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

Terry Reedy tjreedy at udel.edu
Mon Aug 13 23:27:28 CEST 2012

On 8/13/2012 4:46 PM, Guido van Rossum 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.
> 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 should have quoted a bit more. After the first sentence
"The ast module helps Python applications to process trees of the Python 
abstract syntax grammar."
the next sentence is
"The abstract syntax itself might change with each Python release; this 
module helps to find out programmatically what the current grammar looks 

The 'current grammar' is given in 30.2.2. Abstract Grammar.

Terry Jan Reedy

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