==============

URL dispatcher

==============

A clean, elegant URL scheme is an important detail in a high-quality web

application. Django lets you design URLs however you want, with no framework

limitations.

See `Cool URIs don't change`_, by World Wide Web creator Tim Berners-Lee, for

excellent arguments on why URLs should be clean and usable.

.. _Cool URIs don't change: https://www.w3.org/Provider/Style/URI

Overview

========

To design URLs for an app, you create a Python module informally called a

**URLconf** (URL configuration). This module is pure Python code and is a

mapping between URL path expressions to Python functions (your views).

This mapping can be as short or as long as needed. It can reference other

mappings. And, because it's pure Python code, it can be constructed

dynamically.

Django also provides a way to translate URLs according to the active

language. See the :ref:`internationalization documentation

<url-internationalization>` for more information.

.. _how-django-processes-a-request:

How Django processes a request

==============================

When a user requests a page from your Django-powered site, this is the

algorithm the system follows to determine which Python code to execute:

#. Django determines the root URLconf module to use. Ordinarily,

   this is the value of the :setting:`ROOT_URLCONF` setting, but if the incoming

   ``HttpRequest`` object has a :attr:`~django.http.HttpRequest.urlconf`

   attribute (set by middleware), its value will be used in place of the

   :setting:`ROOT_URLCONF` setting.

#. Django loads that Python module and looks for the variable

   ``urlpatterns``. This should be a :term:`sequence` of

   :func:`django.urls.path` and/or :func:`django.urls.re_path` instances.

#. Django runs through each URL pattern, in order, and stops at the first

   one that matches the requested URL, matching against

   :attr:`~django.http.HttpRequest.path_info`.

#. Once one of the URL patterns matches, Django imports and calls the given

   view, which is a Python function (or a :doc:`class-based view

   </topics/class-based-views/index>`). The view gets passed the following

   arguments:

   * An instance of :class:`~django.http.HttpRequest`.

   * If the matched URL pattern contained no named groups, then the

     matches from the regular expression are provided as positional arguments.

   * The keyword arguments are made up of any named parts matched by the

     path expression that are provided, overridden by any arguments specified

     in the optional ``kwargs`` argument to :func:`django.urls.path` or

     :func:`django.urls.re_path`.

#. If no URL pattern matches, or if an exception is raised during any

   point in this process, Django invokes an appropriate

   error-handling view. See `Error handling`_ below.

Example

=======

Here's a sample URLconf::

    from django.urls import path

    from . import views

    urlpatterns = [

        path('articles/2003/', views.special_case_2003),

        path('articles/<int:year>/', views.year_archive),

        path('articles/<int:year>/<int:month>/', views.month_archive),

        path('articles/<int:year>/<int:month>/<slug:slug>/', views.article_detail),

    ]

Notes:

* To capture a value from the URL, use angle brackets.

* Captured values can optionally include a converter type. For example, use

  ``<int:name>`` to capture an integer parameter. If a converter isn't included,

  any string, excluding a ``/`` character, is matched.

* There's no need to add a leading slash, because every URL has that. For

  example, it's ``articles``, not ``/articles``.

Example requests:

* A request to ``/articles/2005/03/`` would match the third entry in the

  list. Django would call the function

  ``views.month_archive(request, year=2005, month=3)``.

* ``/articles/2003/`` would match the first pattern in the list, not the

  second one, because the patterns are tested in order, and the first one

  is the first test to pass. Feel free to exploit the ordering to insert

  special cases like this. Here, Django would call the function

  ``views.special_case_2003(request)``

* ``/articles/2003`` would not match any of these patterns, because each

  pattern requires that the URL end with a slash.

* ``/articles/2003/03/building-a-django-site/`` would match the final

  pattern. Django would call the function

  ``views.article_detail(request, year=2003, month=3, slug="building-a-django-site")``.

Path converters

===============

The following path converters are available by default:

* ``str`` - Matches any non-empty string, excluding the path separator, ``'/'``.

