[IPython-dev] Input transformation rework - input requested

Tue May 29 09:19:13 EDT 2018

Looking at those links, Sage definitely does not restrict itself to valid
Python syntax. However, if there's only one downstream doing that, I think
it's reasonable for us to simplify the API and let Sage handle its own
preparsing. Does anyone know of any other projects which use input
transformations?

More specifically, I propose that we offer three transformation APIs:

1. Before handling our special syntax, to strip formatting like prompts
(accepts a cell as a string, returns transformed string)
2. After handling our special syntax, when the result should be valid
Python syntax, for things like wrapping floats (string -> string)
3. AST transformations (AST -> AST)

If projects like Sage want to, they could still transform invalid tokens in
hook 2, but their special syntax may interact unpredictably with our own.
Alternatively, they could copy and modify our transformation machinery to
handle their own special syntax. Either way, it avoids us having to
maintain a complex transformation interface which we may need to break
again.

Can I ask someone who's got a foot in the Sage camp to ping them about this
on their own lists?

Thomas

On 28 May 2018 at 17:41, Jason Grout <jason at jasongrout.org> wrote:

> It would be good to post separately to the Sage list. The code has changed
> since I was last in it, but I think these are the relevant bits:
>
> Register transforms: https://github.com/sagemath/sage/blob/
> 854f9764d14236110b8d7f7b35a7d52017e044f8/src/sage/repl/
> ipython_extension.py#L504-L513
>
> Preparsing: Defined at https://github.com/sagemath/sage/blob/
> 854f9764d14236110b8d7f7b35a7d52017e044f8/src/sage/repl/interpreter.py#L379,
> actual implementation at https://github.com/sagemath/sage/blob/
> 854f9764d14236110b8d7f7b35a7d52017e044f8/src/sage/repl/preparse.py
>
> Prompts: https://github.com/sagemath/sage/blob/
> 854f9764d14236110b8d7f7b35a7d52017e044f8/src/sage/repl/interpreter.py#L416
>
> There's also another transformation, it seems:
> https://github.com/sagemath/sage/blob/854f9764d14236110b8d7f7b35a7d5
> 2017e044f8/src/sage/repl/interpreter.py#L468
>
> Thanks,
>
> Jason
>
>
>
>
> On Mon, May 28, 2018 at 5:27 AM Thomas Kluyver <takowl at gmail.com> wrote:
>
>> Thanks Aaron. If working with valid Python syntax is sufficient, the API
>> will probably just be functions that take and return a string, leaving it
>> up to you how you tokenise/parse the code. We only need to do something
>> more complex if third-party transformations need to integrate with our own
>> ones to produce valid Python.
>>
>> Does anyone know what Sage does? Jason mentioned that they might also use
>> input transformations.
>>
>> On 28 May 2018 at 08:13, Aaron Meurer <asmeurer at gmail.com> wrote:
>>
>>> I believe you're right.
>>>
>>> I suppose another potential transform would be to allow x^2 to
>>> represent x**2. This would have be done at the token level since ^ has
>>> a different precedence than **.
>>>
>>> Only operating on valid Python seems fine. If someone wants to
>>> implement a DSL they should just write a kernel.
>>>
>>> Have you considered using something like parso, which can manipulate
>>> an AST and tokens losslessly?
>>>
>>> Aaron Meurer
>>>
>>> On Sun, May 27, 2018 at 11:50 PM, Thomas Kluyver <takowl at gmail.com>
>>> wrote:
>>> > Thanks Aaron. I am aware that Sympy uses input transformation, but it
>>> would
>>> > be good to check some more details of exactly how:
>>> >
>>> > 1. I believe wrapping integers and defining symbols can both be done
>>> with
>>> > AST transformations. Let me know if I'm missing something.
>>> > 2. Wrapping floats can't, because the string form is discarded before
>>> we get
>>> > the AST. But this is still an operation that changes one syntactically
>>> valid
