django/docs/releases/4.1.txt

============================================
Django 4.1 release notes - UNDER DEVELOPMENT
============================================

*Expected August 2022*

Welcome to Django 4.1!

These release notes cover the :ref:`new features <whats-new-4.1>`, as well as
some :ref:`backwards incompatible changes <backwards-incompatible-4.1>` you'll
want to be aware of when upgrading from Django 4.0 or earlier. We've
:ref:`begun the deprecation process for some features
<deprecated-features-4.1>`.

See the :doc:`/howto/upgrade-version` guide if you're updating an existing
project.

Python compatibility
====================

Django 4.1 supports Python 3.8, 3.9, and 3.10. We **highly recommend** and only
officially support the latest release of each series.

.. _whats-new-4.1:

What's new in Django 4.1
========================

Asynchronous handlers for class-based views
-------------------------------------------

View subclasses may now define async HTTP method handlers::

    import asyncio
    from django.http import HttpResponse
    from django.views import View

    class AsyncView(View):
        async def get(self, request, *args, **kwargs):
            # Perform view logic using await.
            await asyncio.sleep(1)
            return HttpResponse("Hello async world!")

See :ref:`async-class-based-views` for more details.

Asynchronous ORM interface
--------------------------

``QuerySet`` now provides an asynchronous interface for all data access
operations. These are named as-per the existing synchronous operations but with
an ``a`` prefix, for example ``acreate()``, ``aget()``, and so on.

The new interface allows you to write asynchronous code without needing to wrap
ORM operations in ``sync_to_async()``::

    async for author in Author.objects.filter(name__startswith="A"):
        book = await author.books.afirst()

Note that, at this stage, the underlying database operations remain
synchronous, with contributions ongoing to push asynchronous support down into
the SQL compiler, and integrate asynchronous database drivers. The new
asynchronous queryset interface currently encapsulates the necessary
``sync_to_async()`` operations for you, and will allow your code to take
advantage of developments in the ORM's asynchronous support as it evolves.

See :ref:`async-queries` for details and limitations.

Validation of Constraints
-------------------------

:class:`Check <django.db.models.CheckConstraint>`,
:class:`unique <django.db.models.UniqueConstraint>`, and :class:`exclusion
<django.contrib.postgres.constraints.ExclusionConstraint>` constraints defined
in the :attr:`Meta.constraints <django.db.models.Options.constraints>` option
are now checked during :ref:`model validation <validating-objects>`.

.. _csrf-cookie-masked-usage:

``CSRF_COOKIE_MASKED`` setting
------------------------------

The new :setting:`CSRF_COOKIE_MASKED` transitional setting allows specifying
whether to mask the CSRF cookie.

:class:`~django.middleware.csrf.CsrfViewMiddleware` no longer masks the CSRF
cookie like it does the CSRF token in the DOM. If you are upgrading multiple
instances of the same project to Django 4.1, you should set
:setting:`CSRF_COOKIE_MASKED` to ``True`` during the transition, in
order to allow compatibility with the older versions of Django. Once the
transition to 4.1 is complete you can stop overriding
:setting:`CSRF_COOKIE_MASKED`.

This setting is deprecated as of this release and will be removed in Django
5.0.

Minor features
--------------

:mod:`django.contrib.admin`
~~~~~~~~~~~~~~~~~~~~~~~~~~~

* The admin :ref:`dark mode CSS variables <admin-theming>` are now applied in a
  separate stylesheet and template block.

* :ref:`modeladmin-list-filters` providing custom ``FieldListFilter``
  subclasses can now control the query string value separator when filtering
  for multiple values using the ``__in`` lookup.

* The admin :meth:`history view <django.contrib.admin.ModelAdmin.history_view>`
  is now paginated.

* Related widget wrappers now have a link to object's change form.

* The :meth:`.AdminSite.get_app_list` method now allows changing the order of
  apps and models on the admin index page.

:mod:`django.contrib.admindocs`
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

* ...

:mod:`django.contrib.auth`
~~~~~~~~~~~~~~~~~~~~~~~~~~

* The default iteration count for the PBKDF2 password hasher is increased from
  320,000 to 390,000.

