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

[Guido van Rossum]

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 <elazarg at gmail.com> 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 <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)
>>
>


-- 
--Guido van Rossum (python.org/~guido)
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