (Python 3) Ian Kelly <ian.g.kelly@gmail.com> - 2012-09-19 09:03 -0600
    Re: sum works in sequences (Python 3) Neil Cerutti <neilc@norwich.edu> - 2012-09-19 15:06 +0000
      Re: sum works in sequences (Python 3) Ian Kelly <ian.g.kelly@gmail.com> - 2012-09-19 09:24 -0600
      Re: sum works in sequences (Python 3) Steve Howell <showell30@yahoo.com> - 2012-09-19 08:37 -0700
        Re: sum works in sequences (Python 3) Ian Kelly <ian.g.kelly@gmail.com> - 2012-09-19 12:33 -0600
          Re: sum works in sequences (Python 3) Steve Howell <showell30@yahoo.com> - 2012-09-19 11:43 -0700
    Re: sum works in sequences (Python 3) Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-09-19 16:14 +0000
  Re: sum works in sequences (Python 3) Alister <alister.ware@ntlworld.com> - 2012-09-19 15:07 +0000
    Re: sum works in sequences (Python 3) Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-09-19 16:18 +0000
    Re: sum works in sequences (Python 3) Terry Reedy <tjreedy@udel.edu> - 2012-09-19 14:49 -0400
    Re: sum works in sequences (Python 3) Hans Mulder <hansmu@xs4all.nl> - 2012-09-20 00:25 +0200

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