* The :meth:`.RemoteUserBackend.configure_user` method now allows synchronizing
  user attributes with attributes in a remote system such as an LDAP directory.

:mod:`django.contrib.contenttypes`
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

* ...

:mod:`django.contrib.gis`
~~~~~~~~~~~~~~~~~~~~~~~~~

* The new :meth:`.GEOSGeometry.make_valid()` method allows converting invalid
  geometries to valid ones.

* The new ``clone`` argument for :meth:`.GEOSGeometry.normalize` allows
  creating a normalized clone of the geometry.

:mod:`django.contrib.messages`
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

* ...

:mod:`django.contrib.postgres`
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

* The new :class:`BitXor() <django.contrib.postgres.aggregates.BitXor>`
  aggregate function returns an ``int`` of the bitwise ``XOR`` of all non-null
  input values.

* :class:`~django.contrib.postgres.indexes.SpGistIndex` now supports covering
  indexes on PostgreSQL 14+.

* :class:`~django.contrib.postgres.constraints.ExclusionConstraint` now
  supports covering exclusion constraints using SP-GiST indexes on PostgreSQL
  14+.

* The new ``default_bounds`` attribute of :attr:`DateTimeRangeField
  <django.contrib.postgres.fields.DateTimeRangeField.default_bounds>` and
  :attr:`DecimalRangeField
  <django.contrib.postgres.fields.DecimalRangeField.default_bounds>` allows
  specifying bounds for list and tuple inputs.

* :class:`~django.contrib.postgres.constraints.ExclusionConstraint` now allows
  specifying operator classes with the
  :class:`OpClass() <django.contrib.postgres.indexes.OpClass>` expression.

:mod:`django.contrib.redirects`
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

* ...

:mod:`django.contrib.sessions`
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

* ...

:mod:`django.contrib.sitemaps`
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

* The default sitemap index template ``<sitemapindex>`` now includes the
  ``<lastmod>`` timestamp where available, through the new
  :meth:`~django.contrib.sitemaps.Sitemap.get_latest_lastmod` method. Custom
  sitemap index templates should be updated for the adjusted :ref:`context
  variables <sitemap-index-context-variables>`.

:mod:`django.contrib.sites`
~~~~~~~~~~~~~~~~~~~~~~~~~~~

* ...

:mod:`django.contrib.staticfiles`
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

* :class:`~django.contrib.staticfiles.storage.ManifestStaticFilesStorage` now
  replaces paths to CSS source map references with their hashed counterparts.

:mod:`django.contrib.syndication`
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

* ...

Cache
~~~~~

* ...

CSRF
~~~~

* ...

Database backends
~~~~~~~~~~~~~~~~~

* Third-party database backends can now specify the minimum required version of
  the database using the ``DatabaseFeatures.minimum_database_version``
  attribute which is a tuple (e.g. ``(10, 0)`` means "10.0"). If a minimum
  version is specified, backends must also implement
  ``DatabaseWrapper.get_database_version()``, which returns a tuple of the
  current database version. The backend's
  ``DatabaseWrapper.init_connection_state()`` method must call ``super()`` in
  order for the check to run.

Decorators
~~~~~~~~~~

* ...

Email
~~~~~

* ...

Error Reporting
~~~~~~~~~~~~~~~

* ...

File Storage
~~~~~~~~~~~~

* ...

File Uploads
~~~~~~~~~~~~

* ...

