Example of loosely coupling Django apps using settings.

models.py

from django.db import models

# Import the PROJECT_MODEL string from the current app's settings
from .settings import PROJECT_MODEL


class Task(models.Model):
    """
    Instead of explicitly giving the model for the FK as a Python object or
    explicitly stating a string in the form '<app>.<modelname>', we'll use
    the imported setting.
    
    In really ridiculous occasions we could even make this one conditional::
    
        if PROJECT_MODEL:
            project = models.ForeignKey(PROJECT_MODEL)
    
    (Yes, this works.)
    """
    # Instead of explicitly stating the string 
    project = models.ForeignKey(PROJECT_MODEL)

settings.py

from django.conf import settings

"""
Using 'federated' settings really helps keeping oversight of
the settings for a particular Django app. This way we allways
know *where* settings are, *what* they are named and what their
*defaults* are.

In a typical use case you would document every single setting
with a piece of comment.

In the Django `settings.py`, this would look like this::

    # Use Swiss cheese instead of projects.Project for linking tasks to.
    <APP_NAME>_PROJECT_MODEL = 'cheese.Swisscheese'
"""

# The project model, allowing a generic way to link tasks to whatever it
# is they relate to - and allow full flexibility on how Projects will be
# implemented.
#
# The default is to use the Project model from the projects app.
PROJECT_MODEL = getattr(settings, '<APP_NAME>_PROJECT_MODEL', 'projects.Project')