[Python-Dev] Please reject or postpone PEP 526 (original) (raw)

Koos Zevenhoven k7hoven at gmail.com
Mon Sep 5 10:24:15 EDT 2016

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

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