Forms
~~~~~

* The default template used to render forms when cast to a string, e.g. in
  templates as ``{{ form }}``, is now configurable at the project-level by
  setting :attr:`~django.forms.renderers.BaseRenderer.form_template_name` on
  the class provided for :setting:`FORM_RENDERER`.

  :attr:`.Form.template_name` is now a property deferring to the renderer, but
  may be overridden with a string value to specify the template name per-form
  class.

  Similarly, the default template used to render formsets can be specified via
  the matching
  :attr:`~django.forms.renderers.BaseRenderer.formset_template_name` renderer
  attribute.

* The new ``div.html`` form template, referencing
  :attr:`.Form.template_name_div` attribute, and matching :meth:`.Form.as_div`
  method, render forms using HTML ``<div>`` elements.

  This new output style is recommended over the existing
  :meth:`~.Form.as_table`, :meth:`~.Form.as_p` and :meth:`~.Form.as_ul` styles,
  as the template implements ``<fieldset>`` and ``<legend>`` to group related
  inputs and is easier for screen reader users to navigate.

* The new :meth:`~django.forms.BoundField.legend_tag` allows rendering field
  labels in ``<legend>`` tags via the new ``tag`` argument of
  :meth:`~django.forms.BoundField.label_tag`.

* The new ``edit_only`` argument for :func:`.modelformset_factory` and
  :func:`.inlineformset_factory` allows preventing new objects creation.

* The ``js`` and ``css`` class attributes of :doc:`Media </topics/forms/media>`
  now allow using hashable objects, not only path strings, as long as those
  objects implement the ``__html__()`` method (typically when decorated with
  the :func:`~django.utils.html.html_safe` decorator).

* The new :attr:`.BoundField.use_fieldset` and :attr:`.Widget.use_fieldset`
  attributes help to identify widgets where its inputs should be grouped in a
  ``<fieldset>`` with a ``<legend>``.

* The :ref:`formsets-error-messages` argument for
  :class:`~django.forms.formsets.BaseFormSet` now allows customizing
  error messages for invalid number of forms by passing ``'too_few_forms'``
  and ``'too_many_forms'`` keys.

* :class:`~django.forms.IntegerField`, :class:`~django.forms.FloatField`, and
  :class:`~django.forms.DecimalField` now optionally accept a ``step_size``
  argument. This is used to set the ``step`` HTML attribute, and is validated
  on form submission.

Generic Views
~~~~~~~~~~~~~

* ...

Internationalization
~~~~~~~~~~~~~~~~~~~~

* The :func:`~django.conf.urls.i18n.i18n_patterns` function now supports
  languages with both scripts and regions.

Logging
~~~~~~~

* ...

Management Commands
~~~~~~~~~~~~~~~~~~~

* :option:`makemigrations --no-input` now logs default answers and reasons why
  migrations cannot be created.

* The new :option:`makemigrations --scriptable` option diverts log output and
  input prompts to ``stderr``, writing only paths of generated migration files
  to ``stdout``.

* The new :option:`migrate --prune` option allows deleting nonexistent
  migrations from the ``django_migrations`` table.

* Python files created by :djadmin:`startproject`, :djadmin:`startapp`,
  :djadmin:`optimizemigration`, :djadmin:`makemigrations`, and
  :djadmin:`squashmigrations` are now formatted using the ``black`` command if
  it is present on your ``PATH``.

* The new :djadmin:`optimizemigration` command allows optimizing operations for
  a migration.

Migrations
~~~~~~~~~~

* The new :class:`~django.db.migrations.operations.RenameIndex` operation
  allows renaming indexes defined in the
  :attr:`Meta.indexes <django.db.models.Options.indexes>` or
  :attr:`~django.db.models.Options.index_together` options.

Models
~~~~~~

* The ``order_by`` argument of the
  :class:`~django.db.models.expressions.Window` expression now accepts string
  references to fields and transforms.

* The new :setting:`CONN_HEALTH_CHECKS` setting allows enabling health checks
  for :ref:`persistent database connections <persistent-database-connections>`
  in order to reduce the number of failed requests, e.g. after database server
  restart.

* :meth:`.QuerySet.bulk_create` now supports updating fields when a row
  insertion fails uniqueness constraints. This is supported on MariaDB, MySQL,
  PostgreSQL, and SQLite 3.24+.

* :meth:`.QuerySet.iterator` now supports prefetching related objects as long
  as the ``chunk_size`` argument is provided. In older versions, no prefetching
  was done.

* :class:`~django.db.models.Q` objects and querysets can now be combined using
  ``^`` as the exclusive or (``XOR``) operator. ``XOR`` is natively supported
  on MariaDB and MySQL. For databases that do not support ``XOR``, the query
  will be converted to an equivalent using ``AND``, ``OR``, and ``NOT``.

* The new :ref:`Field.non_db_attrs <custom-field-non_db_attrs>` attribute
  allows customizing attributes of fields that don't affect a column
  definition.

* On PostgreSQL, ``AutoField``, ``BigAutoField``, and ``SmallAutoField`` are
  now created as identity columns rather than serial columns with sequences.

Requests and Responses
~~~~~~~~~~~~~~~~~~~~~~

* :meth:`.HttpResponse.set_cookie` now supports :class:`~datetime.timedelta`
  objects for the ``max_age`` argument.

