## app1/constants.py

MY_VAR = 100

## app1/settings.py

from django.conf import settings
from app1 import constants

MY_VAR = getattr(settings, 'MY_VAR', constants.MY_VAR)

## app1/views.py

from django.conf import settings
from app1 import settings as app1_settings

print app1_settings.MY_VAR

## project/settings/__init__.py

# MY_VAR = 200