[Python-Dev] [compatibility-sig] do all VMs implement the ast module? (was: Re: AST optimizer implemented in Python)

[Brett Cannon]

On Aug 13, 2012 5:22 PM, "fwierzbicki at gmail.com" <fwierzbicki at gmail.com>
wrote:
>
> On Mon, Aug 13, 2012 at 1:46 PM, Guido van Rossum <guido at python.org>
wrote:
> > On Mon, Aug 13, 2012 at 1:05 PM, fwierzbicki at gmail.com
> > <fwierzbicki at gmail.com> wrote:
> >> On Mon, Aug 13, 2012 at 12:06 PM, Brett Cannon <brett at python.org>
wrote:
> >>>> I see nothing about ast possibly being CPython only. Should there be?
> >>>
> >>>
> >>> Time to ask the other VMs what they are currently doing (the ast
module came
> >>> into existence in Python 2.6 so all the VMs should be answer the
question
> >>> since Jython is in alpha for 2.7 compatibility).
> >
> > [Jython]
> >> 2.5+ contains an ast.py that I obsessively compared to CPython's 2.5
> >> ast.py.
> >
> > But CPython's ast.py contains very little code -- it's all done in
ast.c.
> What I did was dump a pretty print of the ast from Jython and CPython
> for every file in Lib/* and diff the results with a script. I got the
> differences down to a small number of minor variations.
>
> > Still, I'm glad you are actually considering this a cross-language
> > feature, and I will gladly retract my warning. (Still, I don't know if
> > it is subject to the usual backward compatibility constraints.)
> I don't know if IronPython does the same though... we might want to
> wait for them to respond.
>
> > It might be pure python for Jython, but it's not for CPython.
> It's actually Java for us :) -- in fact the internal AST uses the
> exact Java that is exposed from our _ast.py - which I've come to
> regard as a mistake (though it was useful at the time). I want to do
> the same obsessive diff game with 3.x but then probably separate out
> our internal ast implementation (possibly making ast.py pure Python).
>
> BTW - is Python's internal AST exactly exposed by ast.py or is there a
> separate internal AST implementation?

Direct. There is an AST grammar file that gets compiled into C and Python
objects which are used by the compiler (c version) or exposed to users
(Python version).

>
> -Frank
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