  This is the default if a converter isn't included in the expression.

* ``int`` - Matches zero or any positive integer. Returns an ``int``.

* ``slug`` - Matches any slug string consisting of ASCII letters or numbers,

  plus the hyphen and underscore characters. For example,

  ``building-your-1st-django-site``.

* ``uuid`` - Matches a formatted UUID. To prevent multiple URLs from mapping to

  the same page, dashes must be included and letters must be lowercase. For

  example, ``075194d3-6885-417e-a8a8-6c931e272f00``. Returns a

  :class:`~uuid.UUID` instance.

* ``path`` - Matches any non-empty string, including the path separator,

  ``'/'``. This allows you to match against a complete URL path rather than

  a segment of a URL path as with ``str``.

.. _registering-custom-path-converters:

Registering custom path converters

==================================

For more complex matching requirements, you can define your own path converters.

A converter is a class that includes the following:

* A ``regex`` class attribute, as a string.

* A ``to_python(self, value)`` method, which handles converting the matched

  string into the type that should be passed to the view function. It should

  raise ``ValueError`` if it can't convert the given value. A ``ValueError`` is

  interpreted as no match and as a consequence a 404 response is sent to the

  user unless another URL pattern matches.

* A ``to_url(self, value)`` method, which handles converting the Python type

  into a string to be used in the URL. It should raise ``ValueError`` if it

  can't convert the given value. A ``ValueError`` is interpreted as no match

  and as a consequence :func:`~django.urls.reverse` will raise

  :class:`~django.urls.NoReverseMatch` unless another URL pattern matches.

For example::

    class FourDigitYearConverter:

        regex = '[0-9]{4}'

        def to_python(self, value):

            return int(value)

        def to_url(self, value):

            return '%04d' % value

Register custom converter classes in your URLconf using

:func:`~django.urls.register_converter`::

    from django.urls import path, register_converter

    from . import converters, views

    register_converter(converters.FourDigitYearConverter, 'yyyy')

    urlpatterns = [

        path('articles/2003/', views.special_case_2003),

        path('articles/<yyyy:year>/', views.year_archive),

        ...

    ]

Using regular expressions

=========================

If the paths and converters syntax isn't sufficient for defining your URL

patterns, you can also use regular expressions. To do so, use

:func:`~django.urls.re_path` instead of :func:`~django.urls.path`.

In Python regular expressions, the syntax for named regular expression groups

is ``(?P<name>pattern)``, where ``name`` is the name of the group and

``pattern`` is some pattern to match.

Here's the example URLconf from earlier, rewritten using regular expressions::

    from django.urls import path, re_path

    from . import views

    urlpatterns = [

        path('articles/2003/', views.special_case_2003),

        re_path(r'^articles/(?P<year>[0-9]{4})/$', views.year_archive),

        re_path(r'^articles/(?P<year>[0-9]{4})/(?P<month>[0-9]{2})/$', views.month_archive),

        re_path(r'^articles/(?P<year>[0-9]{4})/(?P<month>[0-9]{2})/(?P<slug>[\w-]+)/$', views.article_detail),

    ]

This accomplishes roughly the same thing as the previous example, except:

* The exact URLs that will match are slightly more constrained. For example,

  the year 10000 will no longer match since the year integers are constrained

  to be exactly four digits long.

* Each captured argument is sent to the view as a string, regardless of what

  sort of match the regular expression makes.

When switching from using :func:`~django.urls.path` to

:func:`~django.urls.re_path` or vice versa, it's particularly important to be

aware that the type of the view arguments may change, and so you may need to

adapt your views.

Using unnamed regular expression groups

---------------------------------------

As well as the named group syntax, e.g. ``(?P<year>[0-9]{4})``, you can

also use the shorter unnamed group, e.g. ``([0-9]{4})``.

This usage isn't particularly recommended as it makes it easier to accidentally

introduce errors between the intended meaning of a match and the arguments

of the view.

