[Python-3000] PEP 3102 comments

[Baptiste Carvello]

>  > Here's a related but more complicated wish: define a function in such
>  > a way that certain parameters *must* be passed as keywords, *without*
>  > using *args or **kwds. This may require a new syntactic crutch.
> 
> While a number of people have submitted possible use cases for this 
> feature, others have challenged the validity of such cases.
> 
> At this point, I don't feel that the use cases for part 2 of the PEP are 
> as well-understood as the use cases for part 1.
> 

maybe those use cases can work without syntactic sugar. With only part 1, you 
can already add a manual check if you need:

 >>> def myfunction(a1, a2, *forbidden, kw1, kw2):
...    assert forbidden is (), "myfunction() takes exactly 2 arguments"
...    pass
 >>>

If you want to have access to the function itself (to modify the signature), you 
can use a decorator:

 >>> @forbid('forbidden')
 >>> def myfunction(a1, a2, *forbidden, kw1, kw2):
...    pass
 >>>

(there can be a hook in the function object that @forbid will call, which would 
both fix the signature and add the runtime check)

or, some time in the future, a typecheck:

 >>> @forbid_moreargs
 >>> def myfunction(a1, a2, *forbidden : Forbidden, kw1, kw2):
...    pass
 >>>

(where Forbidden is a marker object)

As long as we have an agreed upon idiom, it is not really important if it takes 
on more line. Personnaly, I find any of those far more explicit that the lone 
start thinggy.

Baptiste