[Python-Dev] Smoothing the transition from Python 2 to 3

Brett Cannon brett at python.org
Fri Jun 10 12:30:26 EDT 2016

On Thu, 9 Jun 2016 at 19:53 Mark Lawrence via Python-Dev <
python-dev at python.org> wrote:

> On 10/06/2016 00:43, Brett Cannon wrote:
> >
> > That's not what I'm saying at all (nor what I think Nick is saying);
> > more tooling to ease the transition is always welcomed. The point we are
> > trying to make is 2to3 is not considered best practice anymore, and so
> > targeting its specific output might not be the best use of your time.
> > I'm totally happy to have your fork work out and help give warnings for
> > situations where runtime semantics are the only way to know there will
> > be a problem that static analyzing tools can't handle and have the
> > porting HOWTO updated so that people can run their test suite with your
> > interpreter to help with that final bit of porting. I personally just
> > don't want to see you waste time on warnings that are handled by the
> > tools already or ignore the fact that six, modernize, and futurize can
> > help more than 2to3 typically can with the easy stuff when trying to
> > keep 2/3 compatibility. IOW some of us have become allergic to the word
> > "2to3" in regards to porting. :) But if you want to target 2to3 output
> > then by all means please do and your work will still be appreciated.
> >
> Given the above and that 2to3 appears to be unsupported* is there a case
> for deprecating it?

I don't think so because it's still a useful transpiler tool. Basically the
community has decided the standard rewriters included with 2to3 aren't how
people prefer to port, but 2to3 as a tool is the basis of both modernize
and futurize (as are some of those rewriters, but tweaked to do something

> *  There are 46 outstanding issues on the bug tracker.  Is the above the
> reason for this, I don't know?

Typically the bugs are for the rewrite rules and they are for edge cases
that no one wants to try and tackle as they are tough to cover (although
this is based on what comes through my inbox so my generalization could be


> --
> 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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