In either case, using only one style within a given regex is recommended. When

both styles are mixed, any unnamed groups are ignored and only named groups are

passed to the view function.

Nested arguments

----------------

Regular expressions allow nested arguments, and Django will resolve them and

pass them to the view. When reversing, Django will try to fill in all outer

captured arguments, ignoring any nested captured arguments. Consider the

following URL patterns which optionally take a page argument::

    from django.urls import re_path

    urlpatterns = [

        re_path(r'^blog/(page-([0-9]+)/)?$', blog_articles),                  # bad

        re_path(r'^comments/(?:page-(?P<page_number>[0-9]+)/)?$', comments),  # good

    ]

Both patterns use nested arguments and will resolve: for example,

``blog/page-2/`` will result in a match to ``blog_articles`` with two

positional arguments: ``page-2/`` and ``2``. The second pattern for

``comments`` will match ``comments/page-2/`` with keyword argument

``page_number`` set to 2. The outer argument in this case is a non-capturing

argument ``(?:...)``.

The ``blog_articles`` view needs the outermost captured argument to be reversed,

``page-2/`` or no arguments in this case, while ``comments`` can be reversed

with either no arguments or a value for ``page_number``.

Nested captured arguments create a strong coupling between the view arguments

and the URL as illustrated by ``blog_articles``: the view receives part of the

URL (``page-2/``) instead of only the value the view is interested in. This

coupling is even more pronounced when reversing, since to reverse the view we

need to pass the piece of URL instead of the page number.

As a rule of thumb, only capture the values the view needs to work with and

use non-capturing arguments when the regular expression needs an argument but

the view ignores it.

What the URLconf searches against

=================================

The URLconf searches against the requested URL, as a normal Python string. This

does not include GET or POST parameters, or the domain name.

For example, in a request to ``https://www.example.com/myapp/``, the URLconf

will look for ``myapp/``.

In a request to ``https://www.example.com/myapp/?page=3``, the URLconf will look

for ``myapp/``.

The URLconf doesn't look at the request method. In other words, all request

methods -- ``POST``, ``GET``, ``HEAD``, etc. -- will be routed to the same

function for the same URL.

Specifying defaults for view arguments

======================================

A convenient trick is to specify default parameters for your views' arguments.

Here's an example URLconf and view::

    # URLconf

    from django.urls import path

    from . import views

    urlpatterns = [

        path('blog/', views.page),

        path('blog/page<int:num>/', views.page),

    ]

    # View (in blog/views.py)

    def page(request, num=1):

        # Output the appropriate page of blog entries, according to num.

        ...

In the above example, both URL patterns point to the same view --

``views.page`` -- but the first pattern doesn't capture anything from the

URL. If the first pattern matches, the ``page()`` function will use its

default argument for ``num``, ``1``. If the second pattern matches,

``page()`` will use whatever ``num`` value was captured.

Performance

===========

Django processes regular expressions in the ``urlpatterns`` list which is

compiled the first time it's accessed. Subsequent requests use the cached

configuration via the URL resolver.

Syntax of the ``urlpatterns`` variable

======================================

``urlpatterns`` should be a :term:`sequence` of :func:`~django.urls.path`

and/or :func:`~django.urls.re_path` instances.

Error handling

==============

When Django can't find a match for the requested URL, or when an exception is

raised, Django invokes an error-handling view.

The views to use for these cases are specified by four variables. Their

default values should suffice for most projects, but further customization is

possible by overriding their default values.

See the documentation on :ref:`customizing error views

<customizing-error-views>` for the full details.

Such values can be set in your root URLconf. Setting these variables in any

other URLconf will have no effect.

Values must be callables, or strings representing the full Python import path

to the view that should be called to handle the error condition at hand.

The variables are:

* ``handler400`` -- See :data:`django.conf.urls.handler400`.

* ``handler403`` -- See :data:`django.conf.urls.handler403`.

* ``handler404`` -- See :data:`django.conf.urls.handler404`.

* ``handler500`` -- See :data:`django.conf.urls.handler500`.

