============== 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 (simple regular 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. .. versionadded:: 1.4 Django also provides a way to translate URLs according to the active language. See the :ref:`internationalization documentation ` 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: 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 `), 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.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 (or a :doc:`class based view `). The view gets passed an :class:`~django.http.HttpRequest` as its first argument and any values captured in the regex as remaining arguments. 5. If no regex 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.conf.urls import patterns, url, include 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: * 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/2003/03/03/`` would match the final pattern. Django would call the function ``news.views.article_detail(request, '2003', '03', '03')``. .. _Dive Into Python's explanation: http://diveintopython.net/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 ``(?Ppattern)``, 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/$', 'news.views.special_case_2003'), (r'^articles/(?P\d{4})/$', 'news.views.year_archive'), (r'^articles/(?P\d{4})/(?P\d{2})/$', 'news.views.month_archive'), (r'^articles/(?P\d{4})/(?P\d{2})/(?P\d{2})/$', '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/2003/03/03/`` would call the function ``news.views.article_detail(request, year='2003', month='03', day='03')``. 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: 1. If there are any named arguments, it will use those, ignoring non-named arguments. 2. Otherwise, it will pass all non-named arguments as positional arguments. In both cases, any extra keyword arguments that have been given as per `Passing extra options to view functions`_ (below) will also be passed to the view. 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. 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\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\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. Syntax of the urlpatterns variable ================================== ``urlpatterns`` should be a Python list, in the format returned by the function :func:`django.conf.urls.patterns`. Always use ``patterns()`` to create the ``urlpatterns`` variable. ``django.conf.urls`` utility functions ====================================== .. module:: django.conf.urls .. deprecated:: 1.4 Starting with Django 1.4 functions ``patterns``, ``url``, ``include`` plus the ``handler*`` symbols described below live in the ``django.conf.urls`` module. Until Django 1.3 they were located in ``django.conf.urls.defaults``. You still can import them from there but it will be removed in Django 1.6. 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]]) The ``optional_dictionary`` and ``optional_name`` parameters are described in `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 --- .. 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. include ------- .. function:: include() A function that takes a full Python import path to another URLconf module that should be "included" in this place. :func:`include` also accepts as an argument an iterable that returns URL patterns. See `Including other URLconfs`_ below. Error handling ============== When Django can't find a regex matching the requested URL, or when an exception is raised, Django will invoke an error-handling view. The views to use for these cases are specified by three variables which can be set in your root URLconf. Setting these variables in any other URLconf will have no effect. See the documentation on :ref:`customizing error views ` for more details. handler403 ---------- .. data:: handler403 A callable, or a string representing the full Python import path to the view that should be called if the user doesn't have the permissions required to access a resource. By default, this is ``'django.views.defaults.permission_denied'``. That default value should suffice. See the documentation about :ref:`the 403 (HTTP Forbidden) view ` for more information. .. versionadded:: 1.4 ``handler403`` is new in Django 1.4. 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. See the documentation about :ref:`the 404 (HTTP Not Found) view ` for more information. 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. See the documentation about :ref:`the 500 (HTTP Internal Server Error) view ` for more information. 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 `:: from django.conf.urls import patterns, url, include 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+)/$', 'news.views.article_detail'), ) In this example, each view has a common prefix -- ``'news.views'``. Instead of typing that out for each entry in ``urlpatterns``, you can use the first argument to the ``patterns()`` function to specify a prefix to apply to each view function. With this in mind, the above example can be written more concisely as:: from django.conf.urls import patterns, url, include urlpatterns = patterns('news.views', (r'^articles/(\d{4})/$', '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 import patterns, url, include urlpatterns = patterns('', (r'^$', 'myapp.views.app_index'), (r'^(?P\d{4})/(?P[a-z]{3})/$', 'myapp.views.month_display'), (r'^tag/(?P\w+)/$', 'weblog.views.tag'), ) New:: from django.conf.urls import patterns, url, include urlpatterns = patterns('myapp.views', (r'^$', 'app_index'), (r'^(?P\d{4})/(?P[a-z]{3})/$','month_display'), ) urlpatterns += patterns('weblog.views', (r'^tag/(?P\w+)/$', '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 an excerpt of