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How to use namespace in django + Problems after this

I looked at the official Django documentation(https://docs.djangoproject.com/en/3.2/topics/http/urls/#reversing-namespaced-urls) and the error code and wrote the following. How can I write namespaces to work?
views.py:
from django.urls import path, include
app_name = 'home'
urlpatterns = [
path('math/', include('math_note.urls', namespace='math-note'))
]
templates:
math note
Error when running runserver:
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.
Question:
How can I use the namespace function?
Second question:
Thank you! Well connected via
<a href="{% url 'music:home-page' %}">(to app_name = music)
But when I call the form from the music app and load the url to generate, I get an error. The other URLs didn't have any issues, only this one.
Reverse for 'home-page' not found. 'home-page' is not a valid view function or pattern name.
#music/urls.py
from django.urls import path
from . import views
app_name = 'music'
urlpatterns = [
path('', views.music_home_page, name='home-page'),
path('new/', views.new_song, name='new'),
path('music_player/<int:id>/', views.music_player, name='music-player'),
]
Question:
I solved the previous problem and got the following problem. What is the cause and solution of this?

The namespace kwarg that include accepts is an instance namespace i.e. an instance of an application namespace, you cannot have instance namespaces without having an application namespace which as the error specifies you do by specifying app_name in the included module or by passing a 2-tuple containing the patterns and application namespace to include.
Hence you need to modify math_note.urls and add an app_name variable to it:
app_name = 'math_note'
urlpatterns = [
...
]
Keep your other urls (likely in home.urls?) as it is:
from django.urls import path, include
app_name = 'home'
urlpatterns = [
path('math/', include('math_note.urls', namespace='math-note'))
]

just remove namespace from the path.
including a url does not require to have namespace. having your namespace on your math-notes is enough.

views.py
from django.urls import path, include
app_name = 'home'
urlpatterns = [
path('math/', include('math_note.urls', name='math-note'))
]
Use name instead of namespace

app_name in application url will work as namespace. just remove namespace from include in root project directory.
your urlpatterns should look like:
urlpatterns = [
path('math/', include('math_note.urls'))
]
and define app_name='home' in your application urls.
something like:
`app_name='home'`
urlpatterns = [
path('list/', <your view>, name='app-list'),
]

second question answer.
I have set the navbar so I can't see the exact error code content. When I deleted the navbar, I saw the exact error content, and the cause of the error was the return link.

Django Reverse the mapper, URL name doesn't work

I'm currently doing on Django project and using reversing the mapper on urls.py. Before I use reversing it worked well, but after I change it to reversing, it started to do not work anymore.
I want to know why it doesn't work. Is it because I didn't add it in proejct file's urls.py? How can I call that url with the name in app's file?
from django.urls import path
from . import views
app_name = 'posting'
urlpatterns = [
path('', views.index, name='index'),
path('<int:post_id>', views.post, name='post'),
path('posting', views.posting, name='postingform')
]
index.html
<a href='{% url 'postingform' %}'>Upload your beer now!</a>

Since you defined an app_name in your urls.py, yo need to specify the name of the view with the app_name:
<a href='{% url 'posting:postingform' %}'>Upload your beer now!</a>

What is difference between instance namespace and application namespace in django urls?

I am referring https://www.webforefront.com/django/namedjangourls.html to understand django urlconfs. I have encountered terms instance namespace and application namespace. I know about namespaces in urlsconfs. But I don't know the difference between them.
I referred django docs for it. It mentions that instance and app namespaces, comes into picture, when multiple instances of same app is used in django project.
But still, I am not able to understand it. I have googled out, but couldn't find any help on it.
Thanks in advance.

