A real example of URL Namespace

Question

I am studying the Django documentation, but I encountered a part that I cannot understand: what is a real example of how use to use a namespace in a real problem. I know the syntax but I do not know the purpose of this.

Answer 1

Typically, they are used to put each application's URLs into their own namespace. This prevents the reverse() Django function and the {% url %} template function from returning the wrong URL because the URL-pattern name happened to match in another app.

What I have in my project-level urls.py file is the following:

from django.conf.urls.defaults import *
from django.conf import settings
from django.contrib import admin
admin.autodiscover()

urlpatterns = patterns('',
    url(r'^$', 'main.views.main', name='main'),
    url(r'^login$', 'django.contrib.auth.views.login', name="login"),
    url(r'^logout$', 'django.contrib.auth.views.logout',
        {"next_page": "/"}, name="logout"),

# Admin
    url(r'^admin/doc/', include('django.contrib.admindocs.urls')),
    url(r'^admin/', include(admin.site.urls)),
)

# Auto-add the applications.
for app in settings.LOCAL_APPS:
    urlpatterns += patterns('',
        url(r'^{0}/'.format(app), include(app + '.urls', namespace=app)),
    )

Note the last section: this goes through the applications I have installed (settings.LOCAL_APPS is a setting I added that contains only my apps; it gets added to INSTALLED_APPS which has other things like South), looks for a urls.py in each of them, and imports those URLs into a namespace named after the app, and also puts those URLs into a URL subdirectory named after the app.

So, for example, if I have an app named hosts, and hosts/urls.py looks like:

from django.conf.urls.defaults import *

urlpatterns = patterns('hosts.views',
    url(r'^$', 'show_hosts', name='list'),
)

Now my views.py can call reverse("hosts:list") to get the URL to the page that calls hosts.views.show_hosts, and it will look something like "/hosts/". Same goes for {% url "hosts:list" %} in a template. This way I don't have to worry about colliding with a URL named "list" in another app, and I don't have to prefix every name with hosts_.

Note that the login page is at {% url "login" %} since it wasn't given a namespace.

Answer 2

Consider you are using a url pattern as below
url(r'^login/',include('app_name', name='login'))

Also Consider you are using a third-party app like Django-RestFramework. When you use the app, you have to declare the following line in URLs conf file of the project.

url(r'^api-auth/', include('rest_framework.urls', namespace='rest_framework'))

Now if you check the code of rest-framework, you will find the below code in urls.py file

urlpatterns = [
    url(r'^login/$', login, login_kwargs, name='login'),
    url(r'^logout/$', logout, name='logout'),
]

We have used 'login' name for a URL pattern in our project and the same name is being used by Django-rest-framework for one of their URL patterns. When you use reverse('login'), Django will get confused.
To resolve these kinds of issues, we use namespace.

@register.simple_tag
def optional_docs_login(request):
    """
    Include a login snippet if REST framework's login view is in the URLconf.
    """
    try:
        login_url = reverse('rest_framework:login')
    except NoReverseMatch:
        return 'log in'

URL names of a namespace will never collide with other namespaces.
A namespaced URL pattern can be reversed using
reverse('namespace:url_name')