Django Doctor audits code and auto fixes Django anti-patterns. We checked 666 Django projects for problems hindering maintainability and found that 5% of the Django websites don't use django.conf.settings read more.
We also manually checked a sample of the affected lines in the public repos, and were shocked that this was not "beginners making mistakes" - most were in mature large projects. That makes sense: the longer a codebase lives the greater the scope for tech debt to creep in, and the more lines of code the easier it is for the bad to hide in plain sight. Indeed I suspect, like most people, you don't read every single import when you open a python file. It's easy to miss this tech debt.
How would you solve maintainability problems? Try our Django refactor challenge.
Naked settings, if you will
Django best practice tells us importing settings.py is bad and we should instead use from django.conf import settings, hence Django Doctor gives this advice when reviewing GitHub PRs:
But whey does Django best practice say avoid naked settings and instead use django.conf.settings? A simple answer is naked settings.py will not have the Django default values and can trigger a race condition, but there is more to it than that.
Overriding settings in tests is simplified too when using django.conf.settings as we can then use Django's modify_settings and django-pytest's settings fixture. This helps avoid unmaintainable flaky tests as one test's changes cannot affect another because changes are reset after the test finishes.
To understand how that works we need to look deeper at what django.conf.settings is exactly.
Proxy for a swappable sources of truth
django.conf.settings is not a module. It's an instance of LazySettings. This object is a wrapper around a "holder" of the actual settings. During the normal running of your Django app, that holder ingests the values in the file defined by the environment variable DJANGO_SETTINGS_MODULE, which you will recognize from manage.py, or if you ever tried importing Django from the python shell without first setting that variable and getting the classic
django.core.exceptions.ImproperlyConfigured: Requested setting
INSTALLED_APPS, but settings are not configured. You must either
define the environment variable DJANGO_SETTINGS_MODULE
or call settings.configure() before accessing settings.
As the name "lazy" implies, the values from DJANGO_SETTINGS_MODULE are not evaluated until they are interacted with. This is how we can import settings throughout our codebase with confidence that we will not get an error that the app is not ready yet.
So we can see, django.conf.settings is not the same thing as the settings.py file: django.conf.settings is a normally a proxy around your settings.py file, but not always.
UserSettingsHolder
During tests it's convenient to use very different values to those in your settings.py, or maybe the project does not have a settings.py (such as a third-party library).
For these cases we can explicitly call settings.cofigure(). When that happens the django.conf.settings's holder will be a UserSettingsHolder, and not interact with settings.py at all.
So there are a few great reasons to use from django.conf import settings instead of importing the settings.py directly:
- You get Django's default values set
- It simplifies safely overriding settings during tests
- It avoid triggering app is not ready exceptions
Beware though that lowercase values in your settings.py are not exposed to django.conf.settings, but you can store those values in some other files so not a huge loss.
Does your codebase import settings.py directly?
Over time it's easy for tech debt to slip into your codebase. I can check that for you at django.doctor, or can review your GitHub PRs:
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