[Python-Dev] Re: Stability and change

Alex Martelli aleax@aleax.it
Mon, 8 Apr 2002 22:52:58 +0200

On Monday 08 April 2002 22:45, Skip Montanaro wrote:
>     Guido> I think version dependency management is subject to the
> Logajan Guido> paradox. :-(
> Can you state that succintly for us? :-)

"Python keeps being maintained yet it *never* happens that release
X (for any X and Y) can run some code that release Y cannot run".

It's unachievable (as well as unreasonable) and thus I don't think it 
should be considered.

A desire that I think more reasonable (still unachievable, but one can
come closer) is a similar wish stated only for Y > X.  In practice we
do need break-points where such backwards compatibility cannot
be guaranteed ("major releases") -- further, I think that for the wish
to be both achievable AND compatible with other important goals it
must be nuanced ('some code' becoming 'CORRECT code', for
example -- broken code that HAPPENS to run by accident is quite
another thing: although for some users the difference can be hard
to appreciate, the concept of 'undefined behavior' is, I believe, known
widely enough to rely on it a bit, at least where the docs mention it).