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

[Sven R. Kunze]

On 28.01.2016 18:03, Victor Stinner wrote:
> I don't understand your question.
>
> I guess that your real question is: are stdlib modules loaded with
> peephole optimizer enabled or not?
>
> If you use -o noopt, you are safe: the peephole optimizer is disabled
> before the first Python import.
>
> If you use sys.set_code_transformers([]) in your code, it's likely
> that Python already imported 20 or 40 modules during its
> initialization (especially in the site module).
>
> It's up to you to pick the best option. There are different usages for
> each option. Maybe you just don't care of the stdlib, you only want to
> debug your application code, so it's doesn't matter how the stlidb is
> optimized?
>
> --
>
> Or are you asking me to remove sys.set_code_transformers([]) from the
> section "Usage 3: Disable all optimization"? I don't understand.
That is exactly the issue with setting a transformer at runtime which I 
don't understand. That is one weakness of the PEP; some people already 
proposed to make a difference between

- local transformation
- global transformation

I can understand the motivation to have the same API for both, but's 
inherently different and it makes talking about it hard (as we can see 
now). I would like to have this clarified in the PEP (use consistent 
wording) or even split it up into two different parts of the PEP.


You said I would need to call the function before all imports. Why is 
that? Can I not call it it twice in the same file? Or in a loop? What 
will happen? Will the file get recompiled each time? Some people 
proposed a "from __extensions__ import my_extension"; inspired by 
__future__ imports, i.e. it is forced to be at the top. Why? Because it 
somehow makes sense to perform all transformations the first time a file 
is loaded. I don't see that addressed in the PEP. I have to admit I 
would prefer this kind usage over a function call.

Furthermore:
- we already have import hooks. They can be used for local 
transformation. I don't see that addressed in the PEP.
- after re-reading the PEP I have some difficulties to see how to 
activate, say, 2 custom transformers **globally** (via -o). Maybe, 
adding an example would help here.