Flask app: logging inside a (non-flask-related) class fails

I have a flask app that I wanted to add a cache to for API calls, so I wrote a simple caching class that doesn't know anything about flask, just about the cache data, and managing it. It lives in a separate file that starts:

import logging
import time

logger = logging.getLogger(__name__)


class CacheCollection:

and uses logger.debug("xxx") in various places to let you know what's going on.

That all works fine in standalone test code.

HOWEVER, I would like to create this cache in my flask app, and ideally seed it with data when the application starts up. Since Flask hasn't got a "on startup" event like Django does, I am adding this in the init_bp() method of my Blueprint. It needs to be after Flask's config is loaded, since the endpoint and key for the API I'm caching is in that config.

When I do that, I get a warning on the first call to the logger in the cache class:

RuntimeError: Working outside of application context.

which is true I guess, but I don't see why it's relevant. Does Flask mess with the logging config enough to break other modules' logging? Having to create a dependency on current_app.logger in this other module seems perverse (and I don't think it will help).

How should I be creating these objects outside of a request? I don't want to use before_first_request, since it might take a while to run. Other similar questions on SO seem to be for work unrelated to the application itself, running in another thread or something similar.

from Flask app: logging inside a (non-flask-related) class fails