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Re: Values and objects

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Date Sat, 10 May 2014 12:10:21 -0700
From Ethan Furman <ethan@stoneleaf.us>
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Subject Re: Values and objects
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On 05/10/2014 02:32 AM, Chris Angelico wrote:
>
> Tell me, what may this function do in a compliant Python?
>
> def demo():
>      ret = spam
>      spam = 23
>      return ret
>
> In CPython, that'll raise UnboundLocalError, because the local
> variable 'spam' does already exist, and currently has no value (no
> object bound to it).

No, it does not exist -- or, more accurately, it does not exist *yet* but will.  The fact that there is a slot waiting 
for what will be spam is a cpython implementation detail.

And if you don't like that argument (although it is a perfectly sound and correct argument), think of the module name space:

ret = spam
spam = 23

will net you a simple NameError, because spam has not yet been created.


>  If a compliant Python implementation is allowed
> to have this return the value of a global or builtin spam, then I
> would agree that you can create variables at run time.

See module example above.  This behavior is not allowed in functions for scope and sanity (mostly sanity) reasons.

--
~Ethan~

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Thread

Re: Pass variable by reference Ned Batchelder <ned@nedbatchelder.com> - 2014-05-06 16:31 -0400
  Re: Pass variable by reference Mark H Harris <harrismh777@gmail.com> - 2014-05-06 16:00 -0500
    Re: Pass variable by reference Ned Batchelder <ned@nedbatchelder.com> - 2014-05-06 17:27 -0400
    Re: Pass variable by reference Chris Angelico <rosuav@gmail.com> - 2014-05-07 09:46 +1000
      Re: Pass variable by reference Rustom Mody <rustompmody@gmail.com> - 2014-05-06 19:18 -0700
        Re: Pass variable by reference Chris Angelico <rosuav@gmail.com> - 2014-05-07 12:39 +1000
          Re: Pass variable by reference Rustom Mody <rustompmody@gmail.com> - 2014-05-06 19:54 -0700
            Re: Pass variable by reference Steven D'Aprano <steve@pearwood.info> - 2014-05-07 04:59 +0000
      Re: Pass variable by reference Mark H Harris <harrismh777@gmail.com> - 2014-05-07 13:11 -0500
        Re: Pass variable by reference Marko Rauhamaa <marko@pacujo.net> - 2014-05-08 00:22 +0300
          Values and objects [was Re: Pass variable by reference] Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-05-08 01:08 +0000
            Re: Values and objects [was Re: Pass variable by reference] Mark H Harris <harrismh777@gmail.com> - 2014-05-09 16:56 -0500
              Re: Values and objects Marko Rauhamaa <marko@pacujo.net> - 2014-05-10 01:34 +0300
                Re: Values and objects Ben Finney <ben@benfinney.id.au> - 2014-05-10 10:24 +1000
                Re: Values and objects Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-05-10 01:01 +0000
                Re: Values and objects Rustom Mody <rustompmody@gmail.com> - 2014-05-09 19:19 -0700
                Re: Values and objects Chris Angelico <rosuav@gmail.com> - 2014-05-10 12:33 +1000
                Re: Values and objects Rustom Mody <rustompmody@gmail.com> - 2014-05-09 20:05 -0700
                Re: Values and objects Mark H Harris <harrismh777@gmail.com> - 2014-05-09 23:15 -0500
                Re: Values and objects Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-05-10 06:15 +0000
                Re: Values and objects Chris Angelico <rosuav@gmail.com> - 2014-05-10 17:21 +1000
                Re: Values and objects Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-05-10 09:09 +0000
                Re: Values and objects Chris Angelico <rosuav@gmail.com> - 2014-05-10 19:32 +1000
                Re: Values and objects Ethan Furman <ethan@stoneleaf.us> - 2014-05-10 12:10 -0700
                Re: Values and objects MRAB <python@mrabarnett.plus.com> - 2014-05-10 20:22 +0100
                Re: Values and objects Ethan Furman <ethan@stoneleaf.us> - 2014-05-10 12:28 -0700
                Re: Values and objects Terry Reedy <tjreedy@udel.edu> - 2014-05-10 16:16 -0400
