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Re: the global keyword:

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On Fri, Jun 24, 2016 at 1:00 AM, Steven D'Aprano <steve@pearwood.info> wrote:
> To be precise, for the builtins module specifically, you can *read* the
> value of the variable using just x, but you cannot *assign* to it unless
> you use the fully-qualified name builtins.x.

FWIW, you can execute code in any dict:

    >>> import builtins
    >>> exec(r'''
    ... foo = 'bar'
    ... ''', vars(builtins))
    >>> builtins.foo
    'bar'

The frame for an unoptimized CPython code object (used for modules and
the class statement) uses f_builtins, f_globals, and f_locals dicts
(or possibly a mapping in the case of f_locals) respectively for its
builtin, global, and local scopes. The frame for an optimized code
object uses a fast locals array instead of f_locals, in which case the
locals() function stores a snapshot of the locals to the f_locals
dict. A frame may also have a freevars array, which has cell objects
for closures (i.e. the nonlocal scope). For optimized code (i.e. a
function, but not a class body), locals() also includes a snapshot of
nonlocals, even though this doesn't make literal sense.

The above example executes code with all 3 scopes set to the same
dict. For example:

    >>> exec(r'''
    ... import sys
    ... f = sys._getframe()
    ... print(f.f_builtins is f.f_globals is f.f_locals)
    ... ''', vars(builtins))
    True

The CPython VM doesn't have an operation to store to the builtin
scope, since the language doesn't have a statement such as "builtin"
to declare a variable in this scope. The builtin scope is used as a
fallback for operations such as LOAD_NAME and LOAD_GLOBAL -- for
loading constants such as built-in functions, exceptions, __debug__,
and also the "_" attribute that gets updated by sys.displayhook.

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the global keyword: Marcin Rak <mrak@sightlineinnovation.com> - 2016-06-11 16:44 -0700
  Re: the global keyword: Random832 <random832@fastmail.com> - 2016-06-11 19:50 -0400
    Re: the global keyword: Marcin Rak <mrak@sightlineinnovation.com> - 2016-06-11 17:12 -0700
      Re: the global keyword: Random832 <random832@fastmail.com> - 2016-06-11 21:27 -0400
    Re: the global keyword: Lawrence D’Oliveiro <lawrencedo99@gmail.com> - 2016-06-11 20:15 -0700
      Re: the global keyword: Random832 <random832@fastmail.com> - 2016-06-12 14:46 -0400
  Re: the global keyword: MRAB <python@mrabarnett.plus.com> - 2016-06-12 01:09 +0100
    Re: the global keyword: Marcin Rak <mrak@sightlineinnovation.com> - 2016-06-11 17:13 -0700
      Re: the global keyword: Ned Batchelder <ned@nedbatchelder.com> - 2016-06-11 20:41 -0700
  Re: the global keyword: Random832 <random832@fastmail.com> - 2016-06-11 21:26 -0400
    Re: the global keyword: Steven D'Aprano <steve@pearwood.info> - 2016-06-12 13:38 +1000
      Re: the global keyword: Ned Batchelder <ned@nedbatchelder.com> - 2016-06-11 20:48 -0700
        Re: the global keyword: Marcin Rak <mrak@sightlineinnovation.com> - 2016-06-12 11:31 -0700
  Re: the global keyword: BartC <bc@freeuk.com> - 2016-06-12 20:07 +0100
    Re: the global keyword: Ned Batchelder <ned@nedbatchelder.com> - 2016-06-12 12:25 -0700
      Re: the global keyword: BartC <bc@freeuk.com> - 2016-06-12 22:10 +0100
        Re: the global keyword: Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2016-06-19 16:35 +0200
          Re: the global keyword: BartC <bc@freeuk.com> - 2016-06-19 22:20 +0100
            Re: the global keyword: Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2016-06-20 13:14 +0200
              Re: the global keyword: Steven D'Aprano <steve@pearwood.info> - 2016-06-20 22:15 +1000
                Re: the global keyword: Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2016-06-20 15:04 +0200
                Re: the global keyword: Random832 <random832@fastmail.com> - 2016-06-20 09:29 -0400
                Re: the global keyword: Steven D'Aprano <steve@pearwood.info> - 2016-06-21 00:53 +1000
                Re: the global keyword: Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2016-06-21 10:08 +0200
                Re: the global keyword: BartC <bc@freeuk.com> - 2016-06-21 11:41 +0100
                Re: the global keyword: Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2016-06-21 13:01 +0200
        Re: the global keyword: Joel Goldstick <joel.goldstick@gmail.com> - 2016-06-19 13:16 -0400
          Re: the global keyword: Lawrence D’Oliveiro <lawrencedo99@gmail.com> - 2016-06-19 22:50 -0700
          Re: the global keyword: BartC <bc@freeuk.com> - 2016-06-20 11:21 +0100
            Re: the global keyword: Steven D'Aprano <steve@pearwood.info> - 2016-06-20 22:03 +1000
    Re: the global keyword: Rick Johnson <rantingrickjohnson@gmail.com> - 2016-06-21 10:04 -0700
      Re: the global keyword: Random832 <random832@fastmail.com> - 2016-06-21 13:15 -0400
        Re: the global keyword: Rick Johnson <rantingrickjohnson@gmail.com> - 2016-06-21 15:20 -0700
          Re: the global keyword: Chris Angelico <rosuav@gmail.com> - 2016-06-22 08:32 +1000
            Re: the global keyword: Rick Johnson <rantingrickjohnson@gmail.com> - 2016-06-21 16:43 -0700
          Re: the global keyword: BartC <bc@freeuk.com> - 2016-06-22 00:15 +0100
            Re: the global keyword: Rick Johnson <rantingrickjohnson@gmail.com> - 2016-06-21 17:24 -0700
              Re: the global keyword: BartC <bc@freeuk.com> - 2016-06-22 10:24 +0100
                Re: the global keyword: Steven D'Aprano <steve@pearwood.info> - 2016-06-24 11:00 +1000
                Re: the global keyword: Chris Angelico <rosuav@gmail.com> - 2016-06-24 11:19 +1000
                Re: the global keyword: eryk sun <eryksun@gmail.com> - 2016-06-24 02:19 +0000
          Re: the global keyword: Rick Johnson <rantingrickjohnson@gmail.com> - 2016-06-21 16:50 -0700

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