Remove on_startup, on_shutdown, event system and deprecated lifespans

[adriangb]

#2067

Close to 500 LOC removed. That's ~ 1/20th of the codebase.

[euri10]

what do you think about adding a little "migration" guide like:

you used to do this:

async def startup():
	await open_some_ressource()
async def shutdown():
	await close_some_ressource()
app = Starlette(
	routes=routes,
	on_startup=[startup],
	on_shutdown=[shutdown]
)

now do this:

@asynccontextmanager
async def lifespan():
	try:
		await open_some_ressource()
		yield
	finally:
		await close_some_ressource()
app = Starlette(
    routes=routes,
	lifespan=lifespan
)

or it's too obvious ?

[adriangb]

I don't think it's too obvious, I agree we should add it. But we should probably do the same for all of the things we are deprecating / removing. Maybe it's time to start a v1migration.md doc that I can add to in this PR?

[euri10]

shouldn't those 2 lines be interverted ?

[euri10]

you mean uvicorn right ?

[euri10]

seems to me that this becomes outdated since there wont be startup and shutdown handlers

[gnat]

So, what do we do now? This is a breaking change.

@asynccontextmanager
async def lifespan():
	try:
		await open_some_ressource()
		yield
	finally:
		await close_some_ressource()
app = Starlette(
    routes=routes,
	lifespan=lifespan
)

This is really not obvious.

Is there any way to get the equivalent functionality of on_startup, on_shutdown more intuitively?

The DX of being able to just specify a function for these important events is a good thing.

[gnat]

Side "meta" note, what is with all the breaking PR's this year? Is the plan to force everyone to completely re-learn Starlette and re-write their apps for 1.0... 🤷 What makes this more egregious is the proposed patterns have worse DX

@tomchristie

[adriangb]

Your example is very contrived, I seriously doubt anyone is doing that.

[gnat]

Not my code, re: #2068 (comment)

[adriangb]

Misread. Thought you were yielding a something, which, indeed, would be breaking, but like I said very contrived.

We have documentation for this. And there are good reasons why this approach is much better than two separate functions. I’m afraid I do not agree that it is very non-obvious how to use.

[gnat]

We have documentation for this.

Is this what you're referring to?

• https://github.com/encode/starlette/pull/2068/files#diff-2cee6a30a4169080ec68af68d0a8555732955725fe34fbca732dd06e3e55a4a5
• https://fastapi.tiangolo.com/advanced/events/#lifespan

[gnat]

asyccontextmanager should be asynccontextmanager

[gnat]

asyccontextmanager should be asynccontextmanager

[adriangb]

https://www.starlette.io/lifespan/

[Kludex]

Decisions can be reversed until 1.0... But a better place to talk about it would be the discussion that was taken. I'm on my phone right now.

[Kludex]

The idea of deprecating things now is to avoid doing so on 1.0.

Feedback is always welcome, and if we made a mistake, we can revert decisions.

[gnat]

For people reading this PR, FastAPI went official with this in 0.93.0, only a few days ago: #2067 (comment)

Totally fair with the discussion that happened in: #2067 That's fine. The cat is out of the bag at this point.

Gonna go make the changes to my Starlette apps now.

[Kludex]

Cool.

But in any case, we are always open to take decisions back if they make sense. We don't want to harm users, and I think we try to always be transparent here.

[dineshbvadhia]

@Kludex
As of today, the FastApi/Starlette lifespan feature results in an "async generators are unimplemented" error when compiling with mypyc. Until mypyc supports async generators, the on_startup/on_shutdown feature should be retained as it passes with mypyc.

[Kludex]

@Kludex As of today, the FastApi/Starlette lifespan feature results in an "async generators are unimplemented" error when compiling with mypyc. Until mypyc supports async generators, the on_startup/on_shutdown feature should be retained as it passes with mypyc.

Ref.: mypyc/mypyc#868

[Kludex]

I've applied this on #2384, and given co-author to @adriangb there. FYI

[graingert]

@Kludex As of today, the FastApi/Starlette lifespan feature results in an "async generators are unimplemented" error when compiling with mypyc. Until mypyc supports async generators, the on_startup/on_shutdown feature should be retained as it passes with mypyc.

You don't need to use async generators to create an async context manager you can just manually implement __aenter__ and __aexit__ on a class