Aiohttp: Unclosed client session warning

[tahajahangir]

Long story short

We see rare logs with error level ERROR saying Unclosed client session during normal operation.

Expected behaviour

No log!

Actual behaviour

Sample log:

2016-09-14 18:42:28,511 ERROR asyncio Unclosed client session
client_session: <aiohttp.client.ClientSession object at 0x7fd2b06469b0>

As an aiohttp user, can we do anythin to prevent unclosed sessions? If no, it's better to have a specific warning class (subclass of ResourceWarning), not just using the original base class.

Steps to reproduce

Cannot reproduce manually!

Your environment

Debian 8
Python 3.5.2
aiohttp (0.22.5)

[asvetlov]

Either use async with aiohttp.ClientSession() as session: ... or call await session.close() explicitly.

[tahajahangir]

We don't use ClientSession directly:

async with aiohttp.post(check_url, data=data) as resp:
    if resp.status == 200:
        return await resp.json()

Is it wrong?!

[asvetlov]

It's deprecated and removed from the documentation's _usage_ part.
Perhaps we had reasons for it, isn't it?
And the main reason is impossibility to provide steady graceful shutdown with this API.

[Kentzo]

@asvetlov Unfortunately warnings.warn is not a widely adopted (or known?) technique. And even fewer users know in advance that particular package utilizes it.

Maybe a banner should be added to the tutorial stating that? Or even a suggestion to turn warnings into exceptions?

[asvetlov]

Teaching users to working with warnings is out of scope of this project.
I don't want to mess tutorials with banners like notes or warnings.
Even Django (super newbie friendly tool) just uses DeprecationWarning.

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