=================================
``django.urls`` utility functions
=================================

.. module:: django.urls

``reverse()``
=============

The ``reverse()`` function can be used to return an absolute path reference
for a given view and optional parameters, similar to the :ttag:`url` tag:

.. function:: reverse(viewname, urlconf=None, args=None, kwargs=None, current_app=None, *, query=None, fragment=None)

``viewname`` can be a :ref:`URL pattern name <naming-url-patterns>` or the
callable view object used in the URLconf. For example, given the following
``url``::

    from news import views

    path("archive/", views.archive, name="news-archive")

you can use any of the following to reverse the URL::

    # using the named URL
    reverse("news-archive")

    # passing a callable object
    # (This is discouraged because you can't reverse namespaced views this way.)
    from news import views

    reverse(views.archive)

If the URL accepts arguments, you may pass them in ``args``. For example::

    from django.urls import reverse


    def myview(request):
        return HttpResponseRedirect(reverse("arch-summary", args=[1945]))

You can also pass ``kwargs`` instead of ``args``. For example:

.. code-block:: pycon

    >>> reverse("admin:app_list", kwargs={"app_label": "auth"})
    '/admin/auth/'

``args`` and ``kwargs`` cannot be passed to ``reverse()`` at the same time.

If no match can be made, ``reverse()`` raises a
:class:`~django.urls.NoReverseMatch` exception.

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

The ``urlconf`` argument is the URLconf module containing the URL patterns to
use for reversing. By default, the root URLconf for the current thread is used.

The ``query`` keyword argument specifies parameters to be added to the returned
URL. It can accept an instance of :class:`~django.http.QueryDict` (such as
``request.GET``) or any value compatible with :func:`urllib.parse.urlencode`.
The encoded query string is appended to the resolved URL, prefixed by a ``?``.

The ``fragment`` keyword argument specifies a fragment identifier to be
appended to the returned URL (that is, after the path and query string,
preceded by a ``#``).

For example:

.. code-block:: pycon

   >>> from django.urls import reverse
   >>> reverse("admin:index", query={"q": "biscuits", "page": 2}, fragment="results")
   '/admin/?q=biscuits&page=2#results'
   >>> reverse("admin:index", query=[("color", "blue"), ("color", 1), ("none", None)])
   '/admin/?color=blue&color=1&none=None'
   >>> reverse("admin:index", query={"has empty spaces": "also has empty spaces!"})
   '/admin/?has+empty+spaces=also+has+empty+spaces%21'
   >>> reverse("admin:index", fragment="no encoding is done")
   '/admin/#no encoding is done'

.. note::

    The string returned by ``reverse()`` is already
    :ref:`urlquoted <uri-and-iri-handling>`. For example:

    .. code-block:: pycon

        >>> reverse("cities", args=["Orléans"])
        '.../Orl%C3%A9ans/'

    Applying further encoding (such as :func:`urllib.parse.quote`) to the
    output of ``reverse()`` may produce undesirable results.

.. admonition:: Reversing class-based views by view object

    The view object can also be the result of calling
    :meth:`~django.views.generic.base.View.as_view` if the same view object is
    used in the URLConf. Following the original example, the view object could
    be defined as:

    .. code-block:: python
       :caption: ``news/views.py``

        from django.views import View


        class ArchiveView(View): ...


        archive = ArchiveView.as_view()

    However, remember that namespaced views cannot be reversed by view object.

``reverse_lazy()``
==================

A lazily evaluated version of `reverse()`_.

.. function:: reverse_lazy(viewname, urlconf=None, args=None, kwargs=None, current_app=None, *, query=None, fragment=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 ``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.urls.reverse`, you don't need to worry about the ``urlconf``
parameter. The function returns a :class:`ResolverMatch` object that allows you
to access various metadata about the resolved URL.

If the URL does not resolve, the function raises a
:exc:`~django.urls.Resolver404` exception (a subclass of
:class:`~django.http.Http404`) .

.. 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

        All keyword arguments that would be passed to the view function, i.e.
        :attr:`~ResolverMatch.captured_kwargs` and
        :attr:`~ResolverMatch.extra_kwargs`.

    .. attribute:: ResolverMatch.captured_kwargs

        The captured keyword arguments that would be passed to the view
        function, as parsed from the URL.

    .. attribute:: ResolverMatch.extra_kwargs

        The additional keyword arguments that would be passed to the view
        function.

    .. attribute:: ResolverMatch.url_name

        The name of the URL pattern that matches the URL.

    .. attribute:: ResolverMatch.route

        The route of the matching URL pattern.

        For example, if ``path('users/<id>/', ...)`` is the matching pattern,
        ``route`` will contain ``'users/<id>/'``.

    .. attribute:: ResolverMatch.tried

        The list of URL patterns tried before the URL either matched one or
        exhausted available patterns.

    .. attribute:: ResolverMatch.app_name

        The application namespace for the URL pattern that matches the
        URL.

    .. attribute:: ResolverMatch.app_names

        The list of individual namespace components in the full
        application namespace for the URL pattern that matches the URL.
        For example, if the ``app_name`` is ``'foo:bar'``, then ``app_names``
        will be ``['foo', 'bar']``.

    .. 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']``.

    .. attribute:: ResolverMatch.view_name

        The name of the view that matches the URL, including the namespace if
        there is one.

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/")

One possible use of :func:`~django.urls.resolve` would be to test whether a
view would raise a ``Http404`` error before redirecting to it::

    from urllib.parse import urlsplit
    from django.urls import resolve
    from django.http import Http404, HttpResponseRedirect


    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(urlsplit(next).path)
        kwargs["request"] = request
        try:
            view(*args, **kwargs)
        except Http404:
            return HttpResponseRedirect("/")
        return response

``get_script_prefix()``
=======================

.. function:: get_script_prefix()

Normally, you should always use :func:`~django.urls.reverse` 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.urls.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 ``"/"``.

.. warning::

    This function **cannot** be used outside of the request-response cycle
    since it relies on values initialized during that cycle.