the URLconf for the `Django Web site`_ itself. It includes a number of other URLconfs:: from django.conf.urls import patterns, url, include urlpatterns = patterns('', # ... snip ... (r'^comments/', include('django.contrib.comments.urls')), (r'^community/', include('django_website.aggregator.urls')), (r'^contact/', include('django_website.contact.urls')), (r'^r/', include('django.conf.urls.shortcut')), # ... snip ... ) Note that the regular expressions in this example don't have a ``$`` (end-of-string match character) but do include a trailing slash. Whenever Django encounters ``include()``, it chops off whatever part of the URL matched up to that point and sends the remaining string to the included URLconf for further processing. Another possibility is to include additional URL patterns not by specifying the URLconf Python module defining them as the `include`_ argument but by using directly the pattern list as returned by `patterns`_ instead. For example:: from django.conf.urls import patterns, url, include extra_patterns = patterns('', url(r'^reports/(?P\d+)/$', '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`: 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 urlpatterns = patterns('', (r'^(?P\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 `, 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:: (, , ) 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 `. 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. For example:: urlpatterns = patterns('blog.views', (r'^blog/(?P\d{4})/$', 'year_archive', {'foo': 'bar'}), ) In this example, for a request to ``/blog/2005/``, Django will call ``blog.views.year_archive(year='2005', foo='bar')``. This technique is used in the :doc:`syndication framework ` to pass metadata and options to views. .. admonition:: Dealing with conflicts It's possible to have a URL pattern which captures named keyword arguments, and also passes arguments with the same names in its dictionary of extra arguments. When this happens, the arguments in the dictionary will be used instead of the arguments captured in the URL. Passing extra options to ``include()`` -------------------------------------- Similarly, you can pass extra options to ``include()``. When you pass extra options to ``include()``, *each* line in the included URLconf will be passed the extra options. For example, these two URLconf sets are functionally identical: Set one:: # main.py urlpatterns = patterns('', (r'^blog/', include('inner'), {'blogid': 3}), ) # inner.py urlpatterns = patterns('', (r'^archive/$', 'mysite.views.archive'), (r'^about/$', 'mysite.views.about'), ) Set two:: # main.py urlpatterns = patterns('', (r'^blog/', include('inner')), ) # inner.py urlpatterns = patterns('', (r'^archive/$', 'mysite.views.archive', {'blogid': 3}), (r'^about/$', 'mysite.views.about', {'blogid': 3}), ) Note that extra options will *always* be passed to *every* line in the included URLconf, regardless of whether the line's view actually accepts those options as valid. For this reason, this technique is only useful if you're certain that every view in the included URLconf accepts the extra options you're passing. Passing callable objects instead of strings =========================================== Some developers find it more natural to pass the actual Python function object rather than a string containing the path to its module. This alternative is supported -- you can pass any callable object as the view. For example, given this URLconf in "string" notation:: urlpatterns = patterns('', (r'^archive/$', 'mysite.views.archive'), (r'^about/$', 'mysite.views.about'), (r'^contact/$', 'mysite.views.contact'), ) You can accomplish the same thing by passing objects rather than strings. Just be sure to import the objects:: from mysite.views import archive, about, contact urlpatterns = patterns('', (r'^archive/$', archive), (r'^about/$', about), (r'^contact/$', contact), ) The following example is functionally identical. It's just a bit more compact because it imports the module that contains the views, rather than importing each view individually:: from mysite import views urlpatterns = patterns('', (r'^archive/$', views.archive), (r'^about/$', views.about), (r'^contact/$', views.contact), ) The style you use is up to you. Note that if you use this technique -- passing objects rather than strings -- the view prefix (as explained in "The view prefix" above) will have no effect. Note that :doc:`class based views` must be imported:: from mysite.views import ClassBasedView urlpatterns = patterns('', (r'^myview/$', ClassBasedView.as_view()), ) .. _naming-url-patterns: Naming URL patterns =================== It's fairly common to use the same view function in multiple URL patterns in your URLconf. For example, these two URL patterns both point to the ``archive`` view:: urlpatterns = patterns('', (r'^archive/(\d{4})/$', archive), (r'^archive-summary/(\d{4})/$', archive, {'summary': True}), ) This is completely valid, but it leads to problems when you try to do reverse URL matching (through the ``permalink()`` decorator or the :ttag:`url` template tag). Continuing this example, if you wanted to retrieve the URL for the ``archive`` view, Django's reverse URL matcher would get confused, because *two* URL patterns point at that view. To solve this problem, Django supports **named URL patterns**. That is, you can give a name to a URL pattern in order to distinguish it from other patterns using the same view and parameters. Then, you can use this name in reverse URL matching. Here's the above example, rewritten to use named URL patterns:: urlpatterns = patterns('', url(r'^archive/(\d{4})/$', archive, name="full-archive"), url(r'^archive-summary/(\d{4})/$', archive, {'summary': True}, "arch-summary"), ) With