Update django to 3.2

[pyup-bot]

This PR updates Django from 2.1.7 to 3.2.

Changelog

3.2

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

*April 6, 2021*

Welcome to Django 3.2!

These release notes cover the :ref:`new features <whats-new-3.2>`, as well as
some :ref:`backwards incompatible changes <backwards-incompatible-3.2>` you'll
want to be aware of when upgrading from Django 3.1 or earlier. We've
:ref:`begun the deprecation process for some features
<deprecated-features-3.2>`.

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

Django 3.2 is designated as a :term:`long-term support release
<Long-term support release>`. It will receive security updates for at least
three years after its release. Support for the previous LTS, Django 2.2, will
end in April 2022.

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

Django 3.2 supports Python 3.6, 3.7, 3.8, and 3.9. We **highly recommend** and
only officially support the latest release of each series.

.. _whats-new-3.2:

What's new in Django 3.2
========================

Automatic :class:`~django.apps.AppConfig` discovery
---------------------------------------------------

Most pluggable applications define an :class:`~django.apps.AppConfig` subclass
in an ``apps.py`` submodule. Many define a ``default_app_config`` variable
pointing to this class in their ``__init__.py``.

When the ``apps.py`` submodule exists and defines a single
:class:`~django.apps.AppConfig` subclass, Django now uses that configuration
automatically, so you can remove ``default_app_config``.

``default_app_config`` made it possible to declare only the application's path
in :setting:`INSTALLED_APPS` (e.g. ``'django.contrib.admin'``) rather than the
app config's path (e.g. ``'django.contrib.admin.apps.AdminConfig'``). It was
introduced for backwards-compatibility with the former style, with the intent
to switch the ecosystem to the latter, but the switch didn't happen.

With automatic ``AppConfig`` discovery, ``default_app_config`` is no longer
needed. As a consequence, it's deprecated.

See :ref:`configuring-applications-ref` for full details.

Customizing type of auto-created primary keys
---------------------------------------------

When defining a model, if no field in a model is defined with
:attr:`primary_key=True <django.db.models.Field.primary_key>` an implicit
primary key is added. The type of this implicit primary key can now be
controlled via the :setting:`DEFAULT_AUTO_FIELD` setting and
:attr:`AppConfig.default_auto_field <django.apps.AppConfig.default_auto_field>`
attribute. No more needing to override primary keys in all models.

Maintaining the historical behavior, the default value for
:setting:`DEFAULT_AUTO_FIELD` is :class:`~django.db.models.AutoField`. Starting
with 3.2 new projects are generated with :setting:`DEFAULT_AUTO_FIELD` set to
:class:`~django.db.models.BigAutoField`. Also, new apps are generated with
:attr:`AppConfig.default_auto_field <django.apps.AppConfig.default_auto_field>`
set to :class:`~django.db.models.BigAutoField`. In a future Django release the
default value of :setting:`DEFAULT_AUTO_FIELD` will be changed to
:class:`~django.db.models.BigAutoField`.

To avoid unwanted migrations in the future, either explicitly set
:setting:`DEFAULT_AUTO_FIELD` to :class:`~django.db.models.AutoField`::

 DEFAULT_AUTO_FIELD = 'django.db.models.AutoField'

or configure it on a per-app basis::

 from django.apps import AppConfig

 class MyAppConfig(AppConfig):
     default_auto_field = 'django.db.models.AutoField'
     name = 'my_app'

or on a per-model basis::

 from django.db import models

 class MyModel(models.Model):
     id = models.AutoField(primary_key=True)

In anticipation of the changing default, a system check will provide a warning
if you do not have an explicit setting for :setting:`DEFAULT_AUTO_FIELD`.

.. _new_functional_indexes:

Functional indexes
------------------

The new :attr:`*expressions <django.db.models.Index.expressions>` positional
argument of :class:`Index() <django.db.models.Index>` enables creating
functional indexes on expressions and database functions. For example::

 from django.db import models
 from django.db.models import F, Index, Value
 from django.db.models.functions import Lower, Upper


 class MyModel(models.Model):
     first_name = models.CharField(max_length=255)
     last_name = models.CharField(max_length=255)
     height = models.IntegerField()
     weight = models.IntegerField()

     class Meta:
         indexes = [
             Index(
                 Lower('first_name'),
                 Upper('last_name').desc(),
                 name='first_last_name_idx',
             ),
             Index(
                 F('height') / (F('weight') + Value(5)),
                 name='calc_idx',
             ),
         ]

Functional indexes are added to models using the
:attr:`Meta.indexes <django.db.models.Options.indexes>` option.

