From Django docs:
You shouldn’t alter settings in your applications at runtime. Forexample, don’t do this in a view:
from django.conf import settingssettings.DEBUG = True # Don't do this!The only place you should assign to settings is in a settings file.
I've noticed that Django testing code does alter settings. Why is it ok to do it there?
Short answer: No, unless you do it during the startup.
Long answer:
Django docs are correct, you should not modify settings at runtime. This means, no settings modifications after the app has been started, like changing configuration in views.py, serializers.py, models.py or other modules you add during the development. But it is ok to modify settings if they depend on local variables if you do it at startup and you are fully aware of what happens.
Yes, if you think you need it. Feel free to rely on override_settings to change settings value for testing purposes in the unit tests, see example of usage here
Also, everything that this decorator does - is overriding settings with provided values and restoring settings value after test has passed (decorated function executed).
From what I see, they change settings only for testing purposes and the only thing they do - adding a local host to allowed host so they can test the code using a local domain. Examples like that seem pretty reasonable for me as change is done only once and during unit tests set up. Imagine having overrride_settings call every time, that would be monstrous.
Try not to, there is no need to modify settings and if there is - think about it, maybe settings is not the right place for a mutable setting? If you want to modify settings at runtime - please be aware that settings might be cached somewhere, copied and accessed all over the place - this is a plenty of space for new bugs. There is nothing bad in it, except having an unexpected behavior of the system due to an old/new value of the modified setting.
Hope this makes sense.