these names in place (``full-archive`` and ``arch-summary``), you can target each pattern individually by using its name: .. code-block:: html+django {% url 'arch-summary' 1945 %} {% url 'full-archive' 2007 %} Even though both URL patterns refer to the ``archive`` view here, using the ``name`` parameter to ``url()`` allows you to tell them apart in templates. The string used for the URL name can contain any characters you like. You are not restricted to valid Python names. .. note:: When you name your URL patterns, make sure you use names that are unlikely to clash with any other application's choice of names. If you call your URL pattern ``comment``, and another application does the same thing, there's no guarantee which URL will be inserted into your template when you use this name. Putting a prefix on your URL names, perhaps derived from the application name, will decrease the chances of collision. We recommend something like ``myapp-comment`` instead of ``comment``. .. _topics-http-reversing-url-namespaces: URL namespaces -------------- 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 ``foo:bar:whiz`` would look for a pattern named ``whiz`` in the namespace ``bar`` that is itself defined within the top-level namespace ``foo``. When given a namespaced URL (e.g. ``myapp:index``) to resolve, Django splits the fully qualified name into parts, and then tries the following lookup: 1. First, Django looks for a matching application namespace (in this example, ``myapp``). This will yield a list of instances of that application. 2. If there is a *current* application defined, Django finds and returns the URL resolver for that instance. The *current* application can be specified as an attribute on the template context - applications that expect to have multiple deployments should set the ``current_app`` attribute on any ``Context`` or ``RequestContext`` that is used to render a template. The current application can also be specified manually as an argument to the :func:`reverse()` function. 3. If there is no current application. Django looks for a default application instance. The default application instance is the instance that has an instance namespace matching the application namespace (in this example, an instance of the ``myapp`` called ``myapp``). 4. If there is no default application instance, Django will pick the last deployed instance of the application, whatever its instance name may be. 5. If the provided namespace doesn't match an application namespace in step 1, Django will attempt a direct lookup of the namespace as an 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. To show this resolution strategy in action, consider an example of two instances of ``myapp``: one called ``foo``, and one called ``bar``. ``myapp`` has a main index page with a URL named `index`. Using this setup, the following lookups are possible: * If one of the instances is current - say, if we were rendering a utility page in the instance ``bar`` - ``myapp:index`` will resolve to the index page of the instance ``bar``. * If there is no current instance - say, if we were rendering a page somewhere else on the site - ``myapp:index`` will resolve to the last registered instance of ``myapp``. Since there is no default instance, the last instance of ``myapp`` that is registered will be used. This could be ``foo`` or ``bar``, depending on the order they are introduced into the urlpatterns of the project. * ``foo:index`` will always resolve to the index page of the instance ``foo``. If there was also a default instance - i.e., an instance named `myapp` - the following would happen: * If one of the instances is current - say, if we were rendering a utility page in the instance ``bar`` - ``myapp:index`` will resolve to the index page of the instance ``bar``. * If there is no current instance - say, if we were rendering a page somewhere else on the site - ``myapp:index`` will resolve to the index page of the default instance. * ``foo:index`` will again resolve to the index page of the instance ``foo``. ``django.core.urlresolvers`` utility functions ============================================== .. currentmodule:: django.core.urlresolvers reverse() --------- If you need to use something similar to the :ttag:`url` template tag in your code, Django provides the following function (in the :mod:`django.core.urlresolvers` module): .. function:: reverse(viewname, [urlconf=None, args=None, kwargs=None, current_app=None]) ``viewname`` is either the function name (either a function reference, or the string version of the name, if you used that form in ``urlpatterns``) or the `URL pattern name`_. Normally, you won't need to worry about the ``urlconf`` parameter and will only pass in the positional and keyword arguments to use in the URL matching. For example:: from django.core.urlresolvers import reverse def myview(request): return HttpResponseRedirect(reverse('arch-summary', args=[1945])) .. _URL pattern name: `Naming URL patterns`_ The ``reverse()`` function can reverse a large variety of regular expression patterns for URLs, but not every possible one. The main restriction at the moment is that the pattern cannot contain alternative choices using the vertical bar (``"|"``) character. You can quite happily use such patterns for matching against incoming URLs and sending them off to views, but you cannot reverse such patterns. The ``current_app`` argument allows you to provide a hint to the resolver indicating the application to which the currently executing view belongs. This ``current_app`` argument is used as a hint to resolve application namespaces into URLs on specific application instances, according to the :ref:`namespaced URL