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Re: sum works in sequences (Python 3)

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On Wed, Sep 19, 2012 at 8:41 AM, Franck Ditter <franck@ditter.org> wrote:
> Hello,
> I wonder why sum does not work on the string sequence in Python 3 :
>
>>>> sum((8,5,9,3))
> 25
>>>> sum([5,8,3,9,2])
> 27
>>>> sum('rtarze')
> TypeError: unsupported operand type(s) for +: 'int' and 'str'
>
> I naively thought that sum('abc') would expand to 'a'+'b'+'c'
> And the error message is somewhat cryptic...

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:

>>> ''.join('abc')
'abc'

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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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