.. _including-other-urlconfs:

Including other URLconfs

========================

At any point, your ``urlpatterns`` can "include" other URLconf modules. This

essentially "roots" a set of URLs below other ones.

For example, here's an excerpt of the URLconf for the `Django website`_

itself. It includes a number of other URLconfs::

    from django.urls import include, path

    urlpatterns = [

        # ... snip ...

        path('community/', include('aggregator.urls')),

        path('contact/', include('contact.urls')),

        # ... snip ...

    ]

Whenever Django encounters :func:`~django.urls.include()`, it chops off

whatever part of the URL matched up to that point and sends the remaining

string to the included URLconf for further processing.

Another possibility is to include additional URL patterns by using a list of

:func:`~django.urls.path` instances. For example, consider this URLconf::

    from django.urls import include, path

    from apps.main import views as main_views

    from credit import views as credit_views

    extra_patterns = [

        path('reports/', credit_views.report),

        path('reports/<int:id>/', credit_views.report),

        path('charge/', credit_views.charge),

    ]

    urlpatterns = [

        path('', main_views.homepage),

        path('help/', include('apps.help.urls')),

        path('credit/', include(extra_patterns)),

    ]

In this example, the ``/credit/reports/`` URL will be handled by the

``credit_views.report()`` Django view.

This can be used to remove redundancy from URLconfs where a single pattern

prefix is used repeatedly. For example, consider this URLconf::

    from django.urls import path

    from . import views

    urlpatterns = [

        path('<page_slug>-<page_id>/history/', views.history),

        path('<page_slug>-<page_id>/edit/', views.edit),

        path('<page_slug>-<page_id>/discuss/', views.discuss),

        path('<page_slug>-<page_id>/permissions/', views.permissions),

    ]

We can improve this by stating the common path prefix only once and grouping

the suffixes that differ::

    from django.urls import include, path

    from . import views

    urlpatterns = [

        path('<page_slug>-<page_id>/', include([

            path('history/', views.history),

            path('edit/', views.edit),

            path('discuss/', views.discuss),

            path('permissions/', views.permissions),

        ])),

    ]

.. _`Django website`: https://www.djangoproject.com/

Captured parameters

-------------------

An included URLconf receives any captured parameters from parent URLconfs, so

the following example is valid::

    # In settings/urls/main.py

    from django.urls import include, path

    urlpatterns = [

        path('<username>/blog/', include('foo.urls.blog')),

    ]

    # In foo/urls/blog.py

    from django.urls import path

    from . import views

    urlpatterns = [

        path('', views.blog.index),

        path('archive/', views.blog.archive),

    ]

In the above example, the captured ``"username"`` variable is passed to the

included URLconf, as expected.

.. _views-extra-options:

Passing extra options to view functions

=======================================

URLconfs have a hook that lets you pass extra arguments to your view functions,

as a Python dictionary.

The :func:`~django.urls.path` function can take an optional third argument

which should be a dictionary of extra keyword arguments to pass to the view

function.

For example::

    from django.urls import path

    from . import views

    urlpatterns = [

        path('blog/<int:year>/', views.year_archive, {'foo': 'bar'}),

    ]

In this example, for a request to ``/blog/2005/``, Django will call

``views.year_archive(request, year=2005, foo='bar')``.

This technique is used in the

:doc:`syndication framework </ref/contrib/syndication>` to pass metadata and

options to views.

.. admonition:: Dealing with conflicts

    It's possible to have a URL pattern which captures named keyword arguments,

    and also passes arguments with the same names in its dictionary of extra

    arguments. When this happens, the arguments in the dictionary will be used

    instead of the arguments captured in the URL.

Passing extra options to ``include()``

--------------------------------------

Similarly, you can pass extra options to :func:`~django.urls.include` and

each line in the included URLconf will be passed the extra options.

