Easy way to get common types for annotations

[Dreamsorcerer]

🐣 Is your feature request related to a problem? Please describe.
I'm unclear what the best way currently is to make use of type annotations in my own aiohttp projects.

💡 Describe the solution you'd like
One of the aiohttp-demos to be updated with full type hinting to serve as an example.

❓ Describe alternatives you've considered
The only way I can see at the moment, is with importing protected objects from various modules.

e.g. from aiohttp.web_app import _Handler
though this is also in aiohttp.web_urldispatcher._WebHandler

Types to add:

• Handler
• Middleware
• CleanupContext (Cleanup Context type alias #5883 (comment))

[hyzyla]

You can define all types in your code using public classes:

from aiohttp import web

Handler = Callable[[web.Request], Awaitable[web.StreamResponse]]

But, I think, that defining a common combination of types will improve the user experience of working with a library

[Dreamsorcerer]

That is also possible, but seems even less maintainable than importing protected variables.

Hardcoded types in my code is more difficult to ensure they are correct and that they get updated if the signatures change in future.

[playpauseandstop]

Can add +1 here.

In my aiohttp libraries, such as aiohttp-middlewares I’m importing _Handler and _Middleware from aiohttp.web_middlewares and redefine it to Handler & Middleware for later reuse across the library.

While, in reality I would like to have ability to import aiohttp type annotations such as,

from aiohttp.web_typing import Handler, Middleware  # and so on

Or from aiohttp.annotations module, or from aiohttp.typing module, doesn’t matter. Main point to have single entry point with all reusable type annotations to use in other aiohttp libraries and projects.

ps. As implementation reference there is a pyrsistent.typing module, which provides type annotations for pyrsistent library in very clear way for 3rd party users
pps. I found out, that there is aiohttp.typedefs module already, but from quick overview it missed many usable type annotations, such as Handler, Middleware

[Dreamsorcerer]

We've added the Handler type now.
Sounds like we should also add a Middleware type. Is there anything else that people think are missing?