Security
~~~~~~~~

* The new :setting:`SECRET_KEY_FALLBACKS` setting allows providing a list of
  values for secret key rotation.

* The :setting:`SECURE_PROXY_SSL_HEADER` setting now supports a comma-separated
  list of protocols in the header value.

Serialization
~~~~~~~~~~~~~

* ...

Signals
~~~~~~~

* The :data:`~django.db.models.signals.pre_delete` and
  :data:`~django.db.models.signals.post_delete` signals now dispatch the
  ``origin`` of the deletion.

.. _templates-4.1:

Templates
~~~~~~~~~

* :tfilter:`json_script` template filter now allows wrapping in a ``<script>``
  tag without the HTML ``id`` attribute.

* The :class:`cached template loader <django.template.loaders.cached.Loader>`
  is now enabled in development, when :setting:`DEBUG` is ``True``, and
  :setting:`OPTIONS['loaders'] <TEMPLATES-OPTIONS>` isn't specified. You may
  specify ``OPTIONS['loaders']`` to override this, if necessary.

Tests
~~~~~

* The :class:`.DiscoverRunner` now supports running tests in parallel on
  macOS, Windows, and any other systems where the default
  :mod:`multiprocessing` start method is ``spawn``.

* A nested atomic block marked as durable in :class:`django.test.TestCase` now
  raises a ``RuntimeError``, the same as outside of tests.

* :meth:`.SimpleTestCase.assertFormError` and
  :meth:`~.SimpleTestCase.assertFormsetError` now support passing a
  form/formset object directly.

URLs
~~~~

* The new :attr:`.ResolverMatch.captured_kwargs` attribute stores the captured
  keyword arguments, as parsed from the URL.

* The new :attr:`.ResolverMatch.extra_kwargs` attribute stores the additional
  keyword arguments passed to the view function.

Utilities
~~~~~~~~~

* ``SimpleLazyObject`` now supports addition operations.

* :func:`~django.utils.safestring.mark_safe` now preserves lazy objects.

Validators
~~~~~~~~~~

* The new :class:`~django.core.validators.StepValueValidator` checks if a value
  is an integral multiple of a given step size. This new validator is used for
  the new ``step_size`` argument added to form fields representing numeric
  values.

.. _backwards-incompatible-4.1:

Backwards incompatible changes in 4.1
=====================================

Database backend API
--------------------

This section describes changes that may be needed in third-party database
backends.

* ``BaseDatabaseFeatures.has_case_insensitive_like`` is changed from ``True``
  to ``False`` to reflect the behavior of most databases.

* ``DatabaseIntrospection.get_key_columns()`` is removed. Use
  ``DatabaseIntrospection.get_relations()`` instead.

* ``DatabaseOperations.ignore_conflicts_suffix_sql()`` method is replaced by
  ``DatabaseOperations.on_conflict_suffix_sql()`` that accepts the ``fields``,
  ``on_conflict``, ``update_fields``, and ``unique_fields`` arguments.

* The ``ignore_conflicts`` argument of the
  ``DatabaseOperations.insert_statement()`` method is replaced by
  ``on_conflict`` that accepts ``django.db.models.constants.OnConflict``.

:mod:`django.contrib.gis`
-------------------------

* Support for GDAL 2.1 is removed.

* Support for PostGIS 2.4 is removed.

Dropped support for PostgreSQL 10
---------------------------------

Upstream support for PostgreSQL 10 ends in November 2022. Django 4.1 supports
PostgreSQL 11 and higher.

Dropped support for MariaDB 10.2
--------------------------------

Upstream support for MariaDB 10.2 ends in May 2022. Django 4.1 supports MariaDB
10.3 and higher.

Admin changelist searches spanning multi-valued relationships changes
---------------------------------------------------------------------

Admin changelist searches using multiple search terms are now applied in a
single call to ``filter()``, rather than in sequential ``filter()`` calls.

