[Python-ideas] Trial balloon: adding variable type declarations in support of PEP 484

[Neil Girdhar]

With PEP 520 accepted, would it be possible to iterate over 
__definition_order__?

class PrototypeNamedTuple:
    cache = {}
    def __new__(cls, *args):
        P = PrototypeNamedTuple
        if cls not in P.cache:
            P.cache[cls] = typing.NamedTuple(cls.__name__, 

[(definition, cls.__annotations__[definition])
for definition in cls.__definition_order__]

)
        return P.cache[cls](*args)

On Monday, August 8, 2016 at 5:09:50 PM UTC-4, Guido van Rossum wrote:
>
> Hm, overlooking the ordering is kind of a big deal for something with 
> "tuple" in its name. :-)
>
> Also it feels like it needs a metaclass instead of a cache.
>
> Maybe from this we can learn though that __anotations__ should be an 
> OrderedDict?
>
> On Mon, Aug 8, 2016 at 1:58 PM, אלעזר <ela... at gmail.com <javascript:>> 
> wrote:
>
>> class PrototypeNamedTuple:
>>     cache = {}
>>     def __new__(cls, *args):
>>         P = PrototypeNamedTuple
>>         if cls not in P.cache:
>>             P.cache[cls] = typing.NamedTuple(cls.__name__, 
>> cls.__annotations__.items())
>>         return P.cache[cls](*args)
>>
>> Works modulo ordering, though I'm not sure that's the right way to do it.
>>
>> The ordering part of namedtuple is orthogonal to the 
>> value-type/immutability part. So I would imagine making "Value" for the 
>> latter, "tuple" for the former, and namedtuple is mixing both (possibly 
>> given a convenient name, such as PrototypeNamedTuple). "Value" can also 
>> seen as mixing "Struct" and "Immutable", but that's overdoing it I guess.
>>
>> ~Elazar
>>
>> On Mon, Aug 8, 2016 at 11:25 PM Guido van Rossum <gu... at python.org 
>> <javascript:>> wrote:
>>
>>> That's a very interesting idea and one that deserves pursuing (though I 
>>> agree it's not a blocker for the PEP I'm hoping to write). I think the next 
>>> step is to prototype this -- which can only happen once we have an 
>>> implementation of the PEP. Though perhaps you could start by writing a 
>>> prototype that works by having the user write the following:
>>>
>>> class Starship(PrototypeNamedTuple):
>>>     damage = 0
>>>     captain = "Kirk"
>>>     __annotations__ = dict(damage=int, captain=str)
>>>
>>> It could also benefit from PEP 520 (Preserving Class Attribute 
>>> Definition Order).
>>>
>>> Who's game?
>>>
>>> --Guido
>>>
>>> On Mon, Aug 8, 2016 at 1:13 PM, אלעזר <ela... at gmail.com <javascript:>> 
>>> wrote:
>>>
>>>> class Starship:
>>>>>     stats: class Dict[str, int] = {}  # Pure class variable
>>>>>     damage: class int = 0  # Hybrid class/instance variable
>>>>>     captain: str  # Pure instance variable
>>>>>
>>>>
>>>> I can't avoid noting that there is an opportunity here to insert 
>>>> NamedTuple into the core language. The above example is almost there, 
>>>> except it's mutable and without convenient methods. But
>>>>
>>>> class Starship(tuple):
>>>>     damage: int = 0  
>>>>     captain: str  = "Kirk"
>>>>
>>>> Is an obvious syntax for 
>>>>
>>>>     Starship = NamedTuple('Starship', [('damage', int), ('captain', 
>>>> str)])
>>>>
>>>> Only much more available and intuitive to read, use, and of course - 
>>>> type check.
>>>> (Of course, it does mean adding semantics to the declaration syntax in 
>>>> general)
>>>>
>>>> I'm not really suggesting to make this change now, but I believe it 
>>>> will be done, sooner or later. My brief experience with mypy convinced me 
>>>> that it must be the case. The new declaration syntax only makes it easier.
>>>>
>>>> ~Elazar
>>>>
>>>> _______________________________________________
>>>> Python-ideas mailing list
>>>> Python... at python.org <javascript:>
>>>> https://mail.python.org/mailman/listinfo/python-ideas
>>>> Code of Conduct: http://python.org/psf/codeofconduct/
>>>>
>>>
>>>
>>>
>>> -- 
>>> --Guido van Rossum (python.org/~guido)
>>>
>>
>
>
> -- 
> --Guido van Rossum (python.org/~guido)
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.python.org/pipermail/python-ideas/attachments/20160809/f53cb860/attachment-0001.html>