For example, these two URLconf sets are functionally identical:

Set one::

    # main.py

    from django.urls import include, path

    urlpatterns = [

        path('blog/', include('inner'), {'blog_id': 3}),

    ]

    # inner.py

    from django.urls import path

    from mysite import views

    urlpatterns = [

        path('archive/', views.archive),

        path('about/', views.about),

    ]

Set two::

    # main.py

    from django.urls import include, path

    from mysite import views

    urlpatterns = [

        path('blog/', include('inner')),

    ]

    # inner.py

    from django.urls import path

    urlpatterns = [

        path('archive/', views.archive, {'blog_id': 3}),

        path('about/', views.about, {'blog_id': 3}),

    ]

Note that extra options will *always* be passed to *every* line in the included

URLconf, regardless of whether the line's view actually accepts those options

as valid. For this reason, this technique is only useful if you're certain that

every view in the included URLconf accepts the extra options you're passing.

Reverse resolution of URLs

==========================

A common need when working on a Django project is the possibility to obtain URLs

in their final forms either for embedding in generated content (views and assets

URLs, URLs shown to the user, etc.) or for handling of the navigation flow on

the server side (redirections, etc.)

It is strongly desirable to avoid hard-coding these URLs (a laborious,

non-scalable and error-prone strategy). Equally dangerous is devising ad-hoc

mechanisms to generate URLs that are parallel to the design described by the

URLconf, which can result in the production of URLs that become stale over time.

In other words, what's needed is a DRY mechanism. Among other advantages it

would allow evolution of the URL design without having to go over all the

project source code to search and replace outdated URLs.

The primary piece of information we have available to get a URL is an

identification (e.g. the name) of the view in charge of handling it. Other

pieces of information that necessarily must participate in the lookup of the

right URL are the types (positional, keyword) and values of the view arguments.

Django provides a solution such that the URL mapper is the only repository of

the URL design. You feed it with your URLconf and then it can be used in both

directions:

* Starting with a URL requested by the user/browser, it calls the right Django

  view providing any arguments it might need with their values as extracted from

  the URL.

* Starting with the identification of the corresponding Django view plus the

  values of arguments that would be passed to it, obtain the associated URL.

The first one is the usage we've been discussing in the previous sections. The

second one is what is known as *reverse resolution of URLs*, *reverse URL

matching*, *reverse URL lookup*, or simply *URL reversing*.

Django provides tools for performing URL reversing that match the different

layers where URLs are needed:

* In templates: Using the :ttag:`url` template tag.

* In Python code: Using the :func:`~django.urls.reverse` function.

* In higher level code related to handling of URLs of Django model instances:

  The :meth:`~django.db.models.Model.get_absolute_url` method.

Examples

--------

Consider again this URLconf entry::

    from django.urls import path

    from . import views

    urlpatterns = [

        #...

        path('articles/<int:year>/', views.year_archive, name='news-year-archive'),

        #...

    ]

According to this design, the URL for the archive corresponding to year *nnnn*

is ``/articles/<nnnn>/``.

You can obtain these in template code by using:

.. code-block:: html+django

    <a href="{% url 'news-year-archive' 2012 %}">2012 Archive</a>

    {# Or with the year in a template context variable: #}

    <ul>

    {% for yearvar in year_list %}

    <li><a href="{% url 'news-year-archive' yearvar %}">{{ yearvar }} Archive</a></li>

    {% endfor %}

    </ul>

Or in Python code::

    from django.http import HttpResponseRedirect

    from django.urls import reverse

    def redirect_to_year(request):

        # ...

        year = 2006

        # ...

        return HttpResponseRedirect(reverse('news-year-archive', args=(year,)))

If, for some reason, it was decided that the URLs where content for yearly

article archives are published at should be changed then you would only need to

change the entry in the URLconf.

In some scenarios where views are of a generic nature, a many-to-one

relationship might exist between URLs and views. For these cases the view name

isn't a good enough identifier for it when comes the time of reversing

URLs. Read the next section to know about the solution Django provides for this.

