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[Python-ideas] Keyword-only arguments?

Guido van Rossum guido at python.org
Wed Jun 17 21:29:31 CEST 2015 
It's used all over the asyncio code.

On Wed, Jun 17, 2015 at 9:11 PM, Amber Yust <amber.yust at gmail.com> wrote:

> Interesting. I don't think I've ever seen it used, even having looked at
> Python 3 code. For those who have worked with more Python 3 code than I
> have, do you ever see it used?
>
> On Wed, Jun 17, 2015 at 12:02 PM Chris Kaynor <ckaynor at zindagigames.com>
> wrote:
>
>> On Wed, Jun 17, 2015 at 11:58 AM, Amber Yust <amber.yust at gmail.com>
>> wrote:
>>
>>> One thing that has been a source of bugs and frustration in the past is
>>> the inability to designate a named keyword argument that cannot be passed
>>> as a positional argument (short of **kwargs and then keying into the dict
>>> directly). Has there been any previous discussion on the possibility of a
>>> means to designate named arguments as explicitly non-positional?
>>>
>>> Not a solid proposal, but to capture the essential difference of what
>>> I'm thinking of, along the lines of...
>>>
>>>     def foo(bar, baz=None, qux: None):
>>>
>>> where bar is a required positional argument, baz is an optional argument
>>> that can have a value passed positionally or by name, and qux is an
>>> optional argument that must always be passed by keyword.
>>>
>>> Such a means would help avoid cases where a misremembered function
>>> signature results in a subtle and likely unnoticed bug due to unintended
>>> parameter/argument mismatch.
>>>
>>> (It's possible that this has been discussed before - a cursory search of
>>> python-ideas didn't bring up any direct discussion, but I may have missed
>>> something. If you have a link to prior discussion, please by all means
>>> point me at it!)
>>>
>>
>> This feature was added to Python 3 about 9 years ago, see
>> https://www.python.org/dev/peps/pep-3102/. A quick search for "python
>> keyword only arguments" on Google found it.
>>
>> Guido's time machine strikes again!
>>
>> Chris
>>
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>
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-- 
--Guido van Rossum (python.org/~guido)
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