[Python-ideas] Positional only arguments

[Ron Adam]

Ron Adam wrote:
> Fred L. Drake, Jr. wrote:
>> On Thursday 17 May 2007, George Sakkis wrote:
>>  > single "delimiter" symbol (e.g. '%') between pos-only and pos-or-kw
>>  > would kill both birds with one stone, i.e. something like:
>>
>> A delimeter that would be needed anyway would make this a little nicer:
>>
>>   def myfunc(a, b, c=24; *, kw=42):
>>       pass
>>
>> This example would have 3 positional-only arguments (a, b, c) and one 
>> keyword-only argument (kw).
>>
>> Replacing the comma with a semicolon avoids the need for a syntax-only 
>> position (good, IMO), avoids introducing a new special character, and re-uses 
>> one that's rarely used anyway.
> 
> 
> [A few thoughts]
> 
>      def foo([positonal_only_args][; [kwd_args][; kwds_only]]): ...
 >
>      def myfunct(a, b, c=42; e=99; kw=42): ...

Hmmm, this has a problem if you use * or ** in the definition. :(

        def myfunc(*args;  ?  ; **kwds): ...


I think this would be an issue with some of the other ideas as well.


>      args = (1, 2, 3, 4)   # 'e' can be in either args or kwds,
>      kwds = {'kw': 42}     # but not both.
> 
>      bar = foo(*args, **kwds)
> 
> 
> How about signature objects that are similar to slice objects?
> 
>      sig = signature(*args, **kwds)      # Pre package signature.
>      sig = signature(1, 2, 3, 4, kw=42)
> 
> Could something like this have performance benefit if the same exact 
> signature is used over and over?  Possibly just passing a pre parsed name 
> space to the function?
> 
>      bar = foo(sig)        # No need to unpack with * or **.
> 
>      bar = foo(@sig)       # Be lenient, extra args and kwds
>                            # are consumed or ignored.
>                            # But always error if something is missing.
> 
> The '@' sign is like a vortex which sucks up unused args.  ;-)
> 
> Ron