django/conf/__init__.py/class_Settings

摘自如题文件内容，如有侵权，请联系 QQ 929054468 删除
class Settings:
    def __init__(self, settings_module):
        # update this dict from global settings (but only for ALL_CAPS settings)
        for setting in dir(global_settings):
            if setting.isupper():
                setattr(self, setting, getattr(global_settings, setting))

将本地模块 global_settings 中的属性值导入到实例对象中

        # store the settings module in case someone later cares
        self.SETTINGS_MODULE = settings_module

        mod = importlib.import_module(self.SETTINGS_MODULE)

利用 importlib模块导入新增的模块  SETTINGS_MODULE

        tuple_settings = (
            "INSTALLED_APPS",
            "TEMPLATE_DIRS",
            "LOCALE_PATHS",
        )
        self._explicit_settings = set()
        for setting in dir(mod):
            if setting.isupper():
                setting_value = getattr(mod, setting)

                if (setting in tuple_settings and
                        not isinstance(setting_value, (list, tuple))):
                    raise ImproperlyConfigured("The %s setting must be a list or a tuple. " % setting)
                setattr(self, setting, setting_value)
                self._explicit_settings.add(setting)

将新增的模块属性值导入到实例对象中

        if not self.SECRET_KEY:
            raise ImproperlyConfigured("The SECRET_KEY setting must not be empty.")

检测新导入的属性值中有没有 SECRET_KEY 属性值，且不为空

        if self.is_overridden('DEFAULT_CONTENT_TYPE'):
            warnings.warn('The DEFAULT_CONTENT_TYPE setting is deprecated.', RemovedInDjango30Warning)

检查属性名 DEFAULT_CONTENT_TYPE 是否在新导入的模块属性中，否则进行warn提醒

        if hasattr(time, 'tzset') and self.TIME_ZONE:
            # When we can, attempt to validate the timezone. If we can't find
            # this file, no check happens and it's harmless.
            zoneinfo_root = '/usr/share/zoneinfo'
            if (os.path.exists(zoneinfo_root) and not
                    os.path.exists(os.path.join(zoneinfo_root, *(self.TIME_ZONE.split('/'))))):
                raise ValueError("Incorrect timezone setting: %s" % self.TIME_ZONE)
            # Move the time zone info into os.environ. See ticket #2315 for why
            # we don't do this unconditionally (breaks Windows).
            os.environ['TZ'] = self.TIME_ZONE
            time.tzset()

设置时区，首先会检查 time 模块是否有 tzset 方法，和对象导入的模块是否有TIME_ZONE属性，根据TIME_ZONE在linux服务器的 /usr/share/zoneinfo 查找对应的时区，如果对应的时区文件不存在，则抛出异常，
然后重新设置时区

    def is_overridden(self, setting):
        return setting in self._explicit_settings

    def __repr__(self):
        return '<%(cls)s "%(settings_module)s">' % {
            'cls': self.__class__.__name__,
            'settings_module': self.SETTINGS_MODULE,
        }