[Pyrex] Trailing comma in def argument list not accepted in Pyrex (with patch)

[Robert Bradshaw]

I agree this should be fixed and your proposed patch looks sound.  
I've changed it in SageX, it will be there in the next release.

Thanks,
Robert

On Jun 17, 2007, at 3:35 PM, Jim Kleckner wrote:

> Note that Python permits an argument list to end with an empty
> argument but Pyrex does not.  The argument list is a tuple and
> tuples are permitted to end with a trailing comma.  In fact, a
> tuple of one element must have a comma to syntactically
> differentiate parenthesized expressions from tuples.
>
> Would it make sense to permit this in Pyrex and Sagex?
>
> I have a ton of code with trailing commas in def argument
> lists...  Part of the reason is that adding or deleting an
> argument definition can be done by adding or deleting a whole
> line by itself in Python.  With Pyrex, you have to remember to
> edit the previous line to add a comma.  e.g.:
> def foo(
>      arg1=None,
>      arg2=None,
>      arg3=None,
>      arg4=None,  # In Pyrex, this causes a missing argument error
> ):
>      pass
>
>
> ================ Example:
> def foo(arg1, arg2,):
>    return arg1 + arg2
>
> ================ Pyrex 0.9.5.1a output
> /cygdrive/c/Jim/dev/runsim/finsim/playpyrex/hello.pyx:2:19: Missing
> argument name
>
> ================ Sagex output
>
> Error converting Pyrex file to C:
> ------------------------------------------------------------
> ...
>
> def foo(arg1, arg2,):
>                    ^
> ------------------------------------------------------------
>
> /cygdrive/c/Jim/dev/runsim/finsim/playpyrex/hello.pyx:2:19: Missing
> argument name
>
> ================ Patch discussion:
>
> [I now use the sagex version of Pyrex because of the increased
> speed and better error reporting.]
>
> After perusing the code, it seems to me that the following code
> change to Parsing.py would effect the change.  But someone would
> need to try it out with all the test cases and someone more
> knowledgeable should assess whether this breaks something else.
>
> In the code below, simply change the use of c_arg_list_trailers
> to c_arg_list_terminators.  Since trailers was defined for a
> reason, this is probably not the whole story, but just the place
> for the surgeon to place the scalpel...
>
> And yes, I know, the patch is not in standard form.
> But it is just one line...
>
> ================ Patch candidate:
> c_arg_list_terminators = ('*', '**', '.', ')')
> c_arg_list_trailers = ('.', '*', '**')
>
> def p_c_arg_list(s, in_pyfunc, cmethod_flag = 0):
>      args = []
>      if s.sy not in c_arg_list_terminators:
>          args.append(p_c_arg_decl(s, in_pyfunc, cmethod_flag))
>          while s.sy == ',':
>              s.next()
> # JEK: The use of c_arg_list_trailers fails to recognize ')' as end of
> arg list.
> # JEK:      if s.sy in c_arg_list_trailers:
>              if s.sy in c_arg_list_terminators:
>                  break
>              args.append(p_c_arg_decl(s, in_pyfunc))
>      return args
>
>
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