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

fwierzbicki at gmail.com fwierzbicki at gmail.com
Mon Aug 13 23:21:59 CEST 2012

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?

-Frank

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