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Re: Question about name scope

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On Wed, Feb 1, 2012 at 3:53 PM, Ethan Furman <ethan@stoneleaf.us> wrote:
> --> def f(x, y):
>
> ...     locals()[x] = y
> ...     print(vars())
> ...     exec('print (' + x + ')')
> ...     print(x)
> ...
> --> f('a', 42)
>
> {'y': 42, 'x': 'a', 'a': 42}
> 42
> a
>
> Indeed -- the point to keep in mind is that locals() can become out of sync
> with the functions actual variables.  Definitely falls in the camp of "if
> you don't know *exactly* what you are doing, do not play this way!"

Sure, but that's not actually out of sync.  The argument of your exec
evaluates to 'print (a)'.  You get two different results because
you're actually printing two different variables.  You can get the
dict temporarily out of sync:

>>> def f(x, y):
...     frob = None
...     loc = locals()
...     loc[x] = y
...     print(loc)
...     print(locals())
...     print(loc)
...
>>> f('frob', 42)
{'y': 42, 'x': 'frob', 'frob': 42, 'loc': {...}}
{'y': 42, 'x': 'frob', 'frob': None, 'loc': {...}}
{'y': 42, 'x': 'frob', 'frob': None, 'loc': {...}}

In this case, 'frob' is updated to 42 in the dict, but the optimized
local is not updated.  Calling locals() again refreshes the dict.

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Question about name scope Olive <diolu@bigfoot.com> - 2012-02-01 18:11 +0100
  Re: Question about name scope Rick Johnson <rantingrickjohnson@gmail.com> - 2012-02-01 09:21 -0800
  Re: Question about name scope Ethan Furman <ethan@stoneleaf.us> - 2012-02-01 09:43 -0800
  Re: Question about name scope Dave Angel <d@davea.name> - 2012-02-01 12:36 -0500
    Re: Question about name scope Mel Wilson <mwilson@the-wire.com> - 2012-02-01 13:47 -0500
      Re: Question about name scope Ian Kelly <ian.g.kelly@gmail.com> - 2012-02-01 14:49 -0700
      Re: Question about name scope Ian Kelly <ian.g.kelly@gmail.com> - 2012-02-01 15:38 -0700
      Re: Question about name scope Ethan Furman <ethan@stoneleaf.us> - 2012-02-01 14:24 -0800
      Re: Question about name scope Ian Kelly <ian.g.kelly@gmail.com> - 2012-02-01 16:00 -0700
      Re: Question about name scope Ethan Furman <ethan@stoneleaf.us> - 2012-02-01 15:08 -0800
      Re: Question about name scope Ian Kelly <ian.g.kelly@gmail.com> - 2012-02-01 16:47 -0700
      Re: Question about name scope Ethan Furman <ethan@stoneleaf.us> - 2012-02-01 14:53 -0800
        Re: Question about name scope Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-02-02 00:34 +0000
      Re: Question about name scope Ethan Furman <ethan@stoneleaf.us> - 2012-02-01 15:59 -0800
      Re: Question about name scope Ethan Furman <ethan@stoneleaf.us> - 2012-02-01 15:41 -0800
      Re: Question about name scope Ethan Furman <ethan@stoneleaf.us> - 2012-02-01 15:51 -0800
  Re: Question about name scope Chris Rebert <clp2@rebertia.com> - 2012-02-01 09:38 -0800
  Re: Question about name scope Christian Heimes <lists@cheimes.de> - 2012-02-01 18:50 +0100

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