Think of instance namespace as your nickname and application namespace as your real name.
People can have many nicknames for you, but your real name doesn't change.
Django uses the application namespace (your real name) to reverse urls, cause as an application you should not care how many instance namespaces (nicknames) there are.
But to differentiate between one instance and the next, you will use the instance namespaces (nicknames) in urlconfs.
Let's say your app deals with customers and store employees. Both of these have physical addresses and you might want to use an app that just handles all address information: forms, validation, model structure, geo location etc. Our fictional app is a reusable django app called "django_super_address".
Your root url conf may look like this:
urlpatterns = [
path('customer/address/',
include('django_super_address.urls',
namespace='customer_address')
),
path('employee/address/',
include('django_super_address.urls',
namespace='employee_address')
),
]
This includes the same urls below different URL paths, pointing to the same app, using different namespaces (nicknames).
Within django_super_address, it has defined it's application namespace:
# File: django_super_address/urls.py
from . import views
app_name = 'django_super_address'
urlpatterns = [
path('create/', views.SomeAddressCreateView.as_view(),
name='address_create'),
path('create/success/', views.SuccessView(),
name='address_create_success'),
...
]
And in views it uses:
# File django_super_address/views.py
class SomeAddressCreateView(generic.CreateView):
def success_url(self):
return reverse(
'django_super_address:address_create_success'
)
...
When Django gets the URL `/employee/address/create/':
It sets the instance namespace to employee_address
It reads the urls from django_super_address
It sets the application namespace to django_super_address and
associates the urls.py with that application namespace.
In the view:
It reverses the URL by looking at the urls file associated with the application namespace (real name) and reverses the name into: create/success
It then goes back up the chain, now using the instance namespace (nickname) to prepend the rest of the url: root + employee/address/ + create/success/ = /employee/address/create/success/
And there you have it: nicknames for urlconfs and application namespaces for reverse!

From my understanding, it goes like this:
For two different applications using the same URL pattern, use an Application namespace.
For two different instances of the same application using the same URL configuration and views, use an Instance namespace.
The application of Instance namespace might sound a bit confusing. Let me try to clarify if that's the case. Consider the example given in the Django docs.
urls.py:
from django.urls import include, path
urlpatterns = [
path('author-polls/', include('polls.urls', namespace='author-polls')),
path('publisher-polls/', include('polls.urls', namespace='publisher-polls')),
]
polls/urls.py:
from django.urls import path
from . import views
app_name = 'polls'
urlpatterns = [
path('', views.IndexView.as_view(), name='index'),
path('<int:pk>/', views.DetailView.as_view(), name='detail'),
...
]
The namespaces are defined like this:
The Application namespace is defined by app_name attribute in polls/urls.py
The Instance namespace is defined by namespace argument in urls.py
Here, both author-polls and publisher-polls are using the same polls.urls to resolve their URLs. Without an Instance namespace, resolving a URL like 'polls:index' could create confusion on which URL it's intending to fetch. That's why Django has a set of protocol defined to fix this issue for all kinds of situations when you are attempting to reverse and resolve namespaced URLs.

You can use the urls.py for an app by including it in different urls path, for example we can have:
urlpatterns = [
path('author-polls/', include('polls.urls')),
path('publisher-polls/', include('polls.urls')),
]
As you see, both included polls.urls which is:
app_name = 'polls' urlpatterns = [
path('', views.IndexView.as_view(), name='index'),
path('<int:pk>/', views.DetailView.as_view(), name='detail'),
...
]
So far so good!
But there is a problem. In the template, where is 'polls:index' pointing?!
And now instance namespace comes into the picture.
urlpatterns = [
path('author-polls/', include('polls.urls', namespace='author-polls')),
path('publisher-polls/', include('polls.urls', namespace='publisher-polls')),
]
Django has some rules to reverse namespace urls >> https://docs.djangoproject.com/en/3.0/topics/http/urls/#reversing-namespaced-urls