For multi-valued relationships, this means that rows from the related model
must match all terms rather than any term. For example, if ``search_fields``
is set to ``['child__name', 'child__age']``, and a user searches for
``'Jamal 17'``, parent rows will be returned only if there is a relationship to
some 17-year-old child named Jamal, rather than also returning parents who
merely have a younger or older child named Jamal in addition to some other
17-year-old.

See the :ref:`spanning-multi-valued-relationships` topic for more discussion of
this difference. In Django 4.0 and earlier,
:meth:`~django.contrib.admin.ModelAdmin.get_search_results` followed the
second example query, but this undocumented behavior led to queries with
excessive joins.

Reverse foreign key changes for unsaved model instances
-------------------------------------------------------

In order to unify the behavior with many-to-many relations for unsaved model
instances, a reverse foreign key now raises ``ValueError`` when calling
:class:`related managers <django.db.models.fields.related.RelatedManager>` for
unsaved objects.

Miscellaneous
-------------

* Related managers for :class:`~django.db.models.ForeignKey`,
  :class:`~django.db.models.ManyToManyField`, and
  :class:`~django.contrib.contenttypes.fields.GenericRelation` are now cached
  on the :class:`~django.db.models.Model` instance to which they belong.

* The Django test runner now returns a non-zero error code for unexpected
  successes from tests marked with :py:func:`unittest.expectedFailure`.

* :class:`~django.middleware.csrf.CsrfViewMiddleware` no longer masks the CSRF
  cookie like it does the CSRF token in the DOM.

* :class:`~django.middleware.csrf.CsrfViewMiddleware` now uses
  ``request.META['CSRF_COOKIE']`` for storing the unmasked CSRF secret rather
  than a masked version. This is an undocumented, private API.

* The :attr:`.ModelAdmin.actions` and
  :attr:`~django.contrib.admin.ModelAdmin.inlines` attributes now default to an
  empty tuple rather than an empty list to discourage unintended mutation.

* The ``type="text/css"`` attribute is no longer included in ``<link>`` tags
  for CSS :doc:`form media </topics/forms/media>`.

* ``formset:added`` and ``formset:removed`` JavaScript events are now pure
  JavaScript events and don't depend on jQuery. See
  :ref:`admin-javascript-inline-form-events` for more details on the change.

* The ``exc_info`` argument of the undocumented
  ``django.utils.log.log_response()`` function is replaced by ``exception``.

* The ``size`` argument of the undocumented
  ``django.views.static.was_modified_since()`` function is removed.

* The admin log out UI now uses ``POST`` requests.

* The undocumented ``InlineAdminFormSet.non_form_errors`` property is replaced
  by the ``non_form_errors()`` method. This is consistent with ``BaseFormSet``.

* As per :ref:`above<templates-4.1>`, the cached template loader is now
  enabled in development. You may specify ``OPTIONS['loaders']`` to override
  this, if necessary.

* The undocumented ``django.contrib.auth.views.SuccessURLAllowedHostsMixin``
  mixin is replaced by ``RedirectURLMixin``.

* :class:`~django.db.models.BaseConstraint` subclasses must implement
  :meth:`~django.db.models.BaseConstraint.validate` method to allow those
  constraints to be used for validation.

.. _deprecated-features-4.1:

Features deprecated in 4.1
==========================

Log out via GET
---------------

Logging out via ``GET`` requests to the :py:class:`built-in logout view
<django.contrib.auth.views.LogoutView>` is deprecated. Use ``POST`` requests
instead.

If you want to retain the user experience of an HTML link, you can use a form
that is styled to appear as a link:

.. code-block:: html

  <form id="logout-form" method="post" action="{% url 'admin:logout' %}">
    {% csrf_token %}
    <button type="submit">{% translate "Log out" %}</button>
  </form>

.. code-block:: css

  #logout-form {
    display: inline;
  }
  #logout-form button {
    background: none;
    border: none;
    cursor: pointer;
    padding: 0;
    text-decoration: underline;
  }

Miscellaneous
-------------

* The context for sitemap index templates of a flat list of URLs is deprecated.
  Custom sitemap index templates should be updated for the adjusted
  :ref:`context variables <sitemap-index-context-variables>`, expecting a list
  of objects with ``location`` and optional ``lastmod`` attributes.

