[Python-3000] PEP 3002 (Procedure for Backwards-Incompatible Changes)

[Brett Cannon]

On 4/29/06, Steven Bethard <steven.bethard at gmail.com> wrote:
> On 4/27/06, Guido van Rossum <guido at python.org> wrote:
> > I just read PEP 3002 and while I like most of what I see (thanks
> > Steven Bethard!) there's one section that stands out as problematic.
> [snip]
> > Rather than a version of Python
> > 3000, I suggest to add such warning code to Python 2.x, and not as a
> > branch, but as a permanent feature (that is however only enabled by a
> > command-line flag).
>
> Yes, I think it definitely makes more sense to make the modifications
> on 2.x.  I was hesitant to require integrating it into the main-line
> Python 2.x code because I was worried about affecting performance.
> But of course with a command-line flag, that point is moot.  So
> basically python3warn.py could be become "python -SOME_OPTION" where
> SOME_OPTION would enable all the Python 3.0 checks.
>
> So I guess the question then is what the option should enable.  Should
> it try to implement the Python 3.0 behavior?  Or should it just warn
> when the behavior is changed?  The former requires much more Python
> 3.0 code to be back-ported to Python 2.X, but would presumably give
> much better error reporting.  I'd love to require that, but I'm afraid
> of the work it would take.
>

My vote is the latter (i.e., just warnings).  Changes whose semantics
are desirable for 2.x will be backported.  Those that are not won't
be.  Thus we shouldn't go through the trouble of implementing the
semantics if for some reason it was not desirable to have them used by
default in the first place.

-Brett

> Steve
>
> P.S. I have commit access to the PEPs now, so I can update PEP 3002
> with whatever we decide.
> --
> Grammar am for people who can't think for myself.
>         --- Bucky Katt, Get Fuzzy
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