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Re: Default Value

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Date Thu, 20 Jun 2013 21:02:07 -0500
From Tim Chase <python.list@tim.thechases.com>
To Roy Smith <roy@panix.com>
Subject Re: Default Value
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On 2013-06-20 21:40, Roy Smith wrote:
> In article <mailman.3647.1371777895.3114.python-list@python.org>,
>  Tim Chase <python.list@tim.thechases.com> wrote:
> 
> > On 2013-06-21 01:08, Steven D'Aprano wrote:
> > > Here's my syntax plucked out of thin air:
> > > 
> > > def func(arg, x=expression, !y=expression):
> > >     ...
> > > 
> > > where y=expression is late-bound, and the above is compiled to:
> > > 
> > > def func(arg, x=expression, y=None):
> > >     if y is None:
> > >         y = expression
> > >     ...
> > 
> > I think it would have to translate to something like
> > 
> >   _temp_semaphore = object()
> >   def func(arg, x=expression, y=_temp_semaphore):
> >     if y is _temp_semaphore:
> >       y = expression
> > 
> >     ...
> 
> You can go around and around on that one.  Whatever distinguished
> value you set aside to mean "no argument passed", somebody will
> come up with a use case for why they might want to pass that as a
> real value.

That's why I suggested using an "is" test against a custom/local(ish)
semaphore instance that is only used for the particular invocation in
which the "def" statement occurs.

