[Python-Dev] Please reject or postpone PEP 526

[Koos Zevenhoven]

On Mon, Sep 5, 2016 at 5:02 PM, Nick Coghlan <ncoghlan at gmail.com> wrote:
> On 5 September 2016 at 23:46, Nick Coghlan <ncoghlan at gmail.com> wrote:
>> Under such "parameter annotation like" semantics, uninitialised
>> variable annotations would only make sense as a new form of
>> post-initialisation assertion,

Why not discuss this in the python-ideas thread where I quote myself
from last Friday regarding the notion of annotations as assertions?

>> and perhaps as some form of
>> Eiffel-style class invariant documentation syntax.

I hope this is simpler than it sounds :-)

> Thinking further about the latter half of that comment, I realised
> that the PEP 484 equivalence I'd like to see for variable annotations
> in a class body is how they would relate to a property definition
> using the existing PEP 484 syntax.
>
> For example, consider:
>
>     class AnnotatedProperty:
>
>         @property
>         def x(self) -> int:
>             ...
>
>         @x.setter
>         def x(self, value: int) -> None:
>             ...
>
>         @x.deleter
>         def x(self) -> None:
>             ...
>
> It would be rather surprising if that typechecked differently from:
>
>     class AnnotatedVariable:
>
>         x: int
>

How about just using the latter way? That's much clearer. I doubt this
needs a change in the PEP.

> For ClassVar, you'd similarly want:
>
>
>     class AnnotatedClassVariable:
>
>         x: ClassVar[int]
>
> to typecheck like "x" was declared as an annotated property on the metaclass.
>

Sure, there are many things that one may consider equivalent. I doubt
you'll be able to list them all in a way that everyone agrees on. And
I hope you don't take this as a challenge -- I'm in the don't-panic
camp :).


-- Koos


> Cheers,
> Nick.
>
> --
> Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia



-- 
+ Koos Zevenhoven + http://twitter.com/k7hoven +