import os
import sys

from mysite.settings import settings

if __name__ == '__main__':
    os.environ.setdefault('DJANGO_SETTINGS_MODULE', settings.ACTIVE_SETTINGS)

import datetime
import os
ACTIVE_SETTINGS = 'mysite.settings.dev_settings'

more default settings.....

from django.conf import settings

from mysite.settings import settings as default
# use this could set default settings to active setting
settings.configure(default, DEBUG=True)

more dev settings.....