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

URL dispatcher

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

.. module:: django.core.urlresolvers

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.

There's no ``.php`` or ``.cgi`` required, and certainly none of that

``0,2097,1-1-1928,00`` nonsense.

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: http://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 simple mapping between URL patterns (as simple regular expressions) to

Python callback 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.

.. _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:

    1. 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 an attribute called ``urlconf`` (set by

       middleware :ref:`request processing <request-middleware>`), its value

       will be used in place of the :setting:`ROOT_URLCONF` setting.

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

       ``urlpatterns``. This should be a Python list, in the format returned by

       the function :func:`django.conf.urls.defaults.patterns`.

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

       one that matches the requested URL.

    4. Once one of the regexes matches, Django imports and calls the given

       view, which is a simple Python function. The view gets passed an

       :class:`~django.http.HttpRequest` as its first argument and any values

       captured in the regex as remaining arguments.

Example

=======

Here's a sample URLconf::

    from django.conf.urls.defaults import *

    urlpatterns = patterns('',

        (r'^articles/2003/$', 'news.views.special_case_2003'),

        (r'^articles/(\d{4})/$', 'news.views.year_archive'),

        (r'^articles/(\d{4})/(\d{2})/$', 'news.views.month_archive'),

        (r'^articles/(\d{4})/(\d{2})/(\d+)/$', 'news.views.article_detail'),

    )

Notes:

    * ``from django.conf.urls.defaults import *`` makes the ``patterns()``

      function available.

    * To capture a value from the URL, just put parenthesis around it.

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

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

    * The ``'r'`` in front of each regular expression string is optional but

      recommended. It tells Python that a string is "raw" -- that nothing in

      the string should be escaped. See `Dive Into Python's explanation`_.

Example requests:

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

      list. Django would call the function

      ``news.views.month_archive(request, '2005', '03')``.

    * ``/articles/2005/3/`` would not match any URL patterns, because the

      third entry in the list requires two digits for the month.

    * ``/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.

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

      pattern requires that the URL end with a slash.

    * ``/articles/2003/03/3/`` would match the final pattern. Django would call

      the function ``news.views.article_detail(request, '2003', '03', '3')``.

.. _Dive Into Python's explanation: http://diveintopython.org/regular_expressions/street_addresses.html#re.matching.2.3

Named groups

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

The above example used simple, *non-named* regular-expression groups (via

parenthesis) to capture bits of the URL and pass them as *positional* arguments

to a view. In more advanced usage, it's possible to use *named*

regular-expression groups to capture URL bits and pass them as *keyword*

arguments to a view.

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 above example URLconf, rewritten to use named groups::

    urlpatterns = patterns('',

        (r'^articles/2003/$', 'news.views.special_case_2003'),

        (r'^articles/(?P<year>\d{4})/$', 'news.views.year_archive'),

        (r'^articles/(?P<year>\d{4})/(?P<month>\d{2})/$', 'news.views.month_archive'),

        (r'^articles/(?P<year>\d{4})/(?P<month>\d{2})/(?P<day>\d+)/$', 'news.views.article_detail'),

    )

This accomplishes exactly the same thing as the previous example, with one

subtle difference: The captured values are passed to view functions as keyword

arguments rather than positional arguments. For example:

    * A request to ``/articles/2005/03/`` would call the function

      ``news.views.month_archive(request, year='2005', month='03')``, instead

      of ``news.views.month_archive(request, '2005', '03')``.

    * A request to ``/articles/2003/03/3/`` would call the function

      ``news.views.article_detail(request, year='2003', month='03', day='3')``.

In practice, this means your URLconfs are slightly more explicit and less prone

to argument-order bugs -- and you can reorder the arguments in your views'

function definitions. Of course, these benefits come at the cost of brevity;

some developers find the named-group syntax ugly and too verbose.

The matching/grouping algorithm

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

Here's the algorithm the URLconf parser follows, with respect to named groups

vs. non-named groups in a regular expression:

If there are any named arguments, it will use those, ignoring non-named arguments.

Otherwise, it will pass all non-named arguments as positional arguments.

In both cases, it will pass any extra keyword arguments as keyword arguments.

See "Passing extra options to view functions" below.

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 ``http://www.example.com/myapp/``, the URLconf

will look for ``myapp/``.

In a request to ``http://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.

Syntax of the urlpatterns variable

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

``urlpatterns`` should be a Python list, in the format returned by the function

:func:`django.conf.urls.defaults.patterns`. Always use ``patterns()`` to create

the ``urlpatterns`` variable.

Convention is to use ``from django.conf.urls.defaults import *`` at the top of

your URLconf. This gives your module access to these objects:

.. module:: django.conf.urls.defaults

patterns

--------

.. function:: patterns(prefix, pattern_description, ...)

