[Python-ideas] Short form for keyword arguments and dicts

[Anders Hovmöller]

The *locals(...) thing looks pretty nice and would clearly take away a lot of the pain I was talking about! Thanks

> On 26 Jun 2013, at 16:46, Joshua Landau <joshua.landau.ws at gmail.com> wrote:
> 
>> On 26 June 2013 09:04, Ethan Furman <ethan at stoneleaf.us> wrote:
>>> On 06/26/2013 12:48 AM, Greg Ewing wrote:
>>> 
>>> Ron Adam wrote:
>>>> 
>>>> And I don't like the '=' with nothing on the right.
>>> 
>>> 
>>> Expanding on the suggestion someone made of having a
>>> single marker of some kind in the argument list, I
>>> came up with this:
>>> 
>>>     def __init__(self, text, font = system_font, style = 'plain'):
>>>        default_size = calc_button_size(text, font, style)
>>>        Widget.__init__(self, size = default_size, pass font, style)
>> 
>> 
>> I don't care for it.
>> 
>> A word doesn't stand out like a character does, plus this usage of pass is
>> completely different from its normal usage.
>> 
>> We're already used to interpreting '*' as a coin with two sides, let's stick
>> with it:
>> 
>>    def apply_map(map, target, *, frobble):  # '*' means frobble is keyword
>> only
>>       ...
>> 
>> and later:
>> 
>>    frobble = some_funny_stuff_here()
>>    .
>>    .
>>    .
>>    apply_map(map=kansas, target=toto, *, frobble) # '*' means frobble maps
>> to keyword frobble
> 
> Whilst Greg Ewing has made me also much more sympathetic to this view,
> I feel that:
> 
> 1) This is nearly unreadable - it does not say what it does in the slightest
> 
> 2) It's added syntax - that's a high barrier. I'm not convinced it's
> worth it yet.
> 
> 3) It still feels like hackery; I might prefer something explicitly
> hackery like this:
> 
>    apply_map(map=kansas, target=toto, **locals("frobble"))
> 
> where locals is:
> 
>    def locals(*args):
>        if args:
>            return {arg:original_locals()[arg] for arg in args}
>        else:
>            return original_locals()
> 
> For Greg's he'd use:
> 
>   def __init__(self, text="Hello", font=system_font, **kwds):
>            default_size = calc_default_size(text, font)
>            Widget.__init__(self, size=default_size, **locals("font"), **kwds)
> 
> or even
> 
>   def __init__(self, text = "Hello", font = system_font, **kwds):
>            default_size = calc_default_size(text, font)
>            Widget.__init__(self, **locals("size", "font"), **kwds)
> 
> under the asumption that http://bugs.python.org/issue2292 does get
> implemented first.
> 
> For reference, he is using (respaced for consistency):
> 
>        def __init__(self, text="Hello", font=system_font, **kwds):
>            default_size = calc_default_size(text, font)
>            Widget.__init__(self, size=default_size, font=font, **kwds)
> 
> Note that this is only a way to suggest that *there might be another
> way*; maybe something involving objects.
> 
> 3 cont.) The reason I think it feels like hackery is simply that I
> don't feel like Python is ever "reference by name"; objects don't know
> what they are called (some know what they *were* named; but they have
> no guarantee it's true) it feels *very wrong* to give "foobar" to
> function and have that function somehow extract the name! I know it's
> not doing that, but it's ever-so-close.
> 
> However; maybe:
> 
>    class AttrDict(dict):
>        def __init__(self, mapping, **defaults):
>            super().__init__(defaults, **mapping)
>            self.__dict__ = self
> 
>    def __init__(self, **kwds):
>        kwds = AttrDict(kwds, text="Hello", font=system_font)
> 
>        kwds.size = calc_default_size(kwds.text, kwds,font)
> 
>        Widget.__init__(self, **kwds)
> 
> and a decorator could even make this:
> 
>    @dynamic_kwds(text="Hello", font=system_font)
>    def __init__(self, kwds):
>        kwds.size = calc_default_size(kwds.text, kwds,font)
>        Widget.__init__(self, **kwds)
> 
> which would have the same run-time effect as the original (the second
> keeps re-evaluating the signature).
> 
> 
> Again; I mention these only to show people not to have a restricted
> idea on what the solution looks like - don't just try and fix the
> symptoms of the problem.
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