* ``CSRF_COOKIE_MASKED`` transitional setting is deprecated.

* The ``name`` argument of :func:`django.utils.functional.cached_property` is
  deprecated as it's unnecessary as of Python 3.6.

* The ``opclasses`` argument of
  ``django.contrib.postgres.constraints.ExclusionConstraint`` is deprecated in
  favor of using :class:`OpClass() <django.contrib.postgres.indexes.OpClass>`
  in :attr:`.ExclusionConstraint.expressions`. To use it, you need to add
  ``'django.contrib.postgres'`` in your :setting:`INSTALLED_APPS`.

  After making this change, :djadmin:`makemigrations` will generate a new
  migration with two operations: ``RemoveConstraint`` and ``AddConstraint``.
  Since this change has no effect on the database schema,
  the :class:`~django.db.migrations.operations.SeparateDatabaseAndState`
  operation can be used to only update the migration state without running any
  SQL. Move the generated operations into the ``state_operations`` argument of
  :class:`~django.db.migrations.operations.SeparateDatabaseAndState`. For
  example::

    class Migration(migrations.Migration):
        ...

        operations = [
            migrations.SeparateDatabaseAndState(
                database_operations=[],
                state_operations=[
                    migrations.RemoveConstraint(
                        ...
                    ),
                    migrations.AddConstraint(
                        ...
                    ),
                ],
            ),
        ]

* The undocumented ability to pass ``errors=None`` to
  :meth:`.SimpleTestCase.assertFormError` and
  :meth:`~.SimpleTestCase.assertFormsetError` is deprecated. Use ``errors=[]``
  instead.

* ``django.contrib.sessions.serializers.PickleSerializer`` is deprecated due to
  the risk of remote code execution.

* The usage of ``QuerySet.iterator()`` on a queryset that prefetches related
  objects without providing the ``chunk_size`` argument is deprecated. In older
  versions, no prefetching was done. Providing a value for ``chunk_size``
  signifies that the additional query per chunk needed to prefetch is desired.

* Passing unsaved model instances to related filters is deprecated. In Django
  5.0, the exception will be raised.

* ``created=True`` is added to the signature of
  :meth:`.RemoteUserBackend.configure_user`. Support  for ``RemoteUserBackend``
  subclasses that do not accept this argument is deprecated.

* The :data:`django.utils.timezone.utc` alias to :attr:`datetime.timezone.utc`
  is deprecated. Use :attr:`datetime.timezone.utc` directly.

* Passing a response object and a form/formset name to
  ``SimpleTestCase.assertFormError()`` and ``assertFormsetError()`` is
  deprecated. Use::

    assertFormError(response.context['form_name'], …)
    assertFormsetError(response.context['formset_name'], …)

  or pass the form/formset object directly instead.

* The undocumented ``django.contrib.gis.admin.OpenLayersWidget`` is deprecated.

* ``django.contrib.auth.hashers.CryptPasswordHasher`` is deprecated.

* The ability to pass ``nulls_first=False`` or ``nulls_last=False`` to
  ``Expression.asc()`` and ``Expression.desc()`` methods, and the ``OrderBy``
  expression is deprecated. Use ``None`` instead.

Features removed in 4.1
=======================

These features have reached the end of their deprecation cycle and are removed
in Django 4.1.

See :ref:`deprecated-features-3.2` for details on these changes, including how
to remove usage of these features.

* Support for assigning objects which don't support creating deep copies with
  ``copy.deepcopy()`` to class attributes in ``TestCase.setUpTestData()`` is
  removed.

* Support for using a boolean value in
  :attr:`.BaseCommand.requires_system_checks` is removed.

* The ``whitelist`` argument and ``domain_whitelist`` attribute of
  ``django.core.validators.EmailValidator`` are removed.

* The ``default_app_config`` application configuration variable is removed.

* ``TransactionTestCase.assertQuerysetEqual()`` no longer calls ``repr()`` on a
  queryset when compared to string values.

* The ``django.core.cache.backends.memcached.MemcachedCache`` backend is
  removed.

* Support for the pre-Django 3.2 format of messages used by
  ``django.contrib.messages.storage.cookie.CookieStorage`` is removed.