.. _naming-url-patterns:

Naming URL patterns

===================

In order to perform URL reversing, you'll need to use **named URL patterns**

as done in the examples above. The string used for the URL name can contain any

characters you like. You are not restricted to valid Python names.

When naming URL patterns, choose names that are unlikely to clash with other

applications' choice of names. If you call your URL pattern ``comment``

and another application does the same thing, the URL that

:func:`~django.urls.reverse()` finds depends on whichever pattern is last in

your project's ``urlpatterns`` list.

Putting a prefix on your URL names, perhaps derived from the application

name (such as ``myapp-comment`` instead of ``comment``), decreases the chance

of collision.

You can deliberately choose the *same URL name* as another application if you

want to override a view. For example, a common use case is to override the

:class:`~django.contrib.auth.views.LoginView`. Parts of Django and most

third-party apps assume that this view has a URL pattern with the name

``login``. If you have a custom login view and give its URL the name ``login``,

:func:`~django.urls.reverse()` will find your custom view as long as it's in

``urlpatterns`` after ``django.contrib.auth.urls`` is included (if that's

included at all).

You may also use the same name for multiple URL patterns if they differ in

their arguments. In addition to the URL name, :func:`~django.urls.reverse()`

matches the number of arguments and the names of the keyword arguments. Path

converters can also raise ``ValueError`` to indicate no match, see

:ref:`registering-custom-path-converters` for details.

.. _topics-http-defining-url-namespaces:

URL namespaces

==============

Introduction

------------

URL namespaces allow you to uniquely reverse :ref:`named URL patterns

<naming-url-patterns>` even if different applications use the same URL names.

It's a good practice for third-party apps to always use namespaced URLs (as we

did in the tutorial). Similarly, it also allows you to reverse URLs if multiple

instances of an application are deployed. In other words, since multiple

instances of a single application will share named URLs, namespaces provide a

way to tell these named URLs apart.

Django applications that make proper use of URL namespacing can be deployed

more than once for a particular site. For example :mod:`django.contrib.admin`

has an :class:`~django.contrib.admin.AdminSite` class which allows you to

:ref:`deploy more than one instance of the admin <multiple-admin-sites>`.  In a

later example, we'll discuss the idea of deploying the polls application from

the tutorial in two different locations so we can serve the same functionality

to two different audiences (authors and publishers).

A URL namespace comes in two parts, both of which are strings:

.. glossary::

  application namespace

    This describes the name of the application that is being deployed. Every

    instance of a single application will have the same application namespace.

    For example, Django's admin application has the somewhat predictable

    application namespace of ``'admin'``.

  instance namespace

    This identifies a specific instance of an application. Instance namespaces

    should be unique across your entire project. However, an instance namespace

    can be the same as the application namespace. This is used to specify a

    default instance of an application. For example, the default Django admin

    instance has an instance namespace of ``'admin'``.

Namespaced URLs are specified using the ``':'`` operator. For example, the main

index page of the admin application is referenced using ``'admin:index'``. This

indicates a namespace of ``'admin'``, and a named URL of ``'index'``.

Namespaces can also be nested. The named URL ``'sports:polls:index'`` would

look for a pattern named ``'index'`` in the namespace ``'polls'`` that is itself

defined within the top-level namespace ``'sports'``.

.. _topics-http-reversing-url-namespaces:

Reversing namespaced URLs

-------------------------

When given a namespaced URL (e.g. ``'polls:index'``) to resolve, Django splits

the fully qualified name into parts and then tries the following lookup:

#. First, Django looks for a matching :term:`application namespace` (in this

   example, ``'polls'``). This will yield a list of instances of that

   application.

#. If there is a current application defined, Django finds and returns the URL

   resolver for that instance. The current application can be specified with

   the ``current_app`` argument to the :func:`~django.urls.reverse()`

   function.

   The :ttag:`url` template tag uses the namespace of the currently resolved

   view as the current application in a

   :class:`~django.template.RequestContext`. You can override this default by

   setting the current application on the :attr:`request.current_app

   <django.http.HttpRequest.current_app>` attribute.

