Slow to import

[Dreamsorcerer]

On my system, import aiohttp_debugtoolbar takes ~1.6s to run.

This seems excessive, and adds a noticeable amount of time to app reloading when developing with aiohttp-devtools.

[asvetlov]

I'm curious, why?
Did you try python -X importtime ... to analyze?

[Dreamsorcerer]

Not sure how to read importtime output, but viewing through tuna looks like this:

If I'm reading that correctly, it looks like most of the time is probably spent with this packages code:
https://github.com/aio-libs/aiohttp-debugtoolbar/blob/master/aiohttp_debugtoolbar/panels/versions.py#L12-L33

A secondary issue is gunicorn getting imported via aiohttp.workers. Maybe it would be best to remove the gunicorn workers from aiohttp/__init__.py in v4? Just require users to import the workers directly if needed (same for anything else that's having a noticeable impact on the import time).

[asvetlov]

The main issue is pkg_resources, the famously slow package :)
I suggest replacing it with importlib.metadata.

Regarding gunicorn import -- yes. After upgrading the minimal required Python to 3.7 we can do __getattr__ trick, similar to concurrent.futures.

If you can find time for both improvements -- you are welcome!