django "not a registered namespace" code example

Example 1: app is not a registered namespace django

# From: https://stackoverflow.com/a/41883421/3673842
path('', include(('app_name.urls', 'app_name'), namespace='app_name'))

# E.g. path('', include(('home.urls', 'home'), namespace='home'))

Example 2: 'djdt' is not a registered namespace

if settings.DEBUG:
    import debug_toolbar

    urlpatterns += [
        url(r'^__debug__/', include(debug_toolbar.urls)),
    ]