#. If there is no current application, Django looks for a default

   application instance. The default application instance is the instance

   that has an :term:`instance namespace` matching the :term:`application

   namespace` (in this example, an instance of ``polls`` called ``'polls'``).

#. If there is no default application instance, Django will pick the last

   deployed instance of the application, whatever its instance name may be.

#. If the provided namespace doesn't match an :term:`application namespace` in

   step 1, Django will attempt a direct lookup of the namespace as an

   :term:`instance namespace`.

If there are nested namespaces, these steps are repeated for each part of the

namespace until only the view name is unresolved. The view name will then be

resolved into a URL in the namespace that has been found.

Example

~~~~~~~

To show this resolution strategy in action, consider an example of two instances

of the ``polls`` application from the tutorial: one called ``'author-polls'``

and one called ``'publisher-polls'``. Assume we have enhanced that application

so that it takes the instance namespace into consideration when creating and

displaying polls.

.. code-block:: python

    :caption: ``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')),

    ]

.. code-block:: python

    :caption: ``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'),

        ...

    ]

Using this setup, the following lookups are possible:

* If one of the instances is current - say, if we were rendering the detail page

  in the instance ``'author-polls'`` - ``'polls:index'`` will resolve to the

  index page of the ``'author-polls'`` instance; i.e. both of the following will

  result in ``"/author-polls/"``.

  In the method of a class-based view::

    reverse('polls:index', current_app=self.request.resolver_match.namespace)

  and in the template:

  .. code-block:: html+django

    {% url 'polls:index' %}

* If there is no current instance - say, if we were rendering a page

  somewhere else on the site - ``'polls:index'`` will resolve to the last

  registered instance of ``polls``. Since there is no default instance

  (instance namespace of ``'polls'``), the last instance of ``polls`` that is

  registered will be used. This would be ``'publisher-polls'`` since it's

  declared last in the ``urlpatterns``.

* ``'author-polls:index'`` will always resolve to the index page of the instance

  ``'author-polls'`` (and likewise for ``'publisher-polls'``) .

If there were also a default instance - i.e., an instance named ``'polls'`` -

the only change from above would be in the case where there is no current

instance (the second item in the list above). In this case ``'polls:index'``

would resolve to the index page of the default instance instead of the instance

declared last in ``urlpatterns``.

.. _namespaces-and-include:

URL namespaces and included URLconfs

------------------------------------

Application namespaces of included URLconfs can be specified in two ways.

Firstly, you can set an ``app_name`` attribute in the included URLconf module,

at the same level as the ``urlpatterns`` attribute. You have to pass the actual

module, or a string reference to the module, to :func:`~django.urls.include`,

not the list of ``urlpatterns`` itself.

.. code-block:: python

    :caption: ``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'),

        ...

    ]

.. code-block:: python

    :caption: ``urls.py``

    from django.urls import include, path

    urlpatterns = [

        path('polls/', include('polls.urls')),

    ]

The URLs defined in ``polls.urls`` will have an application namespace ``polls``.

Secondly, you can include an object that contains embedded namespace data. If

you ``include()`` a list of :func:`~django.urls.path` or

:func:`~django.urls.re_path` instances, the URLs contained in that object

will be added to the global namespace. However, you can also ``include()`` a

2-tuple containing::

    (<list of path()/re_path() instances>, <application namespace>)

For example::

    from django.urls import include, path

    from . import views

    polls_patterns = ([

        path('', views.IndexView.as_view(), name='index'),

        path('<int:pk>/', views.DetailView.as_view(), name='detail'),

    ], 'polls')

    urlpatterns = [

        path('polls/', include(polls_patterns)),

    ]

This will include the nominated URL patterns into the given application

namespace.

The instance namespace can be specified using the ``namespace`` argument to

:func:`~django.urls.include`. If the instance namespace is not specified,

it will default to the included URLconf's application namespace. This means

it will also be the default instance for that namespace.