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Re: Python handles globals badly.

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On Sat, Sep 12, 2015 at 1:27 AM, Ian Kelly <ian.g.kelly@gmail.com> wrote:
> The exec still happily runs; it's just using its own private locals namespace.
>
> Tangent: does the help for exec need to be updated? It currently reads:
>
>     The globals and locals are dictionaries, defaulting to the current
>     globals and locals.  If only globals is given, locals defaults to it.
>
> Which would seem to indicate that if called from within a function
> with no globals or locals, the locals from the function would be used.

And that's the thing... I think. It's using locals(), which starts out
as a copy of the function's locals (in this example, empty), but
without assignment affecting anything. Which is more than a little
weird:

>>> def f():
...     x = [1]
...     exec("print(x); x[0] = 2; print(x); x = [3]; print(x)")
...     print(x)
...
>>> f()
[1]
[2]
[3]
[2]

It's kinda like how globals can shadow builtins, I think. Maybe.
Except that you can't del the name inside exec to unshadow and go back
to the outer version of it.

ChrisA

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Re: Python handles globals badly. tdev@freenet.de - 2015-09-10 15:25 -0700
  Re: Python handles globals badly. Emile van Sebille <emile@fenx.com> - 2015-09-10 15:40 -0700
  Re: Python handles globals badly. Ian Kelly <ian.g.kelly@gmail.com> - 2015-09-10 18:35 -0600
    Re: Python handles globals badly. Marko Rauhamaa <marko@pacujo.net> - 2015-09-11 07:34 +0300
      Re: Python handles globals badly. Chris Angelico <rosuav@gmail.com> - 2015-09-11 14:59 +1000
        Re: Python handles globals badly. Marko Rauhamaa <marko@pacujo.net> - 2015-09-11 08:15 +0300
          Re: Python handles globals badly. Chris Angelico <rosuav@gmail.com> - 2015-09-11 15:25 +1000
          Re: Python handles globals badly. Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-09-12 03:43 +0100
      Re: Python handles globals badly. Ian Kelly <ian.g.kelly@gmail.com> - 2015-09-10 23:07 -0600
        Re: Python handles globals badly. Marko Rauhamaa <marko@pacujo.net> - 2015-09-11 08:27 +0300
      Re: Python handles globals badly. Rustom Mody <rustompmody@gmail.com> - 2015-09-11 00:39 -0700
    Re: Python handles globals badly. Steven D'Aprano <steve@pearwood.info> - 2015-09-11 18:42 +1000
      Re: Python handles globals badly. Chris Angelico <rosuav@gmail.com> - 2015-09-11 19:16 +1000
      Re: Python handles globals badly. Ian Kelly <ian.g.kelly@gmail.com> - 2015-09-11 09:03 -0600
        Re: Python handles globals badly. Steven D'Aprano <steve@pearwood.info> - 2015-09-12 17:00 +1000
      Re: Python handles globals badly. Chris Angelico <rosuav@gmail.com> - 2015-09-12 01:15 +1000
      Re: Python handles globals badly. Ian Kelly <ian.g.kelly@gmail.com> - 2015-09-11 09:27 -0600
      Re: Python handles globals badly. Chris Angelico <rosuav@gmail.com> - 2015-09-12 01:44 +1000
      Re: Python handles globals badly. Ian Kelly <ian.g.kelly@gmail.com> - 2015-09-11 09:49 -0600
      Re: Python handles globals badly. Chris Angelico <rosuav@gmail.com> - 2015-09-12 01:55 +1000
      Re: Python handles globals badly. random832@fastmail.us - 2015-09-11 11:57 -0400
        Re: Python handles globals badly. Rustom Mody <rustompmody@gmail.com> - 2015-09-11 09:08 -0700
      Re: Python handles globals badly. Chris Angelico <rosuav@gmail.com> - 2015-09-12 02:04 +1000
      Re: Python handles globals badly. Ian Kelly <ian.g.kelly@gmail.com> - 2015-09-11 10:27 -0600
      Re: Python handles globals badly. Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-09-12 03:51 +0100
  Re: Python handles globals badly. MRAB <python@mrabarnett.plus.com> - 2015-09-11 02:17 +0100
  Re: Python handles globals badly. Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-09-12 03:27 +0100

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