``pymemcache`` support
----------------------

The new ``django.core.cache.backends.memcached.PyMemcacheCache`` cache backend
allows using the pymemcache_ library for memcached. ``pymemcache`` 3.4.0 or
higher is required. For more details, see the :doc:`documentation on caching in
Django </topics/cache>`.

.. _pymemcache: https://pypi.org/project/pymemcache/

New decorators for the admin site
---------------------------------

The new :func:`~django.contrib.admin.display` decorator allows for easily
adding options to custom display functions that can be used with
:attr:`~django.contrib.admin.ModelAdmin.list_display` or
:attr:`~django.contrib.admin.ModelAdmin.readonly_fields`.

Likewise, the new :func:`~django.contrib.admin.action` decorator allows for
easily adding options to action functions that can be used with
:attr:`~django.contrib.admin.ModelAdmin.actions`.

Using the ``display`` decorator has the advantage that it is now
possible to use the ``property`` decorator when needing to specify attributes
on the custom method. Prior to this it was necessary to use the ``property()``
function instead after assigning the required attributes to the method.

Using decorators has the advantage that these options are more discoverable as
they can be suggested by completion utilities in code editors. They are merely
a convenience and still set the same attributes on the functions under the
hood.

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

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

* :attr:`.ModelAdmin.search_fields` now allows searching against quoted
phrases with spaces.

* Read-only related fields are now rendered as navigable links if target
models are registered in the admin.

* The admin now supports theming, and includes a dark theme that is enabled
according to browser settings. See :ref:`admin-theming` for more details.

* :attr:`.ModelAdmin.autocomplete_fields` now respects
:attr:`ForeignKey.to_field <django.db.models.ForeignKey.to_field>` and
:attr:`ForeignKey.limit_choices_to
<django.db.models.ForeignKey.limit_choices_to>` when searching a related
model.

* The admin now installs a final catch-all view that redirects unauthenticated
users to the login page, regardless of whether the URL is otherwise valid.
This protects against a potential model enumeration privacy issue.

Although not recommended, you may set the new
:attr:`.AdminSite.final_catch_all_view` to ``False`` to disable the
catch-all view.

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

* The default iteration count for the PBKDF2 password hasher is increased from
216,000 to 260,000.

* The default variant for the Argon2 password hasher is changed to Argon2id.
``memory_cost`` and ``parallelism`` are increased to 102,400 and 8
respectively to match the ``argon2-cffi`` defaults.

Increasing the ``memory_cost`` pushes the required memory from 512 KB to 100
MB. This is still rather conservative but can lead to problems in memory
constrained environments. If this is the case, the existing hasher can be
subclassed to override the defaults.

* The default salt entropy for the Argon2, MD5, PBKDF2, SHA-1 password hashers
is increased from 71 to 128 bits.

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

* The new ``absolute_max`` argument for
:func:`~django.contrib.contenttypes.forms.generic_inlineformset_factory`
allows customizing the maximum number of forms that can be instantiated when
supplying ``POST`` data. See :ref:`formsets-absolute-max` for more details.

* The new ``can_delete_extra`` argument for
:func:`~django.contrib.contenttypes.forms.generic_inlineformset_factory`
allows removal of the option to delete extra forms. See
:attr:`~.BaseFormSet.can_delete_extra` for more information.

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

* The :meth:`.GDALRaster.transform` method now supports
:class:`~django.contrib.gis.gdal.SpatialReference`.

* The :class:`~django.contrib.gis.gdal.DataSource` class now supports
:class:`pathlib.Path`.

* The :class:`~django.contrib.gis.utils.LayerMapping` class now supports
:class:`pathlib.Path`.

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

* The new :attr:`.ExclusionConstraint.include` attribute allows creating
covering exclusion constraints on PostgreSQL 12+.

* The new :attr:`.ExclusionConstraint.opclasses` attribute allows setting
PostgreSQL operator classes.

* The new :attr:`.JSONBAgg.ordering` attribute determines the ordering of the
aggregated elements.

* The new :attr:`.JSONBAgg.distinct` attribute determines if aggregated values
will be distinct.

* The :class:`~django.contrib.postgres.operations.CreateExtension` operation
now checks that the extension already exists in the database and skips the
migration if so.

