settings.py

# Most normal settings

DEFAULT_FILE_STORAGE = 'django.core.files.storage.FileSystemStorage'
STATICFILES_STORAGE = 'django.contrib.staticfiles.storage.StaticFilesStorage'

try:
    execfile(os.path.join("/etc/project", "settings_local.py"))
except IOError:
    execfile(os.path.join(SITE_ROOT, 'settings_local.py'))

settings_local.dev.py

SITE_ID=1

DATABASE = {
.....
}

settings_local.production.py

SITE_ID=3

DATABASE = {
.....
}

settings_local.staging.py

SITE_ID=2

DATABASE = {
.....
}

And in production, we copy settings_local.production.py to /etc/project, In staging, settings_loca.staging.py to /etc/project, and so on.