That's what I suspected looking at the parser debug in fact. Good to
see that I was on the right track. Thanks! I'll play with it a bit
more tonight.
On Fri, 16 Oct 2020 at 23:43, Pablo Galindo Salgado <pablog...@gmail.com> wrote:
>
> Hi Stefano,
>
> One of the problems you have is that the rule for slices has a negative
> lookahead for the comma:
>
> slices[expr_ty]:
> | a=slice !',' { a }
>
> IIRC the reason that is there is to allow "x[3,]" to be parsed.
>
> Also, to allow "a[k=3]" you need to to create a rule that allows skipping the
> "slices" part of the subscript and allow the 2nd argument of _Py_Subscript
> to be NULL. For example:
>
> | a=t_primary '[' k=kwargs ']' !t_lookahead { _Py_Subscript(a, NULL, k,
> Store, EXTRA) }
>
> Regards,
> Pablo
>
> On Fri, 16 Oct 2020 at 22:07, Stefano Borini <stefano.bor...@gmail.com> wrote:
>>
>> Hello,
>>
>> I am trying to implement PEP-637, and I started modifying the parser
>> and the grammar, but I don't know what I am missing.
>>
>> The PR is here
>>
>> https://github.com/python/cpython/compare/master...stefanoborini:PEP-637-implementation-attempt-1?expand=1
>>
>> It includes other stuff but the core is that I extended the Subscript
>> in the asdl to accept the keyword args
>>
>> | Subscript(expr value, expr slice, keyword* keywords, expr_context ctx)
>>
>> which seems to work:
>>
>> >>> ast.parse('a[3]').body[0].value.keywords
>> []
>>
>> I also added a few "productions" (I believe they are called like this,
>> my compiler theory is very approximated), one of which is now
>>
>> primary[expr_ty]:
>> ....
>> | a=primary '[' b=slices c=[',' k=kwargs {k}]']' {
>> _Py_Subscript(a, b, c, Load, EXTRA) }
>>
>> I also tried with additional formats like
>>
>> | a=primary '[' b=slices c=kwargs ']' { _Py_Subscript(a, b, c,
>> Load, EXTRA) }
>>
>> or even just
>>
>> | a=primary '[' c=kwargs ']' { _Py_Subscript(a, NULL, c, Load, EXTRA) }
>>
>> but I always get a SyntaxError:
>>
>> >>> ast.parse('a[k=3]').body[0].value.keywords
>> Traceback (most recent call last):
>> File "<stdin>", line 1, in <module>
>> File "/Users/sbo/Work/Projects/stefanoborini/cpython/Lib/ast.py",
>> line 50, in parse
>> return compile(source, filename, mode, flags,
>> File "<unknown>", line 1
>> a[k=3]
>> ^
>> SyntaxError: invalid syntax
>>
>> Note that I always recreated ast parser and pegen.c with 'make
>> regen-all' and recompiled with make.
>> I tried to enable debug and print the pegen.c debug, but it's a bit
>> heavy and I could not immediately spot the issue. I suspect I am
>> missing something somewhere.
>>
>> Thanks
>>
>>
>> --
>> Kind regards,
>>
>> Stefano Borini
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--
Kind regards,
Stefano Borini
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