[Django]-ImproperlyConfiguredError about app_name when using namespace in include()

Django 1.11+, 2.0+

You should set the app_name in the urls file you are including

# reviews/urls.py  <-- i.e. in your app's urls.py

app_name = 'reviews'
     

Then you can include it the way you are doing it.

Also, it might be worth noting what Django docs say here https://docs.djangoproject.com/en/1.11/ref/urls/#include :

Deprecated since version 1.9: Support for the app_name argument is
deprecated and will be removed in Django 2.0. Specify the app_name as
explained in URL namespaces and included URLconfs instead.

( https://docs.djangoproject.com/en/1.11/topics/http/urls/#namespaces-and-include )

Django 2.0 you should specify app_name in your urls.py, is not necessary to specify app_name argument on include.

Main Url file.

from django.contrib import admin
from django.urls import path, include

urlpatterns = [
    path('', include('apps.main.urls')),
    path('admin/', admin.site.urls),
]

Included Url.

from django.urls import path
from . import views

app_name = 'main_app'

urlpatterns = [
    path('', views.index, name='index'),
]

Then use use in template as

<a href="{% url main_app:index' %}"> link </a>

More details: https://code.djangoproject.com/ticket/28691
Django 2.0 Docs

I included a library not (fully) django 2.1 compatible yet (django_auth_pro_saml2). Hence I create a second file saml_urls.py:

from django_saml2_pro_auth.urls import urlpatterns

app_name = 'saml'

Such that I could include the urls as:

from django.urls import include, re_path as url

urlpatterns = [
    ..., url(r'', include('your_app.saml_urls', namespace='saml')), ...
]

Hacky, but it worked for me, whereas the url(r'^reviews/', include(('reviews.urls', 'reviews'), namespace='reviews')) did not.

I am also face the same error in Django 2.2 and i solve it this way

urls.py file

urlpatterns = [
   path('publisher-polls/', include('polls.urls', namespace='publisher-polls')),
]

polls/urls.py file

app_name = 'polls'
urlpatterns = [
  path('', views.IndexView.as_view(), name='index')
]

example use of namespace in calss based view method

def get_absolute_url(self):
    from django.urls import reverse
    return reverse('polls.index', args=[str(self.id)])

example use of namespace in templates

{% url 'polls:index' %}

Here polls:index mean app_name[define in polls/urls.py file]:name[define in polls/urls.py file inside path function]

their official which is pretty good you can check for more info namespace_django_official_doc

Find unused files or directories in APP (reviews) directory, and detete this items !

In project level urls.py

path('',include('appname.urls'), namespace= 'test')

Now in in your app level urls.py

app_name = 'test'
path('',views.index, name= 'home')

Long story short is, You have to provide "app_name" in your app level urls and that same name should be your namespace name at project level url