python引入类报错 Apps aren't loaded yet

from blog.models import Book.Author报错如下:

django.core.exceptions.ImproperlyConfigured: Requested setting DEFAULT_INDEX_TABLESPACE, but settings are not configured. You must either define the environment variable DJANGO_SETTING
S_MODULE or call settings.configure() before accessing settings.

django.core.exceptions.AppRegistryNotReady: Apps aren't loaded yet

解决办法:

>>> import os;
>>> os.environ['DJANGO_SETTINGS_MODULE'] = 'mtm.settings';
>>> import django;
>>> django.setup();
>>> from blog.models import Book,Author

引自： http://www.dark-hamster.com/programming/how-to-resolve-error-message-django-core-exceptions-appregistrynotready-apps-arent-loaded-yet/