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Re: Clearing globals in CPython

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On 01/10/2014 17:00, Steven D'Aprano wrote:
> Out of curiosity, I ran:
>
> globals().clear()
>
> in the interactive interpreter. It broke much more than I expected!
> Built-ins were no longer available, and import stopped working.
>
> I expected that global variables would be all lost, but built-ins would
> remain, since they don't live in the global namespace. I was wrong:
>
>>>> globals().clear()
>>>> x = len([])
> Traceback (most recent call last):
>    File "<stdin>", line 1, in <module>
> NameError: name 'len' is not defined
>
> The reason, I think, is that CPython has a special __builtins__ global
> variable that the interpreter uses to access built-in functions. What
> *appears* to be happening is that if that __builtins__ global is missing,
> CPython can not access the built-ins.
>
> (Supporting this interpretation: IronPython, like CPython, has a
> __builtins__ global, and behaves the same when the globals() are cleared.
> Jython, which does not have a __builtins__ global, does not.)
>
> Well that's okay, I thought to myself, I'll just import the built-in
> functions:
>
>>>> from builtins import len  # use '__builtin__' in Python 2
> Traceback (most recent call last):
>    File "<stdin>", line 1, in <module>
> ImportError: __import__ not found
>
> Oops.
>
> So, with no built-ins available, import no longer works. That makes things
> rather tricky.
>
> Obviously the easiest way to recover is to exit the current session and
> restart it, but as a challenge, can we recover from this state?
>
>

We obviously need a Restart Command.

-- 
My fellow Pythonistas, ask not what our language can do for you, ask
what you can do for our language.

Mark Lawrence

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Clearing globals in CPython Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-10-02 02:00 +1000
  Re: Clearing globals in CPython Chris Angelico <rosuav@gmail.com> - 2014-10-02 02:14 +1000
  Re: Clearing globals in CPython Chris Kaynor <ckaynor@zindagigames.com> - 2014-10-01 10:08 -0700
  Re: Clearing globals in CPython Peter Otten <__peter__@web.de> - 2014-10-01 19:24 +0200
    Re: Clearing globals in CPython Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-10-02 18:11 +1000
      Re: Clearing globals in CPython Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-10-02 09:30 +0100
    Re: Clearing globals in CPython jakubo <jakubo@example.org> - 2014-10-06 09:05 +0000
      Re: Clearing globals in CPython Steven D'Aprano <steve@pearwood.info> - 2014-10-06 09:08 +0000
        Re: Clearing globals in CPython Chris Angelico <rosuav@gmail.com> - 2014-10-06 20:30 +1100
  Re: Clearing globals in CPython Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-10-01 19:17 +0100
  Re: Clearing globals in CPython Terry Reedy <tjreedy@udel.edu> - 2014-10-01 14:44 -0400
  Re: Clearing globals in CPython Marco Buttu <marco.buttu@gmail.com> - 2014-10-01 18:39 +0200
  Re: Clearing globals in CPython Grant Edwards <invalid@invalid.invalid> - 2014-10-02 14:07 +0000
    Re: Clearing globals in CPython Chris Angelico <rosuav@gmail.com> - 2014-10-03 00:12 +1000
    Re: Clearing globals in CPython Stefan Behnel <stefan_ml@behnel.de> - 2014-10-03 07:26 +0200

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