basically each application namespace can have multiple instance namespace ,
for example :
this is project URLs file (main urls) :
path('', include("movie_app.urls")),
path('my_namespace1/', include("movie_app.urls", namespace='my_namespace1')),
path('my_namespace2/', include("movie_app.urls", namespace='my_namespace2')),
you can see, they all mentions to the same app.urls file (movie_app.urls) , but the path link are different .
first one is : "",
and second one is : "my_namespace1/",
and the third is : "my_namespace2/",
and this is movie_app.urls file (child file ) :
app_name = 'movie_app'
urlpatterns = [
path('appmovie1/', myview1 , name="myname"),
]
now when you use the all paths in your html templates for example :
<h1> application namespace : url name</h1>
<h1>instance namespace1 : url name</h1>
<h1>instance namespace2 : url name </h1>
you will note the different in href link :
<h1> application namespace : url name</h1>
<h1>instance namespace1 : url name</h1>
<h1>instance namespace2 : url name </h1>
in the end:
app namespace and instance name space will help you to determine / select the correct URL path from multiple URL paths that use same include .urls file.
I hope this helpful for you .

The namespace instance can only be used with include. This is useful when we want to have multiple paths with different URLs, but we want to include the same URLconf modules.
Let's say we have this code:
#my_site/urls.py
urlpatterns = [
path('url1/',include('english.urls')),
path('url2/',include('english.urls'))]
#english/urls.py
app_name='english'
urlpatterns = [
path('words/', views.index, name='words')]
#template.html
Something
Clicking on the link will redirect us to url1/words, because Django will choose the first element from the urlpatterns. If we want to be redirected to url2/words, we must use the namespace (instance namespace), that is:
#my_site/urls.py
urlpatterns = [
path('url1/',include('english.urls', namespace='eng')),
path('url2/',include('english.urls', namespace='eng2'))]
#english/urls.py
app_name='english'
urlpatterns = [
path('words/', views.index, name='words')]
and then:
#template.html
Something
I will add that if we do not have an instance namespace, Django will probably warn us:
WARNINGS: ?: (urls.W005) URL namespace 'english' isn't unique. You may
not be able to reverse all URLs in this namespace
In general, the instance namespace is useful when, for example:
we want to have different URLs depending on the user's native language, such as: 'django/documentation/', 'django/dokumentacja/' or 'django/en', 'django/pl'
we want to separate URLs for specific groups of people: 'amazon/clients/', 'amazon/employees'
we have changed the URL of the website and to not confuse old users, we also allow access to the site via the previous link
we make it easier to find our site on the internet
This is not limited to different URLs. Even though we use the same views, we can slightly modify them depending on the URL we are on:
def index(request):
current_url = request.path
if current_url == '/url1/words/':
''' do something '''
elif current_url == '/url2/words/':
''' do something else '''
return render(request, 'template.html')
We can, for example, change the context or choose a different template.

Django - is not a registered namespace

I am trying to process a form in django/python using the following code.
home.html:
<form action="{% url 'home:submit' %}" method='post'>
views.py:
def submit(request):
a = request.POST(['initial'])
return render(request, 'home/home.html', {
'error_message': "returned"
})
urls.py:
from django.conf.urls import url
from . import views
urlpatterns = [
url(r'^submit/$', views.submit, name='submit')
]
when I try to run it in a browser I get the error:
NoReverseMatch at /home/ u'home' is not a registered namespace
and another error message indicating a problem with the form.

You should just change you action url in your template:
<form action="{% url 'submit' %} "method='post'>
On the note of url namespaces...
In order to be able to call urls using home namespace you should have in your main urls.py file line something like:
for django 1.x:
url(r'^', include('home.urls', namespace='home')),
for django 2.x and 3.x
path('', include(('home.urls', 'home'), namespace='home'))

In your main project, open url.py first. Then check, there should be app_name declared at first. If it is not, declare it.
For example, my app name is user info which is declared in url.py
app_name = "userinfo"
urlpatterns = [
url(r'home/', views.home, name='home'),
url(r'register/', views.registration, name='register')
]

I also faced the same issue.
it is fixed now by adding
app_name = "<name of your app>"
in app/urls.py

