Defining overwritable app settings

This recipe will show you how to define settings for your app that can be then overwritten in your project's settings.py file. This is useful especially for reusable apps.

Getting ready

Follow the steps for Getting ready in the Creating app configuration recipe to create your Django app.

How to do it...

1. If you just have one or two settings, you can use the following pattern in your models.py file. If the settings are extensive and you want to have them organized better, create an app_settings.py file in the app and put the settings in the following way:

# magazine/models.py or magazine/app_settings.py
from django.conf import settings
from django.utils.translation import ugettext_lazy as _
 
SETTING1 = getattr(settings, "MAGAZINE_SETTING1", "default value")
MEANING_OF_LIFE = getattr(settings, "MAGAZINE_MEANING_OF_LIFE", 42)
STATUS_CHOICES = getattr(settings, "MAGAZINE_STATUS_CHOICES", (
    ("draft", _("Draft")),
    ("published", _("Published")),
    ("not_listed", _("Not Listed")),
))

2. If the settings were defined in an app_settings.py file, then you can import and use them in models.py, as follows:

# magazine/models.py
from django.db import models
from django.utils.translation import ugettext_lazy as _

from .app_settings import STATUS_CHOICES


class NewsArticle(models.Model):
    # ...
    status = models.CharField(_("Status"),
                              max_length=20,
                              choices=STATUS_CHOICES)

3. If you want to overwrite the STATUS_CHOICES setting for a given project, you simply open settings.py for that project and add the following:

# settings.py
from django.utils.translation import ugettext_lazy as _

# ...

MAGAZINE_STATUS_CHOICES = (
    ("imported", _("Imported")),
    ("draft", _("Draft")),
    ("published", _("Published")),
    ("not_listed", _("Not Listed")),
    ("expired", _("Expired")),
)

How it works...

The getattr(object, attribute_name[, default_value]) Python function tries to get the attribute_name attribute from object and returns default_value if it is not found. In this case, different settings are tried in order to be taken from the Django project settings.py module or, if they are not found, the default values are assigned.