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

[אלעזר]

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 <guido at python.org> 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 <elazarg at gmail.com> 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
>>
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>>
>
>
>
> --
> --Guido van Rossum (python.org/~guido)
>
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