                Re: Values and objects Terry Reedy <tjreedy@udel.edu> - 2014-05-10 16:24 -0400
                Re: Values and objects Devin Jeanpierre <jeanpierreda@gmail.com> - 2014-05-10 14:03 -0700
                Re: Values and objects Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-05-11 03:17 +0000
                Re: Values and objects Chris Angelico <rosuav@gmail.com> - 2014-05-11 13:30 +1000
                Re: Values and objects Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-05-11 05:11 +0000
                Re: Values and objects Chris Angelico <rosuav@gmail.com> - 2014-05-11 15:22 +1000
                Re: Values and objects Rustom Mody <rustompmody@gmail.com> - 2014-05-10 22:31 -0700
                Re: Values and objects Marko Rauhamaa <marko@pacujo.net> - 2014-05-11 09:21 +0300
                Re: Values and objects Rustom Mody <rustompmody@gmail.com> - 2014-05-10 23:48 -0700
                Re: Values and objects Marko Rauhamaa <marko@pacujo.net> - 2014-05-11 18:10 +0300
                Re: Values and objects Jussi Piitulainen <jpiitula@ling.helsinki.fi> - 2014-05-11 11:26 +0300
                Re: Values and objects Rustom Mody <rustompmody@gmail.com> - 2014-05-11 01:48 -0700
                Re: Values and objects Jussi Piitulainen <jpiitula@ling.helsinki.fi> - 2014-05-11 15:22 +0300
                Re: Values and objects Marko Rauhamaa <marko@pacujo.net> - 2014-05-11 18:46 +0300
                Re: Values and objects Marko Rauhamaa <marko@pacujo.net> - 2014-05-11 22:56 +0300
                Re: Values and objects Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-05-11 12:51 +0000
                Re: Values and objects Rustom Mody <rustompmody@gmail.com> - 2014-05-11 07:12 -0700
                Re: Values and objects Ethan Furman <ethan@stoneleaf.us> - 2014-05-10 22:42 -0700
                Re: Values and objects Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-05-11 06:40 +0000
                Re: Values and objects Chris Angelico <rosuav@gmail.com> - 2014-05-11 09:18 +1000
                Re: Values and objects Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-05-11 03:11 +0000
                Re: Values and objects Rotwang <sg552@hotmail.co.uk> - 2014-05-11 14:46 +0100
                Re: Values and objects Ned Batchelder <ned@nedbatchelder.com> - 2014-05-11 14:40 -0400
                Re: Values and objects Rotwang <sg552@hotmail.co.uk> - 2014-05-12 00:06 +0100
                Re: Values and objects Ethan Furman <ethan@stoneleaf.us> - 2014-05-10 18:28 -0700
                Re: Values and objects Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-05-11 07:24 +0000
                Re: Values and objects Chris Angelico <rosuav@gmail.com> - 2014-05-11 11:59 +1000
                Re: Values and objects Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-05-11 07:29 +0000
                Re: Values and objects Ethan Furman <ethan@stoneleaf.us> - 2014-05-10 21:46 -0700
                Re: [Python-Dev] Values and objects Chris Angelico <rosuav@gmail.com> - 2014-05-11 16:08 +1000
                Re: Values and objects albert@spenarnc.xs4all.nl (Albert van der Horst) - 2014-05-17 14:26 +0000
                Re: Values and objects Chris Angelico <rosuav@gmail.com> - 2014-05-10 11:58 +1000
                Re: Values and objects Marko Rauhamaa <marko@pacujo.net> - 2014-05-10 10:57 +0300
                Re: Values and objects Jussi Piitulainen <jpiitula@ling.helsinki.fi> - 2014-05-10 11:06 +0300
                Re: Values and objects Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2014-05-10 12:07 -0400
        Re: Pass variable by reference Chris Angelico <rosuav@gmail.com> - 2014-05-08 11:31 +1000
          Re: Pass variable by reference Mark H Harris <harrismh777@gmail.com> - 2014-05-09 17:30 -0500
            Abstractions [was Re: Pass variable by reference] Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-05-10 00:58 +0000
              Re: Abstractions [was Re: Pass variable by reference] Mark H Harris <harrismh777@gmail.com> - 2014-05-09 21:17 -0500
  Re: Pass variable by reference Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-05-07 01:14 +0000

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