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.
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.
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
django.conf.settings is a normally a proxy around your
settings.py file, but not always.
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).
So there are a few great reasons to use
from django.conf import settings instead of importing the
- 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.