from django.conf import settings  # 入口

settings = LazySettings()  # 单例



from django.conf import global_settings

class LazySettings(LazyObject):

　　def _setup(self, name=None):

　　　　settings_module = os.environ.get(ENVIRONMENT_VARIABLE)  # 获取全局的键值对,在manage.py中启动时就已经设置了一个

       self._wrapped = Settings(settings_module)

class Settings(object):

　　def __init__(self, settings_module):

　　　　for setting in dir(global_settings):  # 先获取系统默认配置里面的所有的变量名

　　　　　　if setting.isupper():

                setattr(self, setting, getattr(global_settings, setting))  # 给settings对象设置键值对

                self.SETTINGS_MODULE = settings_module

                mod = importlib.import_module(self.SETTINGS_MODULE)

       for setting in dir(mod):

       　　if setting.isupper():

          setting_value = getattr(mod, setting)

          setattr(self, setting, setting_value)  # 给settings对象设置键值对