A function that takes a prefix, and an arbitrary number of URL patterns, and

returns a list of URL patterns in the format Django needs.

The first argument to ``patterns()`` is a string ``prefix``. See

`The view prefix`_ below.

The remaining arguments should be tuples in this format::

    (regular expression, Python callback function [, optional dictionary [, optional name]])

...where ``optional dictionary`` and ``optional name`` are optional. (See

`Passing extra options to view functions`_ below.)

.. note::

    Because `patterns()` is a function call, it accepts a maximum of 255

    arguments (URL patterns, in this case). This is a limit for all Python

    function calls. This is rarely a problem in practice, because you'll

    typically structure your URL patterns modularly by using `include()`

    sections. However, on the off-chance you do hit the 255-argument limit,

    realize that `patterns()` returns a Python list, so you can split up the

    construction of the list.

    ::

        urlpatterns = patterns('',

            ...

            )

        urlpatterns += patterns('',

            ...

            )

    Python lists have unlimited size, so there's no limit to how many URL

    patterns you can construct. The only limit is that you can only create 254

    at a time (the 255th argument is the initial prefix argument).

url

---

.. versionadded:: 1.0

.. function:: url(regex, view, kwargs=None, name=None, prefix='')

You can use the ``url()`` function, instead of a tuple, as an argument to

``patterns()``. This is convenient if you want to specify a name without the

optional extra arguments dictionary. For example::

    urlpatterns = patterns('',

        url(r'^index/$', index_view, name="main-view"),

        ...

    )

This function takes five arguments, most of which are optional::

    url(regex, view, kwargs=None, name=None, prefix='')

See `Naming URL patterns`_ for why the ``name`` parameter is useful.

The ``prefix`` parameter has the same meaning as the first argument to

``patterns()`` and is only relevant when you're passing a string as the

``view`` parameter.

handler404

----------

.. data:: handler404

A callable, or a string representing the full Python import path to the view

that should be called if none of the URL patterns match.

By default, this is ``'django.views.defaults.page_not_found'``. That default

value should suffice.

.. versionchanged:: 1.2

    Previous versions of Django only accepted strings representing import paths.

handler500

----------

.. data:: handler500

A callable, or a string representing the full Python import path to the view

that should be called in case of server errors. Server errors happen when you

have runtime errors in view code.

By default, this is ``'django.views.defaults.server_error'``. That default

value should suffice.

.. versionchanged:: 1.2

    Previous versions of Django only accepted strings representing import paths.

include

-------

.. function:: include(<module or pattern_list>)

A function that takes a full Python import path to another URLconf module that

should be "included" in this place.

.. versionadded:: 1.1

:func:`include` also accepts as an argument an iterable that returns URL

patterns.

See `Including other URLconfs`_ below.

Notes on capturing text in URLs

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

Each captured argument is sent to the view as a plain Python string, regardless

of what sort of match the regular expression makes. For example, in this

URLconf line::

    (r'^articles/(?P<year>\d{4})/$', 'news.views.year_archive'),

...the ``year`` argument to ``news.views.year_archive()`` will be a string, not

an integer, even though the ``\d{4}`` will only match integer strings.

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

Here's an example URLconf and view::

    # URLconf

    urlpatterns = patterns('',

        (r'^blog/$', 'blog.views.page'),

        (r'^blog/page(?P<num>\d+)/$', 'blog.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 --

``blog.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 by the regex.

Performance

===========

Each regular expression in a ``urlpatterns`` is compiled the first time it's

accessed. This makes the system blazingly fast.

The view prefix

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

You can specify a common prefix in your ``patterns()`` call, to cut down on

code duplication.

Here's the example URLconf from the :doc:`Django overview </intro/overview>`::

    from django.conf.urls.defaults import *

    urlpatterns = patterns('',

        (r'^articles/(\d{4})/$', 'news.views.year_archive'),

        (r'^articles/(\d{4})/(\d{2})/$', 'news.views.month_archive'),

        (r'^articles/(\d{4})/(\d{2})/(\d+)/$', 'news.views.article_detail'),

    )

In this example, each view has a common prefix -- ``'news.views'``.

Instead of typing that out for each entry in ``urlpatterns``, you can use the

first argument to the ``patterns()`` function to specify a prefix to apply to

each view function.

With this in mind, the above example can be written more concisely as::

    from django.conf.urls.defaults import *

    urlpatterns = patterns('news.views',

        (r'^articles/(\d{4})/$', 'year_archive'),

        (r'^articles/(\d{4})/(\d{2})/$', 'month_archive'),

        (r'^articles/(\d{4})/(\d{2})/(\d+)/$', 'article_detail'),

    )

Note that you don't put a trailing dot (``"."``) in the prefix. Django puts

that in automatically.