resolution strategy `. You can use ``kwargs`` instead of ``args``. For example:: >>> reverse('admin:app_list', kwargs={'app_label': 'auth'}) '/admin/auth/' ``args`` and ``kwargs`` cannot be passed to ``reverse()`` at the same time. .. admonition:: Make sure your views are all correct. As part of working out which URL names map to which patterns, the ``reverse()`` function has to import all of your URLconf files and examine the name of each view. This involves importing each view function. If there are *any* errors whilst importing any of your view functions, it will cause ``reverse()`` to raise an error, even if that view function is not the one you are trying to reverse. Make sure that any views you reference in your URLconf files exist and can be imported correctly. Do not include lines that reference views you haven't written yet, because those views will not be importable. .. note:: The string returned by :meth:`~django.core.urlresolvers.reverse` is already :ref:`urlquoted `. For example:: >>> reverse('cities', args=[u'Orléans']) '.../Orl%C3%A9ans/' Applying further encoding (such as :meth:`~django.utils.http.urlquote` or ``urllib.quote``) to the output of :meth:`~django.core.urlresolvers.reverse` may produce undesirable results. reverse_lazy() -------------- .. versionadded:: 1.4 A lazily evaluated version of `reverse()`_. .. function:: reverse_lazy(viewname, [urlconf=None, args=None, kwargs=None, current_app=None]) It is useful for when you need to use a URL reversal before your project's URLConf is loaded. Some common cases where this function is necessary are: * providing a reversed URL as the ``url`` attribute of a generic class-based view. * providing a reversed URL to a decorator (such as the ``login_url`` argument for the :func:`django.contrib.auth.decorators.permission_required` decorator). * providing a reversed URL as a default value for a parameter in a function's signature. resolve() --------- The :func:`django.core.urlresolvers.resolve` function can be used for resolving URL paths to the corresponding view functions. It has the following signature: .. function:: resolve(path, urlconf=None) ``path`` is the URL path you want to resolve. As with :func:`~django.core.urlresolvers.reverse`, you don't need to worry about the ``urlconf`` parameter. The function returns a :class:`ResolverMatch` object that allows you to access various meta-data about the resolved URL. If the URL does not resolve, the function raises an :class:`~django.http.Http404` exception. .. class:: ResolverMatch .. attribute:: ResolverMatch.func The view function that would be used to serve the URL .. attribute:: ResolverMatch.args The arguments that would be passed to the view function, as parsed from the URL. .. attribute:: ResolverMatch.kwargs The keyword arguments that would be passed to the view function, as parsed from the URL. .. attribute:: ResolverMatch.url_name The name of the URL pattern that matches the URL. .. attribute:: ResolverMatch.app_name The application namespace for the URL pattern that matches the URL. .. attribute:: ResolverMatch.namespace The instance namespace for the URL pattern that matches the URL. .. attribute:: ResolverMatch.namespaces The list of individual namespace components in the full instance namespace for the URL pattern that matches the URL. i.e., if the namespace is ``foo:bar``, then namespaces will be ``['foo', 'bar']``. A :class:`ResolverMatch` object can then be interrogated to provide information about the URL pattern that matches a URL:: # Resolve a URL match = resolve('/some/path/') # Print the URL pattern that matches the URL print(match.url_name) A :class:`ResolverMatch` object can also be assigned to a triple:: func, args, kwargs = resolve('/some/path/') .. versionchanged:: 1.3 Triple-assignment exists for backwards-compatibility. Prior to Django 1.3, :func:`~django.core.urlresolvers.resolve` returned a triple containing (view function, arguments, keyword arguments); the :class:`ResolverMatch` object (as well as the namespace and pattern information it provides) is not available in earlier Django releases. One possible use of :func:`~django.core.urlresolvers.resolve` would be to test whether a view would raise a ``Http404`` error before redirecting to it:: from urlparse import urlparse from django.core.urlresolvers import resolve from django.http import HttpResponseRedirect, Http404 def myview(request): next = request.META.get('HTTP_REFERER', None) or '/' response = HttpResponseRedirect(next) # modify the request and response as required, e.g. change locale # and set corresponding locale cookie view, args, kwargs = resolve(urlparse(next)[2]) kwargs['request'] = request try: view(*args, **kwargs) except Http404: return HttpResponseRedirect('/') return response permalink() ----------- The :func:`django.db.models.permalink` decorator is useful for writing short methods that return a full URL path. For example, a model's ``get_absolute_url()`` method. See :func:`django.db.models.permalink` for more. get_script_prefix() ------------------- .. function:: get_script_prefix() Normally, you should always use :func:`~django.core.urlresolvers.reverse` or :func:`~django.db.models.permalink` to define URLs within your application. However, if your application constructs part of the URL hierarchy itself, you may occasionally need to generate URLs. In that case, you need to be able to find the base URL of the Django project within its Web server (normally, :func:`~django.core.urlresolvers.reverse` takes care of this for you). In that case, you can call ``get_script_prefix()``, which will return the script prefix portion of the URL for your Django project. If your Django project is at the root of its Web server, this is always ``"/"``.