* The new :class:`~django.contrib.postgres.operations.CreateCollation` and
:class:`~django.contrib.postgres.operations.RemoveCollation` operations
allow creating and dropping collations on PostgreSQL. See
:ref:`manage-postgresql-collations` for more details.

* Lookups for :class:`~django.contrib.postgres.fields.ArrayField` now allow
(non-nested) arrays containing expressions as right-hand sides.

* The new :class:`OpClass() <django.contrib.postgres.indexes.OpClass>`
expression allows creating functional indexes on expressions with a custom
operator class. See :ref:`new_functional_indexes` for more details.

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

* The new :class:`~django.contrib.sitemaps.Sitemap` attributes
:attr:`~django.contrib.sitemaps.Sitemap.alternates`,
:attr:`~django.contrib.sitemaps.Sitemap.languages` and
:attr:`~django.contrib.sitemaps.Sitemap.x_default` allow
generating sitemap *alternates* to localized versions of your pages.

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

* The new ``item_comments`` hook allows specifying a comments URL per feed
item.

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

* Third-party database backends can now skip or mark as expected failures
tests in Django's test suite using the new
``DatabaseFeatures.django_test_skips`` and
``django_test_expected_failures`` attributes.

Decorators
~~~~~~~~~~

* The new :func:`~django.views.decorators.common.no_append_slash` decorator
allows individual views to be excluded from :setting:`APPEND_SLASH` URL
normalization.

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

* Custom :class:`~django.views.debug.ExceptionReporter` subclasses can now
define the :attr:`~django.views.debug.ExceptionReporter.html_template_path`
and :attr:`~django.views.debug.ExceptionReporter.text_template_path`
properties to override the templates used to render exception reports.

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

* The new :meth:`FileUploadHandler.upload_interrupted()
<django.core.files.uploadhandler.FileUploadHandler.upload_interrupted>`
callback allows handling interrupted uploads.

Forms
~~~~~

* The new ``absolute_max`` argument for :func:`.formset_factory`,
:func:`.inlineformset_factory`, and :func:`.modelformset_factory` allows
customizing the maximum number of forms that can be instantiated when
supplying ``POST`` data. See :ref:`formsets-absolute-max` for more details.

* The new ``can_delete_extra`` argument for :func:`.formset_factory`,
:func:`.inlineformset_factory`, and :func:`.modelformset_factory` allows
removal of the option to delete extra forms. See
:attr:`~.BaseFormSet.can_delete_extra` for more information.

* :class:`~django.forms.formsets.BaseFormSet` now reports a user facing error,
rather than raising an exception, when the management form is missing or has
been tampered with. To customize this error message, pass the
``error_messages`` argument with the key ``'missing_management_form'`` when
instantiating the formset.

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

* The ``week_format`` attributes of
:class:`~django.views.generic.dates.WeekMixin` and
:class:`~django.views.generic.dates.WeekArchiveView` now support the
``'%V'`` ISO 8601 week format.

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

* :djadmin:`loaddata` now supports fixtures stored in XZ archives (``.xz``)
and LZMA archives (``.lzma``).

* :djadmin:`dumpdata` now can compress data in the ``bz2``, ``gz``, ``lzma``,
or ``xz`` formats.

* :djadmin:`makemigrations` can now be called without an active database
connection. In that case, check for a consistent migration history is
skipped.

* :attr:`.BaseCommand.requires_system_checks` now supports specifying a list
of tags. System checks registered in the chosen tags will be checked for
errors prior to executing the command. In previous versions, either all or
none of the system checks were performed.

* Support for colored terminal output on Windows is updated. Various modern
terminal environments are automatically detected, and the options for
enabling support in other cases are improved. See :ref:`syntax-coloring` for
more details.

Migrations
~~~~~~~~~~

* The new ``Operation.migration_name_fragment`` property allows providing a
filename fragment that will be used to name a migration containing only that
operation.

* Migrations now support serialization of pure and concrete path objects from
:mod:`pathlib`, and :class:`os.PathLike` instances.

Models
~~~~~~

* The new ``no_key`` parameter for :meth:`.QuerySet.select_for_update()`,
supported on PostgreSQL, allows acquiring weaker locks that don't block the
creation of rows that reference locked rows through a foreign key.

* :class:`When() <django.db.models.expressions.When>` expression now allows
using the ``condition`` argument with ``lookups``.

* The new :attr:`.Index.include` and :attr:`.UniqueConstraint.include`
attributes allow creating covering indexes and covering unique constraints
on PostgreSQL 11+.

* The new :attr:`.UniqueConstraint.opclasses` attribute allows setting
PostgreSQL operator classes.

