[Python-Dev] Positional-only parameters in Python

[Guido van Rossum]

On Fri, Jan 19, 2018 at 8:47 PM, Nick Coghlan <ncoghlan at gmail.com> wrote:

> On 20 January 2018 at 07:49, Mario Corchero <mariocj89 at gmail.com> wrote:
> > I am happy to put some work into this (and Pablo Galindo in CC offered to
> > pair on it) but it is not clear for me whether the next step is drafting
> a
> > new PEP or this is just blocked on "re-evaluating" the current one.
>
> I think that would be a question for Larry,
>

I think you meant for Guido. It's not Larry's language (yet :-).


> since there are two main options here:
>
> - proposing just the "/" part of PEP 457 (which allows positional-only
> arguments, but doesn't allow the expression of all builtin and
> standard library signatures)
> - proposing the full PEP 547,
>

I assume you meant PEP 457 again. :-)


> including the "argument groups" feature
> (which is a bigger change, but allows the expression of signatures
> like "range([start,] stop, [step,] /)")
>
> One key benefit I'd see to a new subset-of-457 PEP is that it would
> allow a decision to be made on the basic "/" proposal without deciding
> one way or the other on whether or not to provide a native way to
> express signatures like the one for range().


I personally don't think such signatures are common enough to warrant
special syntax, and I don't want to encourage them. The few we have
(basically range(), slice() and a few functions in the curses module) don't
inspire a lot of copy-cat APIs.

OTOH the more plain positional-only arguments are a pretty common need --
for example, for methods that are conventionally used that way, and
overridden with disregard for argument names.

(IOW I agree with you here. ;-)

-- 
--Guido van Rossum (python.org/~guido)
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