On Mon, Jan 11, 2021 at 5:21 PM Larry Hastings <la...@hastings.org> wrote:
>
> On 1/11/21 4:39 PM, Guido van Rossum wrote:
>
> The easiest thing would be just to create an empty `__annotations__` for
> classes that have no annotated variables, and to hell with the cost.
>
> I assume you'd keep the existing behavior where functions lazy-create an
> empty dict if they have no annotations too?
>
Indeed -- that's trying to provide a uniform interface.
> That all would work fine and be consistent, but you'd probably have to set
> the empty __annotations__ dict on modules too. I've noticed that code that
> examines annotations tends to handle two classes of objects: "functions"
> and "not-functions". Modules also store their __annotations__ in their
> __dict__, so the same code path works fine for examining the annotations of
> both classes and modules.
>
I'm not against giving all modules an empty `__annotations__` by default.
>
> (I noticed that `__slots__` is missing from your list. Maybe because it
> follows yet another pattern?)
>
> I forgot about __slots__! Yup, it's optional, and you can even delete it,
> though after the class is defined I'm not sure how much difference that
> makes.
>
> Slots intelligently support inheritance, too. I always kind of wondered
> why annotations didn't support inheritance--if D is a subclass of C, why
> doesn't D.__annotations__ contain all C's annotations too? But we're way
> past reconsidering that behavior now.
>
Anyway, `__slots__` doesn't behave that way -- seems it behaves similar to
`__annotations__`.
```
Python 3.9.1 (tags/v3.9.1:1e5d33e, Dec 7 2020, 17:08:21) [MSC v.1927 64
bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> class A: __slots__ = ['a']
...
>>> class B(A): __slots__ = ['b']
...
>>> B.__slots__
['b']
>>> class X(A): pass
...
>>> X.__slots__
['a']
>>> A().__dict__
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
AttributeError: 'A' object has no attribute '__dict__'
>>> X().__dict__
{}
>>>
```
--
--Guido van Rossum (python.org/~guido)
*Pronouns: he/him **(why is my pronoun here?)*
<http://feministing.com/2015/02/03/how-using-they-as-a-singular-pronoun-can-change-the-world/>
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