[Python-ideas] New 3.x restriction on number of keyword arguments

Cesare Di Mauro cesare.di.mauro at gmail.com
Tue Oct 26 13:10:56 CEST 2010

2010/10/26 M.-A. Lemburg <mal at egenix.com>

> Cesare Di Mauro wrote:
>  > I can provide another patch that will not use EXTENDED_ARG (no VM
> changes),
> > and uses *args and/or **kwargs function calls when there are more than
> 255
> > arguments or keyword arguments.
> >
> > But I need some days.
> >
> > If needed, I'll post it at most on this week-end.
> You mean a version that pushes the *args tuple and **kws dict
> on the stack and then uses those for calling the function/method ?
> I think that would be a lot more efficient than pushing/popping
> hundreds of parameters on/off the stack.
> --
>  Marc-Andre Lemburg

I was referring to the solution (which I prefer) that I proposed answering
to Greg, two days ago.

Unfortunately, the stack must be used whatever the solution we will use.

Pushing the "final" tuple and/or dictionary is a possible optimization, but
we can use it only when we have a tuple or dict of constants; otherwise we
need to use the stack.

Good case:  f(1, 2, 3, a = 1, b = 2)
We can push (1, 2, 3) tuple and {'a' : 1, 'b' : 2}, then calling f with
CALL_FUNCTION_VAR_KW opcode passing narg = nkarg = 0.

Worst case: f(1, x, 3, a = x, b = 2)
We can't push the tuple and dict as a whole, because they need first to be
built using the stack.

The good case is possible, and I have already done some work in wpython
collecting constants on parameters push (even partial constant sequences),
but some additional work must be done recognizing costants-only tuple /

However, the worst case rest unresolved.

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