Multiple view prefixes

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

In practice, you'll probably end up mixing and matching views to the point

where the views in your ``urlpatterns`` won't have a common prefix. However,

you can still take advantage of the view prefix shortcut to remove duplication.

Just add multiple ``patterns()`` objects together, like this:

Old::

    from django.conf.urls.defaults import *

    urlpatterns = patterns('',

        (r'^$', 'django.views.generic.date_based.archive_index'),

        (r'^(?P<year>\d{4})/(?P<month>[a-z]{3})/$', 'django.views.generic.date_based.archive_month'),

        (r'^tag/(?P<tag>\w+)/$', 'weblog.views.tag'),

    )

New::

    from django.conf.urls.defaults import *

    urlpatterns = patterns('django.views.generic.date_based',

        (r'^$', 'archive_index'),

        (r'^(?P<year>\d{4})/(?P<month>[a-z]{3})/$','archive_month'),

    )

    urlpatterns += patterns('weblog.views',

        (r'^tag/(?P<tag>\w+)/$', 'tag'),

    )

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 the URLconf for the `Django Web site`_ itself. It includes a

number of other URLconfs::

    from django.conf.urls.defaults import *

    urlpatterns = patterns('',

        (r'^weblog/',        include('django_website.apps.blog.urls.blog')),

        (r'^documentation/', include('django_website.apps.docs.urls.docs')),

        (r'^comments/',      include('django.contrib.comments.urls')),

    )

Note that the regular expressions in this example don't have a ``$``

(end-of-string match character) but do include a trailing slash. Whenever

Django encounters ``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.

.. versionadded:: 1.1

Another possibility is to include additional URL patterns not by specifying the

URLconf Python module defining them as the `include`_ argument but by using

directly the pattern list as returned by `patterns`_ instead. For example::

    from django.conf.urls.defaults import *

    extra_patterns = patterns('',

        url(r'reports/(?P<id>\d+)/$', 'credit.views.report', name='credit-reports'),

        url(r'charge/$', 'credit.views.charge', name='credit-charge'),

    )

    urlpatterns = patterns('',

        url(r'^$',    'apps.main.views.homepage', name='site-homepage'),

        (r'^help/',   include('apps.help.urls')),

        (r'^credit/', include(extra_patterns)),

    )

This approach can be seen in use when you deploy an instance of the Django

Admin application. The Django Admin is deployed as instances of a

:class:`~django.contrib.admin.AdminSite`; each

:class:`~django.contrib.admin.AdminSite` instance has an attribute ``urls``

that returns the url patterns available to that instance. It is this attribute

that you ``include()`` into your projects ``urlpatterns`` when you deploy the

admin instance.

.. _`Django Web site`: http://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

    urlpatterns = patterns('',

        (r'^(?P<username>\w+)/blog/', include('foo.urls.blog')),

    )

    # In foo/urls/blog.py

    urlpatterns = patterns('foo.views',

        (r'^$', 'blog.index'),

        (r'^archive/$', 'blog.archive'),

    )

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

included URLconf, as expected.

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

Defining URL Namespaces

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

When you need to deploy multiple instances of a single application, it can be

helpful to be able to differentiate between instances. This is especially

important when using :ref:`named URL patterns <naming-url-patterns>`, since

multiple instances of a single application will share named URLs. Namespaces

provide a way to tell these named URLs apart.

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

    * An **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``.

    * An **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``.

URL Namespaces can be specified in two ways.

Firstly, you can provide the application and instance namespace as arguments

to ``include()`` when you construct your URL patterns. For example,::

    (r'^help/', include('apps.help.urls', namespace='foo', app_name='bar')),

This will include the URLs defined in ``apps.help.urls`` into the application

namespace ``bar``, with the instance namespace ``foo``.

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

you ``include()`` a ``patterns`` object, that object will be added to the

global namespace. However, you can also ``include()`` an object that contains

a 3-tuple containing::

    (<patterns object>, <application namespace>, <instance namespace>)

This will include the nominated URL patterns into the given application and

instance namespace. For example, the ``urls`` attribute of Django's

:class:`~django.contrib.admin.AdminSite` object returns a 3-tuple that contains

all the patterns in an admin site, plus the name of the admin instance, and the

application namespace ``admin``.

Once you have defined namespaced URLs, you can reverse them. For details on

reversing namespaced urls, see the documentation on :ref:`reversing namespaced

URLs <topics-http-reversing-url-namespaces>`.

Passing extra options to view functions

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

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

as a Python dictionary.

Any URLconf tuple can have an optional third element, which should be a

dictionary of extra keyword arguments to pass to the view function.