[Python-Dev] 2.7 Release? 2.7 == last of the 2.x line?

Mike Krell mbk.lists at gmail.com
Fri Nov 6 05:12:25 CET 2009

On Thu, Nov 5, 2009 at 1:08 PM, "Martin v. Löwis" <martin at v.loewis.de>wrote:

> > Mike Krell wrote:
> >>     Well, 3to2 would then be an option for you: use Python 3 as the
> source
> >>     language.
> >
> > Making life easier for 3to2 is an *excellent* rationale for backports.

Clarifying a bit of potentially misleading editing:  I wrote neither of the
statements quoted above.  M v L wrote the first and Nick C. wrote the

> I'm skeptical. If new features get added to 2.7: why would that simplify
> 3to2? It couldn't *use* these features, since it surely would have to
> support 2.6 and earlier as well.
> Not sure what 3to2 would do about difficult-to-convert 3.x feature (as,
> perhaps, the nonlocal keyword). If it currently gives up, it then may
> offer you to restrict your target versions to 2.7+. Not sure whether
> users would use that option, though - perhaps they rather stop using
> nonlocal in 3.x if 3to2 cannot support it for all 2.x versions they are
> interested in.

> Perhaps 3to2 has a work-around that still provides a good backport in
> most cases. Then, the backport would not make the tool any simpler: if
> 3to2 would start using the backport, it would actually get more
> complicated (not easier), as it now needs to support two cases.

I basically agree with you here, except perhaps for the likely definition of
"versions they are interested in".  You have suggested on several occasions
that a 2.7 (or 2.8) containing new syntax such as nonlocal would be of
limited value because the vast majority of developers interested in
supporting 2.x would have to support 2.6 as well.  I respectfully suggest
that may not necessarily be the case.  I suspect that there are lots of
small fish out there like me who have the luxury of being able to hop onto
whatever version of the language suits them the best.  Not to mention all of
the new users who will be drawn to Python over the next several years while
the 3.x standard library and third party library situation becomes more
stable and comprehensive.  Why not make the 2.x feature set the best it can
be given the likelihood that 2.x will be the most compelling alternative to
many users until the 3.x libraries mature?

Of course, it's easy for me to ask other people to the hard work.  It might
be fun to take a crack at implementing nonlocal myself, but I know next to
nothing about the implementation of CPython.  By the time I pestered y'all
with enough questions to get up to speed, you'd probably wish you'd just
implemented it yourself -- less work :-)

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