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 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-imp...

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 _______________________________________________ Python-Dev mailing list -- python-dev@python.org To unsubscribe send an email to python-dev-leave@python.org https://mail.python.org/mailman3/lists/python-dev.python.org/ Message archived at https://mail.python.org/archives/list/python-dev@python.org/message/RZYDHYZP... Code of Conduct: http://python.org/psf/codeofconduct/

On Fri, 16 Oct 2020, 23:04 Stefano Borini, 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-imp...

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.

Have you manually checked that the generated source in pegen.c contains your changes? You should be able to see by just looking for calls to _Py_Subscript, or other code snippets from the modified grammar. Or, you can introduce an error in the grammar's code snippets and check that you get the expected error. FWIW, I found I had to explicitly regenerate pegen.c with 'make regen-pegen'; 'make regen-all' wasn't enough.

Thanks

-- Kind regards,

Stefano Borini _______________________________________________ Python-Dev mailing list -- python-dev@python.org To unsubscribe send an email to python-dev-leave@python.org https://mail.python.org/mailman3/lists/python-dev.python.org/ Message archived at https://mail.python.org/archives/list/python-dev@python.org/message/RZYDHYZP... Code of Conduct: http://python.org/psf/codeofconduct/