Django " environment variable DJANGO_SETTINGS_MODULE is undefined"问题的解决

在学习 《The difinitive guide to Django 2nd》models这章的时候，为mysite创建了一个app books，books中models已经创建了对应数据库的model，这个时候想用python shell环境来测试，但是输入

from books.models import Publisher

的时候，报如下错误“Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "books\models.py", line 1, in <module>
    from django.db import models
  File "C:\Python25\Lib\site-packages\django\db\__init__.py", line 11, in <modul
e>
    if DEFAULT_DB_ALIAS not in settings.DATABASES:
  File "C:\Python25\Lib\site-packages\django\utils\functional.py", line 184, in
inner
    self._setup()
  File "C:\Python25\Lib\site-packages\django\conf\__init__.py", line 40, in _set
up
    raise ImportError("Settings cannot be imported, because environment variable
%s is undefined." % ENVIRONMENT_VARIABLE)
ImportError: Settings cannot be imported, because environment variable DJANGO_SE
TTINGS_MODULE is undefined.”
最重要的是最后一句，because environment variable DJANGO_SE
TTINGS_MODULE is undefined.

DJANGO_SE
TTINGS_MODULE 并未定义。
解决方法：在mysite目录下，用python manage.py shell启动python解释器环境，然后在from.. import ...成功。