[Python-Dev] Is it intentional that "sys.__debug__ = 1" is illegal in Python 2.7?

[Steven D'Aprano]

On Sat, 31 Jul 2010 07:44:42 am Guido van Rossum wrote:
> On Fri, Jul 30, 2010 at 1:53 PM, Barry Warsaw <barry at python.org> 
wrote:
> > On Jul 30, 2010, at 01:42 PM, Guido van Rossum wrote:
> >>Well it is a reserved name so those packages that were setting it
> >>should have known that they were using undefined behavior that
> >> could change at any time.
> >
> > Shouldn't it be described here then?
> >
> > http://docs.python.org/reference/lexical_analysis.html#identifiers
>
> No, since it is covered here:
>
> http://docs.python.org/reference/lexical_analysis.html#reserved-class
>es-of-identifiers


I have a small concern about the wording of that, specifically this:

"System-defined names. These names are defined by the interpreter and 
its implementation (including the standard library); applications 
SHOULD NOT EXPECT TO DEFINE additional names using this convention. The 
set of names of this class defined by Python may be extended in future 
versions."  [emphasis added]

This implies to me that at some time in the future, Python may make it 
illegal to assign to any __*__ name apart from those in a list 
of "approved" methods. Is that the intention? I have always understood 
that if you create your own __*__ names, you risk clashing with a 
special method, but otherwise it is allowed, if disapproved off. I 
would not like to see it become forbidden.


-- 
Steven D'Aprano