-tkc

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Default Value Ahmed Abdulshafy <abdulshafy@gmail.com> - 2013-06-19 12:17 -0700
  Re: Default Value Jussi Piitulainen <jpiitula@ling.helsinki.fi> - 2013-06-19 22:35 +0300
  Re: Default Value Rick Johnson <rantingrickjohnson@gmail.com> - 2013-06-19 12:38 -0700
    Re: Default Value rusi <rustompmody@gmail.com> - 2013-06-20 05:57 -0700
      Re: Default Value Roy Smith <roy@panix.com> - 2013-06-20 09:19 -0400
        Re: Default Value rusi <rustompmody@gmail.com> - 2013-06-20 06:31 -0700
        Re: Default Value Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-06-21 00:17 +0000
          Re: Default Value Roy Smith <roy@panix.com> - 2013-06-20 20:25 -0400
      Re: Default Value Rick Johnson <rantingrickjohnson@gmail.com> - 2013-06-20 07:49 -0700
        Re: Default Value Chris Angelico <rosuav@gmail.com> - 2013-06-21 01:38 +1000
          Re: Default Value Rick Johnson <rantingrickjohnson@gmail.com> - 2013-06-20 11:05 -0700
            Re: Default Value Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-06-21 00:57 +0000
              Re: Default Value Rick Johnson <rantingrickjohnson@gmail.com> - 2013-06-20 20:16 -0700
                Re: Default Value Chris Angelico <rosuav@gmail.com> - 2013-06-21 17:10 +1000
                Re: Default Value Rick Johnson <rantingrickjohnson@gmail.com> - 2013-06-21 07:32 -0700
                Re: Default Value Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-06-21 16:22 +0000
            Re: Default Value Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-06-21 15:57 +0000
              Re: Default Value Rick Johnson <rantingrickjohnson@gmail.com> - 2013-06-21 10:01 -0700
                Re: Default Value Rotwang <sg552@hotmail.co.uk> - 2013-06-21 18:47 +0100
                Re: Default Value Rick Johnson <rantingrickjohnson@gmail.com> - 2013-06-21 11:26 -0700
                Re: Default Value Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-06-21 18:37 +0000
                Re: Default Value Rick Johnson <rantingrickjohnson@gmail.com> - 2013-06-21 12:18 -0700
                Re: Default Value Rick Johnson <rantingrickjohnson@gmail.com> - 2013-06-21 12:35 -0700
                Re: Default Value Chris Angelico <rosuav@gmail.com> - 2013-06-22 05:07 +1000
                Re: Default Value Neil Cerutti <neilc@norwich.edu> - 2013-06-21 19:20 +0000
                Re: Default Value Rick Johnson <rantingrickjohnson@gmail.com> - 2013-06-21 13:27 -0700
                Re: Default Value Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-06-22 01:31 +0000
                Re: Default Value Chris Angelico <rosuav@gmail.com> - 2013-06-22 11:40 +1000
                Re: Default Value Rick Johnson <rantingrickjohnson@gmail.com> - 2013-06-21 18:42 -0700
                Re: Default Value MRAB <python@mrabarnett.plus.com> - 2013-06-22 03:04 +0100
                Re: Default Value Rick Johnson <rantingrickjohnson@gmail.com> - 2013-06-21 19:32 -0700
                Re: Default Value MRAB <python@mrabarnett.plus.com> - 2013-06-22 20:36 +0100
                Re: Default Value Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2013-06-22 18:51 -0400
                Re: Default Value rusi <rustompmody@gmail.com> - 2013-06-21 19:43 -0700
                Re: Default Value Mark Lawrence <breamoreboy@yahoo.co.uk> - 2013-06-22 09:26 +0100
                Re: Default Value MRAB <python@mrabarnett.plus.com> - 2013-06-21 20:25 +0100
                Re: Default Value Rick Johnson <rantingrickjohnson@gmail.com> - 2013-06-21 13:44 -0700
                Re: Default Value MRAB <python@mrabarnett.plus.com> - 2013-06-21 23:49 +0100
                Re: Default Value Rick Johnson <rantingrickjohnson@gmail.com> - 2013-06-21 16:51 -0700
                Re: Default Value MRAB <python@mrabarnett.plus.com> - 2013-06-22 02:54 +0100
                Re: Default Value Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-06-22 01:15 +0000
                Re: Default Value Ian Kelly <ian.g.kelly@gmail.com> - 2013-06-21 19:27 -0600
                Re: Default Value rusi <rustompmody@gmail.com> - 2013-06-21 19:32 -0700
                Re: Default Value Rick Johnson <rantingrickjohnson@gmail.com> - 2013-06-21 19:55 -0700
                Re: Default Value rusi <rustompmody@gmail.com> - 2013-06-21 23:23 -0700
                Re: Default Value Rick Johnson <rantingrickjohnson@gmail.com> - 2013-06-22 08:07 -0700
                Re: Default Value rusi <rustompmody@gmail.com> - 2013-06-22 08:31 -0700
                Re: Default Value rusi <rustompmody@gmail.com> - 2013-06-22 09:11 -0700
                Re: Default Value Grant Edwards <invalid@invalid.invalid> - 2013-06-24 14:22 +0000
                Re: [SPAM] Re: Default Value MRAB <python@mrabarnett.plus.com> - 2013-06-24 16:22 +0100
                Re: Default Value Chris Angelico <rosuav@gmail.com> - 2013-06-22 11:41 +1000
                Re: Default Value Michael Torrie <torriem@gmail.com> - 2013-06-21 20:46 -0600
                Re: Default Value Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2013-06-22 16:40 +0200
                Re: Default Value Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2013-06-22 12:49 -0400
                Re: Default Value Ian Kelly <ian.g.kelly@gmail.com> - 2013-06-22 12:57 -0600
                Re: Default Value Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2013-06-22 18:48 -0400
                Re: Default Value Rotwang <sg552@hotmail.co.uk> - 2013-06-22 00:40 +0100
                Re: Default Value Rick Johnson <rantingrickjohnson@gmail.com> - 2013-06-21 18:15 -0700
                Re: Default Value Chris Angelico <rosuav@gmail.com> - 2013-06-22 11:37 +1000
                Re: Default Value Ian Kelly <ian.g.kelly@gmail.com> - 2013-06-21 19:42 -0600
                Re: Default Value Ian Kelly <ian.g.kelly@gmail.com> - 2013-06-21 19:38 -0600
                Re: Default Value Rick Johnson <rantingrickjohnson@gmail.com> - 2013-06-21 19:40 -0700
                Re: Default Value Rotwang <sg552@hotmail.co.uk> - 2013-06-22 03:01 +0100
                Re: Default Value Chris Angelico <rosuav@gmail.com> - 2013-06-22 12:18 +1000
                Re: Default Value Rotwang <sg552@hotmail.co.uk> - 2013-06-22 03:25 +0100
                Re: Default Value Rotwang <sg552@hotmail.co.uk> - 2013-06-22 18:19 +0100
                Re: Default Value Rick Johnson <rantingrickjohnson@gmail.com> - 2013-06-22 11:49 -0700
                Re: Default Value Rotwang <sg552@hotmail.co.uk> - 2013-06-23 01:49 +0100
        Re: Default Value rusi <rustompmody@gmail.com> - 2013-06-20 10:12 -0700
          Re: Default Value Chris Angelico <rosuav@gmail.com> - 2013-06-21 03:19 +1000
            Re: Default Value rusi <rustompmody@gmail.com> - 2013-06-20 10:30 -0700
          Re: Default Value Ian Kelly <ian.g.kelly@gmail.com> - 2013-06-20 11:57 -0600
            Re: Default Value rusi <rustompmody@gmail.com> - 2013-06-20 11:15 -0700
            Re: Default Value Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-06-21 01:08 +0000
              Re: Default Value Tim Chase <python.list@tim.thechases.com> - 2013-06-20 20:26 -0500
                Re: Default Value Roy Smith <roy@panix.com> - 2013-06-20 21:40 -0400
                Re: Default Value Tim Chase <python.list@tim.thechases.com> - 2013-06-20 21:02 -0500
          Re: Default Value Rick Johnson <rantingrickjohnson@gmail.com> - 2013-06-20 11:07 -0700
            Re: Default Value alex23 <wuwei23@gmail.com> - 2013-06-21 10:55 +1000
          Re: Default Value 88888 Dihedral <dihedral88888@gmail.com> - 2013-06-20 19:18 -0700
          Re: Default Value Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-06-21 02:26 +0000
          Re: Default Value "Lefavor, Matthew (GSFC-582.0)[MICROTEL LLC]" <matthew.lefavor@nasa.gov> - 2013-06-20 17:28 -0500
            Re: Default Value Rick Johnson <rantingrickjohnson@gmail.com> - 2013-06-21 08:17 -0700
        Re: Default Value Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-06-21 01:28 +0000
  Re: Default Value Gary Herron <gherron@digipen.edu> - 2013-06-19 12:57 -0700
  Re: Default Value Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-06-20 01:17 +0000

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