There are three particular items I have in mind, but a general question.
(1) There is currently a thread about using overload for single or multiple dispatch. I think a better solution would be to allow users to declare their dispatching decorators as having overload semantics.
(2) Under sqlalchemy, hybrid_property is a commonly used decorator with property-like meaning. Other libs have similar decorators, and all of their usages require the same workaround.
(3) PEP 724 / StrictTypeGuard aligns user defined guards more closely with isinstance. However, a comment in the discussion thread notes that isinstance has some special treatment in type checkers. That means that even with StrictTypeGuard, there could still be some gap between the two.
Most of us are familiar with a typical workaround for these cases. In terms of (2),
if TYPE_CHECKING: hybrid_property = property else: from sqlalchemy.orm import hybrid_property
To some, I’m sure that seems fine. At typing time, use one, and at runtime, use the other.
To me, this looks like a “hack” to handle the fact that we cannot correctly declare user-defined constructs with the typing-time behavior of certain special symbols.
And in terms of (1), it won’t work nicely. Overload usage expects a non-overloaded variant, which is not a good interface requirement for dispatch systems.
Are the typing maintainers of one mind or the other regarding these cases? Is each one different, with some being good ideas and others not?
I’m sure isinstance’s special cases are tied to iterables and tuples of types. Perhaps that’s the only way in which it differs from StrictTypeGuard. Can it be retconned in typing docs and specifications to be described that way? “isinstance behaves as a StrictTypeGuard when used on a single type, of the form
type[T] -> StrictTypeGuard[T]”?
This seems like a common problem with a potentially common solution: try to make the special constructs in the language less special and more user-available.
My main question is: is this a fruitful area to discuss and explore? When I find such things, should I be thinking that it’s a problem which typing can solve, or is that “just the way it is” and I will forever be using the typing-time aliasing trick?