[Python-ideas] PEP 511: API for code transformers

[Brett Cannon]

On Fri, Jan 29, 2016, 11:57 Andrew Barnert via Python-ideas <
python-ideas at python.org> wrote:

> On Jan 29, 2016, at 06:10, Nick Coghlan <ncoghlan at gmail.com> wrote:
> >
> > PEP 511 erases that piece of incidental complexity and say, "If you
> > want to apply a genuinely global transformation, this is how you do
> > it". The fact we already have decorators and import hooks is why I
> > think PEP 511 can safely ignore the use cases that those handle.
>
> I think this is the conclusion I was hoping to reach, but wasn't sure how
> to get there. I'm happy with PEP 511 not trying to serve cases like MacroPy
> and Hy and the example from the byteplay docs, especially so if ignoring
> them makes PEP 511 simpler, as long as it can explain why it's ignoring
> them. And a shorter version of your argument should serve as such an
> explanation.
>
> But the other half of my point was that too many people (even very
> experienced developers like most of the people on this list) think there's
> more incidental complexity than there is, and that's also a problem. For
> example, "I want to write a global processor for local experimentation
> purposes so I can play with my idea before posting it to Python-ideas" is
> not a bad desire. And, if people think it's way too hard to do with a
> quick&dirty import hook, they're naturally going to ask why PEP 511 doesn't
> help them out by adding a bunch of options to install/run the processors
> conditionally, handle non-.py files, skip the stdlib, etc. And I think the
> PEP is better without those options.
>
> > However, I think it *would* make sense to make the creation of a "Code
> > Transformation" HOWTO guide part of the PEP - having a guide means we
> > can clearly present the hierarchy in terms of:
>
> I like this idea.
>
> Earlier I suggested that the import system documentation should have some
> simple examples of how to actually use the import system to write
> transforming hooks. Someone (Brett?) pointed out that it's a dangerous
> technique, and making it too easy for people to play with it without
> understanding it may be a bad idea. And they're probably right.
>

If we added an appropriate warning to the example I would be fine adding
one that covers how to add a custom loader.

-brett



> A HOWTO is a bit more "out-of-the-way" than library or reference
> docs--and, more importantly, it also has room to explain when you shouldn't
> do this or that, and why.
>
> I'm not sure it has to be part of the PEP, but I can see the connection.
> While the PEP helps by separating out the most important safe case
> (semantically-neutral, reflected in .pyc, globally consistent, etc.), but
> it also makes the question "how do I do something similar to PEP 511
> transformers except ___" more likely to come up in the first place, making
> the HOWTO more important.
>
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