On Feb 14, 11:13 pm, "Guido van Rossum" <[EMAIL PROTECTED]> wrote:
> On Thu, Feb 14, 2008 at 2:48 PM, Raymond Hettinger <[EMAIL PROTECTED]> wrote:
> > I've been exercising the new keyword-only arguments syntax. It is
> > absolutely wonderful. I'm amazed at how many long standing problems it
> > solves elegantly.
>
> Agreed. Now can you come up with a syntax for positional-only
> arguments? So far everybody has failed at that, and there are some use
> cases where it's useful too.
The idea in PEP 3102 is that *args gobbles up all remaining positional
arguments, hence what comes after can only be interpreted as
keyword-only arguments. This is extended to allowing * on its own.
e.g. f(*, z, t=2)
=> z, t are keyword-only
Following the same train of thought, **kwargs gobbles up all remaining
keyword arguments, hence what comes after can only interpreted as
positional-only arguments. Then one could extend it to allowing ** on
its own.
e.g. f(**, x, y=1)
=> x, y are positional-only
Now, how do keyword-only arguments fit in? Say x, y=1 are
positional-only and z, t=2 are keyword-only. One could have:
f(**, x, y=1, *, z, t=2)
The general cases could look like
f(x, y=1, *args, z, t=2, **kwargs):
=> x, y are hybrid
=> args: all remaining positional arguments
=> z, t are keyword-only
=> kwargs: all remaining keyword arguments
f(**kwargs, x, y=1, *args, z, t=2):
=> x, y are positional-only
=> args: all remaining positional arguments
=> z, t are keyword-only
=> kwargs: all remaining keyword arguments
'args' and 'kwargs' are optional in both cases. If 'kwargs' is present
in the second version, it is a bit strange as it usually only appears
at the end. Alternatively, only '**' could be allowed at the start
and if needed '**kwargs' would come at the end:
f(**, x, y=1, *args, z, t=2, **kwargs)
Note that this syntax doesn't allow for positional-only and hybrid
arguments to coexist. But this is nice IMHO, as it seems to me that
it would only create confusion.
Unconvincingly yours,
--
Arnaud
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