>>> > piece of Python code to another, right? I'm considering limiting the
>>> API to
>>> > only operate on already valid Python code, and using private APIs to
>>> handle
>>> > IPython's special syntax (like %magics).
>>> > 3. Are there any other transformations that Sympy does (or wants to do)
>>> > besides these three?
>>> >
>>> > On 28 May 2018 at 00:02, Aaron Meurer <asmeurer at gmail.com> wrote:
>>> >>
>>> >> I'm sure you're already aware, but we use them for SymPy for some
>>> >> (optional) transformers that make Python more symbolic friendly
>>> >> (auto-replace undefined variables with Symbols, wrap integer literals
>>> >> with Integer so that exact rational numbers work, and so on). The AST
>>> >> transformer is nice but limiting. We can't use it to wrap float
>>> >> literals with higher precision for instance because Python drops the
>>> >> precision of floats in the AST.
>>> >>
>>> >> There are already some open issues about some limitations we've seen
>>> >> (https://github.com/sympy/sympy/issues/14440 and
>>> >> https://github.com/ipython/ipython/issues/10893). I'm not fully
>>> >> updated on the specifics of what the limitations were, but from what I
>>> >> remember, there were issues with IPython doing things line-by-line.
>>> >>
>>> >> I don't know how the new code is architected, but it would be nice if
>>> >> the transformers could just access the raw input from IPython, and
>>> >> various transformers could be plugged in to that to make things
>>> >> simpler if desired (the AST transformer could be one such instance).
>>> >>
>>> >> At the very least, if you want to test the new design, you could look
>>> >> at translating our transformers in SymPy (including the work in
>>> >> progress float transformer at
>>> >> https://github.com/sympy/sympy/pull/13300).
>>> >>
>>> >> Aaron Meurer
>>> >>
>>> >> On Sun, May 27, 2018 at 2:50 PM, Brian Granger <ellisonbg at gmail.com>
>>> >> wrote:
>>> >> > Thomas this is great news! I think that part of the code base could
>>> >> > benefit
>>> >> > from being simpler and more extensible. Thanks for tackling this!
>>> >> >
>>> >> > Sent from my iPhone
>>> >> >
>>> >> > On May 27, 2018, at 1:19 PM, Thomas Kluyver <takowl at gmail.com>
>>> wrote:
>>> >> >
>>> >> > Hi all,
>>> >> >
>>> >> > For IPython 7, I'm planning a rework of the input transformation
>>> >> > framework:
>>> >> > https://github.com/ipython/ipython/pull/11041
>>> >> >
>>> >> > The new framework is - I hope - simpler than the one it replaces,
>>> and
>>> >> > will
>>> >> > hopefully have fewer weird corner cases. But it's still a pretty
>>> complex
>>> >> > beast, and I don't feel like it's a good platform for people to add
>>> more
>>> >> > transformations to. One option to improve this is to make a smaller
>>> >> > extensible API, restricting the kind of things that third party
>>> code can
>>> >> > do.
>>> >> >
>>> >> > I don't think there's ever been much third party code extending
>>> >> > IPython's
>>> >> > input transformation, but I'd like to find out about the code that
>>> does.
>>> >> > So
>>> >> > if you're aware of a project that does use our input transformation
>>> API:
>>> >> >
>>> >> > - What project?
>>> >> > - What does it want to transform?
>>> >> > - Can you point me to the code?
>>> >> > - What fallback options would it have if IPython didn't support the
>>> >> > transformation it wanted?
>>> >> >
>>> >> > This is specifically about text transformations; AST
>>> transformations are
>>> >> > not
>>> >> > changed.
>>> >> >
>>> >> > Thanks,
>>> >> > Thomas
>>> >> >
>>> >> > _______________________________________________
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>>> >> > IPython-dev at python.org
>>> >> > https://mail.python.org/mailman/listinfo/ipython-dev
>>> >> >
>>> >> >
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