* The :meth:`.QuerySet.update` method now respects the ``order_by()`` clause
on MySQL and MariaDB.

* :class:`FilteredRelation() <django.db.models.FilteredRelation>` now supports
nested relations.

* The ``of`` argument of :meth:`.QuerySet.select_for_update()` is now allowed
on MySQL 8.0.1+.

* :class:`Value() <django.db.models.Value>` expression now
automatically resolves its ``output_field`` to the appropriate
:class:`Field <django.db.models.Field>` subclass based on the type of
its provided ``value`` for :py:class:`bool`, :py:class:`bytes`,
:py:class:`float`, :py:class:`int`, :py:class:`str`,
:py:class:`datetime.date`, :py:class:`datetime.datetime`,
:py:class:`datetime.time`, :py:class:`datetime.timedelta`,
:py:class:`decimal.Decimal`, and :py:class:`uuid.UUID` instances. As a
consequence, resolving an ``output_field`` for database functions and
combined expressions may now crash with mixed types when using ``Value()``.
You will need to explicitly set the ``output_field`` in such cases.

* The new :meth:`.QuerySet.alias` method allows creating reusable aliases for
expressions that don't need to be selected but are used for filtering,
ordering, or as a part of complex expressions.

* The new :class:`~django.db.models.functions.Collate` function allows
filtering and ordering by specified database collations.

* The ``field_name`` argument of :meth:`.QuerySet.in_bulk()` now accepts
distinct fields if there's only one field specified in
:meth:`.QuerySet.distinct`.

* The new ``tzinfo`` parameter of the
:class:`~django.db.models.functions.TruncDate` and
:class:`~django.db.models.functions.TruncTime` database functions allows
truncating datetimes in a specific timezone.

* The new ``db_collation`` argument for
:attr:`CharField <django.db.models.CharField.db_collation>` and
:attr:`TextField <django.db.models.TextField.db_collation>` allows setting a
database collation for the field.

* Added the :class:`~django.db.models.functions.Random` database function.

* :ref:`aggregation-functions`, :class:`F() <django.db.models.F>`,
:class:`OuterRef() <django.db.models.OuterRef>`, and other expressions now
allow using transforms. See :ref:`using-transforms-in-expressions` for
details.

* The new ``durable`` argument for :func:`~django.db.transaction.atomic`
guarantees that changes made in the atomic block will be committed if the
block exits without errors. A nested atomic block marked as durable will
raise a ``RuntimeError``.

* Added the :class:`~django.db.models.functions.JSONObject` database function.

Pagination
~~~~~~~~~~

* The new :meth:`django.core.paginator.Paginator.get_elided_page_range` method
allows generating a page range with some of the values elided. If there are
a large number of pages, this can be helpful for generating a reasonable
number of page links in a template.

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

* Response headers are now stored in :attr:`.HttpResponse.headers`. This can
be used instead of the original dict-like interface of ``HttpResponse``
objects. Both interfaces will continue to be supported. See
:ref:`setting-header-fields` for details.

* The new ``headers`` parameter of :class:`~django.http.HttpResponse`,
:class:`~django.template.response.SimpleTemplateResponse`, and
:class:`~django.template.response.TemplateResponse` allows setting response
:attr:`~django.http.HttpResponse.headers` on instantiation.

Security
~~~~~~~~

* The :setting:`SECRET_KEY` setting is now checked for a valid value upon
first access, rather than when settings are first loaded. This enables
running management commands that do not rely on the ``SECRET_KEY`` without
needing to provide a value. As a consequence of this, calling
:func:`~django.conf.settings.configure` without providing a valid
``SECRET_KEY``, and then going on to access ``settings.SECRET_KEY`` will now
raise an :exc:`~django.core.exceptions.ImproperlyConfigured` exception.

* The new ``Signer.sign_object()`` and ``Signer.unsign_object()`` methods
allow signing complex data structures. See :ref:`signing-complex-data` for
more details.

Also, :func:`signing.dumps() <django.core.signing.dumps>` and
:func:`~django.core.signing.loads` become shortcuts for
:meth:`.TimestampSigner.sign_object` and
:meth:`~.TimestampSigner.unsign_object`.

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

* The new :ref:`JSONL <serialization-formats-jsonl>` serializer allows using
the JSON Lines format with :djadmin:`dumpdata` and :djadmin:`loaddata`. This
can be useful for populating large databases because data is loaded line by
line into memory, rather than being loaded all at once.

