[Python-Dev] Enable access to the AST for Python code

[Ben Hoyt]

Heh, thanks. :-)

On Thu, May 21, 2015 at 2:17 PM, Guido van Rossum <guido at python.org> wrote:

> Dang it. :-) I just want to encourage you to continue pursuing this idea,
> one way or another.
>
> On Thu, May 21, 2015 at 7:01 AM, Ben Hoyt <benhoyt at gmail.com> wrote:
>
>> Thanks. Good point about python-ideas -- I was thinking that after I sent
>> it too. I'll repost there soon.
>>
>> Out of interest, what specifically were you referring to as "definitely
>> cool" here: LINQ-style generator expressions that build SQL ala PonyORM, or
>> the more general feature of enabling AST access?
>>
>> -Ben
>>
>> On Wed, May 20, 2015 at 10:31 PM, Guido van Rossum <guido at python.org>
>> wrote:
>>
>>> Hey Ben, this is probably a better topic for python-ideas. I'll warn you
>>> that a hurdle for ideas like this is that ideally you don't want to support
>>> this just for CPython. It's definitely cool though! (Using movie poster
>>> style quotes you can turn this into a ringing endorsement: "definitely
>>> cool" -- The BDFL. :-)
>>>
>>> On Wed, May 20, 2015 at 7:26 PM, Ben Hoyt <benhoyt at gmail.com> wrote:
>>>
>>>> Hi Python devs,
>>>>
>>>> Enabling access to the AST for compiled code would make some cool
>>>> things possible (C# LINQ-style ORMs, for example), and not knowing too
>>>> much about this part of Python internals, I'm wondering how possible
>>>> and practical this would be.
>>>>
>>>> Context: PonyORM (http://ponyorm.com/) allows you to write regular
>>>> Python generator expressions like this:
>>>>
>>>>     select(c for c in Customer if sum(c.orders.price) > 1000)
>>>>
>>>> which compile into and run SQL like this:
>>>>
>>>>     SELECT "c"."id"
>>>>     FROM "Customer" "c"
>>>>     LEFT JOIN "Order" "order-1" ON "c"."id" = "order-1"."customer"
>>>>     GROUP BY "c"."id"
>>>>     HAVING coalesce(SUM("order-1"."total_price"), 0) > 1000
>>>>
>>>> I think the Pythonic syntax here is beautiful. But the tricks PonyORM
>>>> has to go to get it are ... not quite so beautiful. Because the AST is
>>>> not available, PonyORM decompiles Python bytecode into an AST first,
>>>> and then converts that to SQL. (More details on all that from author's
>>>> EuroPython talk at http://pyvideo.org/video/2968)
>>>>
>>>> I believe PonyORM needs the AST just for generator expressions and
>>>> lambda functions, but obviously if this kind of AST access feature
>>>> were in Python it'd probably be more general.
>>>>
>>>> I believe C#'s LINQ provides something similar, where if you're
>>>> developing a LINQ converter library (say LINQ to SQL), you essentially
>>>> get the AST of the code ("expression tree") and the library can do
>>>> what it wants with that.
>>>>
>>>> What would it take to enable this kind of AST access in Python? Is it
>>>> possible? Is it a good idea?
>>>>
>>>> -Ben
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>>>
>>>
>>>
>>> --
>>> --Guido van Rossum (python.org/~guido)
>>>
>>
>>
>
>
> --
> --Guido van Rossum (python.org/~guido)
>
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