For Django 3.0, if you're handling your urls within the app and using include with path, in your project/urls.py:
urlpatterns = [
path(os.getenv('ADMIN_PATH'), admin.site.urls),
path('', include('my_simple_blog.urls', namespace='my_simple_blog')),
path('account/', include('account.urls', namespace='account')),
]
You need to specify namespace in include.
And then in your app/urls.py:
app_name = 'account'
urlpatterns = [
path('register/', registration_view, name='register'),
path('logout/', logout_view, name='logout'),
path('login/', login_view, name='login'),
]
The app_name must match the namespace you've specified in project/urls.py.
Whenever you're referring to these urls, you need to do it like this:
{% url 'namespace:name' %}
If you're using it with redirect:
return redirect('namespace:name')

For the namespace error,
Make sure you have linked the app's url in the main urls.py file
path('app_name/',include('app_name.urls'))
also in the urls.py of your app,make sure you mention the app's name as
app_name='app_name'
Also make sure you have registered the app's name on your installed apps in settings.py

As azmirfakkri has said if you're using redirect, dont use this {% url 'namespace:name' %} syntax, use return redirect('namespace:name').

Probably 2 things could be a root cause,
in app/urls.py do include as below
app_name = 'required_name'
and in project urls.py also include the app_name
url(r'^required_name/$',views.home,name='required_name'),
Check: register app in settings.py INSTALLED_APPS

tag name must be unique in the urls.py file inside your application package inside the project! it is important for the template tagging to route whats what and where.
now [1] inside the urls.py file you need to declare the variable appName and give it the unique value. for example appName = "myApp"; in your case myHomeApp and [2] also define the urlpatterns list...
urlpatterns = [..., url(r'^submit/$', views.submit, name='submit'), ...];
in the html file just change the url tag to:
<form action="{% url 'myHomeApp:submit' %}" method='post'>
this should sifuce... else just write here and we'll see how to continue on

A common mistake that I always find is when you have some name space in your template,
and in YourApp.url you don't have any name space so if you should use name space add
in YourApp.url something like this
app_name = "blog"
then on your temples make sure you add your name space,
so you will have some thing like this "assumption errors are coming from edit.html"
then on that particular template you will do this
"{% url 'blog:vote' pk=post.pk %}" "{% url 'blog:post_category' category.name %}"

if you happen to be nesting include(s, the namespace compounds, eg. topappname:appname:viewname

Maybe someone will find this suggestion helpful.
Go to your applications urls.py and type this before the urlpatterns:
app_name = 'Your app name'

I got the same error below:
NoReverseMatch at /account/register/ 'account' is not a registered
namespace
So, I set "app_name" with the application name "account" to "account/urls.py" as shown below then the error above is solved:
# "account/urls.py"
from django.urls import path
from . import views
app_name = "account" # Here
urlpatterns = [
path("register/", views.register_request, name="register")
]

Check your urls.py
urlpatterns = [
re_path(r'^submit/expense/$', views.submit_expense, name='submit_expense'),
re_path(r'^submit/income/$', views.submit_income, name='submit_income'),
re_path(r'^register/$', views.register, name='register'),
]
then open template.html
put for example register register in your HTML tag like this:
<a class="navbar-brand" href="{% url 'register' %}">

For anyone who struggled on this error like me: After reading the solutions to this question, I was setting namespace in include function in a wrong urls file. Make sure you are modifying the right urls file. For me it was putting it in the main url.py besides settings.py. I hope this answer helps anyone who was confused as I was.

This worked for me:
In urls.py
urlpatterns = [
path("admin/", admin.site.urls),
path("", views.index),
path("test/", views.test, name = 'test')]
In views.py:
def test(request):
return render(request, "base/test.html")
In the template:
href="{% url 'test' %}"

Django named routes like Laravel

I'm starting to learn about Django Framework. I have this urls in my urls.py
from django.conf.urls import patterns, include, url
urlpatterns = patterns('',
# Examples:
url(r'^hello/$','article.views.hello'),
)
My questions are: Can I give this routes a name, like i would in Laravel? How can i reference those named routes from template?
Thanks!

Yes, you can:
url(r'^hello/$','article.views.hello', name="hello"),
You would reference it in a template as:
{% url 'hello' %}
For more information, including how to give arguments to a named URL, see here.