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Fri Jun 22 22:58:40 CEST 2012 · https://mail.python.org/pipermail/python-dev/2012-June/120679.html

Yury Selivanov wrote:
> On 2012-06-22, at 3:47 PM, Ethan Furman wrote:
> 
>> Guido van Rossum wrote:
>>> On Fri, Jun 22, 2012 at 12:24 PM, Yury Selivanov
>>> <yselivanov.ml at gmail.com> wrote:
>>>> On 2012-06-22, at 3:18 PM, Guido van Rossum wrote:
>>>>
>>>>> On Fri, Jun 22, 2012 at 12:10 PM, Yury Selivanov
>>>>> <yselivanov.ml at gmail.com> wrote:
>>>>>> Yes, I meant optional.  Would 'name(arg1, *, [arg2])' be better?
>>>>> Hardly, because that's not valid syntax. I'd write name(arg1, *,
>>>>> arg2=<default>).
>>>> Like
>>>>
>>>>   replace(*, name=<default>, kind=<default>, default=<default>,
>>>>                                 annotation=<default>) -> Parameter
>>>>
>>>> or
>>>>
>>>>   replace(*, name=<optional>, kind=<optional>, default=<optional>,
>>>>                                 annotation=<optional>) -> Parameter
>>> Either one's an improvement, but you'll have to explain at the top of
>>> the PEP what you intend this notation to mean. I'd go with <optional>
>>> since the key thing here seems to be that various keywords, when not
>>> specified, mean that nothing changes. OTOH in some places you can
>>> probably write "foo=Signature.empty" (etc.).
>> Parameter names that follow '*' in the signature are not optional (unless that has changed since 3.2).  In other words, the above signature requires that name, kind, default, and annotation be specified by name *and* be given values when replace is called)
> 
> I know.  Those are optional keyword-only arguments.
> 
> In the code:
> 
>     def replace(self, *, name=_void, kind=_void, annotation=_void,
>                 default=_void):
> 
> We just need some clear convention for the PEP - and the <optional>
> mark should work.

That looks strange to me -- I suggest putting brackets around each one, 
like:

    replace(*, [name=<optional>,] [kind=<optional>,] 
[default=<optional>,] [annotation=<optional>]) -> Parameter

which is still a bit noisy.  At the risk of raising the ire of those who 
don't condone the use of '...' :)  how about:

    replace(*, [name=...,] [kind=...,] [default=...,] [annotation=...]
             ) -> Parameter

~Ethan~

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[Python-Dev] A Desperate Plea For Introspection (aka: BDFAP Needed)