python3 Django2.0 环境下，如果你遇到namespace没有注册以及在根目录下urls.py中的include方法的第二个参数namespace添加之后就出错的问题。请在[app_name]目录下的urls.py中的urlpatterns前面加上app_name=’app_name’， app_name代表你的应用的名称。可以参考这篇：https://stackoverflow.com/questions/14892462/django-error-upolls-is-not-a-registered-namespace
Specifying a namespace in include() without providing an app_name ‘
django.core.exceptions.ImproperlyConfigured: Specifying a namespace in include() without providing an app_name is not supported. Set the app_name attribute in the included module, or pass a 2-tuple containing the list of patterns and app_name instead.