set_loop for app check, allow app_factory()

[samuelcolvin]

fixes #88.

[asvetlov]

Would you accept coroutine as app_factory?

[samuelcolvin]

Easy enough to do.

I'm not sure how that would work when running the code in production. Eg. Gunicorn doesn't accept a coroutine, and if you're using web.run_app(), you'd have to do something ugly with loop.run_until_complete.

Why would a coroutine be useful? surely anything requiring a running loop can be done in startup coroutines?

Perhaps having app_factory as a coroutine could encourage people to setup their app in a way which will be hard to deploy?

Very happy to add the functionality if it's useful.

[codecov]

Codecov Report

Merging #96 into master will increase coverage by 0.03%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master     #96      +/-   ##
=========================================
+ Coverage   95.06%   95.1%   +0.03%     
=========================================
  Files          12      12              
  Lines         770     776       +6     
  Branches       92      92              
=========================================
+ Hits          732     738       +6     
  Misses         26      26              
  Partials       12      12

Impacted Files	Coverage Δ
aiohttp_devtools/cli.py	100% <ø> (ø)	⬆️
aiohttp_devtools/runserver/serve.py	93.27% <100%> (-0.06%)	⬇️
aiohttp_devtools/runserver/config.py	88.28% <100%> (+0.78%)	⬆️
aiohttp_devtools/version.py	100% <100%> (ø)	⬆️

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[asvetlov]

Well, let's discuss.
My main motivation is creating every async object (the object that should cooperate with asyncio loop) inside a coroutine.
It allows to skip explicit event loop passing but get implicit running loop used for coro execution.
Maybe we end up with something like run_forever() from python/asyncio#465
I still don't know how to better integrate this approach with gunicorn.
We could add support for coroutine factory to aiohttp.worker easy though.
And after that got smoothly to dropping ._init_loop() trick at all.

[samuelcolvin]

Let's leave the coroutine question for now. Happy to add it later if it's needed.