[Python-Dev] Please reject or postpone PEP 526

[Nick Coghlan]

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

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

For ClassVar, you'd similarly want:


    class AnnotatedClassVariable:

        x: ClassVar[int]

to typecheck like "x" was declared as an annotated property on the metaclass.

Cheers,
Nick.

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