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

[Neil Schemenauer]

On 6/10/2016 10:49 AM, Nick Coghlan wrote:
> What Brett said is mostly accurate for me, except with one slight
> caveat: I've been explicitly trying to nudge you towards making the
> *existing tools better*, rather than introducing new tools. With
> modernize and futurize we have a fairly clear trade-off ("Do you want
> your code to look more like Python 2 or more like Python 3?"), and
> things like "pylint --py3k" and the static analyzers are purely
> additive to the migration process (so folks can take them or leave
> them), but alternate interpreter builds and new converters have really
> high barriers to adoption.

I agree with that idea.  If there is anything that is "clean" enough, it 
should be merged with either 2.7.x or 3.x.  There is nothing in my tree 
that can be usefully merged though.

> More -3 warnings in Python 2.7 are definitely welcome (since those can
> pick up runtime behaviors that the static analysers miss), and if
> there are things the existing code converters and static analysers
> *could* detect but don't, that's a fruitful avenue for improvement as
> well.
We are really limited on what can be done with the bytes/string issue 
because in Python 2 there is no distinct type for bytes. Also, the 
standard library does all sorts of unclean mixing of str and unicode so 
a warning would spew a lot of noise.

Likewise, a warning about comparison behavior (None, default ordering of 
types) would also not be useful because there is so much standard 
library code that would spew warnings.