Signals
~~~~~~~

* :meth:`Signal.send_robust() <django.dispatch.Signal.send_robust>` now logs
exceptions.

Templates
~~~~~~~~~

* :tfilter:`floatformat` template filter now allows using the ``g`` suffix to
force grouping by the :setting:`THOUSAND_SEPARATOR` for the active locale.

* Templates cached with :ref:`Cached template loaders<template-loaders>` are
now correctly reloaded in development.

Tests
~~~~~

* Objects assigned to class attributes in :meth:`.TestCase.setUpTestData` are
now isolated for each test method. Such objects are now required to support
creating deep copies with :py:func:`copy.deepcopy`. Assigning objects which
don't support ``deepcopy()`` is deprecated and will be removed in Django 4.1.

* :class:`~django.test.runner.DiscoverRunner` now enables
:py:mod:`faulthandler` by default. This can be disabled by using the
:option:`test --no-faulthandler` option.

* :class:`~django.test.runner.DiscoverRunner` and the
:djadmin:`test` management command can now track timings, including database
setup and total run time. This can be enabled by using the :option:`test
--timing` option.

* :class:`~django.test.Client` now preserves the request query string when
following 307 and 308 redirects.

* The new :meth:`.TestCase.captureOnCommitCallbacks` method captures callback
functions passed to :func:`transaction.on_commit()
<django.db.transaction.on_commit>` in a list. This allows you to test such
callbacks without using the slower :class:`.TransactionTestCase`.

* :meth:`.TransactionTestCase.assertQuerysetEqual` now supports direct
comparison against another queryset rather than being restricted to
comparison against a list of string representations of objects when using
the default value for the ``transform`` argument.

Utilities
~~~~~~~~~

* The new ``depth`` parameter of ``django.utils.timesince.timesince()`` and
``django.utils.timesince.timeuntil()`` functions allows specifying the
number of adjacent time units to return.

Validators
~~~~~~~~~~

* Built-in validators now include the provided value in the ``params``
argument of a raised :exc:`~django.core.exceptions.ValidationError`. This
allows custom error messages to use the ``%(value)s`` placeholder.

* The :class:`.ValidationError` equality operator now ignores ``messages`` and
``params`` ordering.

.. _backwards-incompatible-3.2:

Backwards incompatible changes in 3.2
=====================================

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

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

* The new ``DatabaseFeatures.introspected_field_types`` property replaces
these features:

* ``can_introspect_autofield``
* ``can_introspect_big_integer_field``
* ``can_introspect_binary_field``
* ``can_introspect_decimal_field``
* ``can_introspect_duration_field``
* ``can_introspect_ip_address_field``
* ``can_introspect_positive_integer_field``
* ``can_introspect_small_integer_field``
* ``can_introspect_time_field``
* ``introspected_big_auto_field_type``
* ``introspected_small_auto_field_type``
* ``introspected_boolean_field_type``

* To enable support for covering indexes (:attr:`.Index.include`) and covering
unique constraints (:attr:`.UniqueConstraint.include`), set
``DatabaseFeatures.supports_covering_indexes`` to ``True``.

* Third-party database backends must implement support for column database
collations on ``CharField``\s and ``TextField``\s or set
``DatabaseFeatures.supports_collation_on_charfield`` and
``DatabaseFeatures.supports_collation_on_textfield`` to ``False``. If
non-deterministic collations are not supported, set
``supports_non_deterministic_collations`` to ``False``.

* ``DatabaseOperations.random_function_sql()`` is removed in favor of the new
:class:`~django.db.models.functions.Random` database function.

* ``DatabaseOperations.date_trunc_sql()`` and
``DatabaseOperations.time_trunc_sql()`` now take the optional ``tzname``
argument in order to truncate in a specific timezone.

* ``DatabaseClient.runshell()`` now gets arguments and an optional dictionary
with environment variables to the underlying command-line client from
``DatabaseClient.settings_to_cmd_args_env()`` method. Third-party database
backends must implement ``DatabaseClient.settings_to_cmd_args_env()`` or
override ``DatabaseClient.runshell()``.

* Third-party database backends must implement support for functional indexes
(:attr:`.Index.expressions`) or set
``DatabaseFeatures.supports_expression_indexes`` to ``False``. If
``COLLATE`` is not a part of the ``CREATE INDEX`` statement, set
``DatabaseFeatures.collate_as_index_expression`` to ``True``.

:mod:`django.contrib.admin`
---------------------------

* Pagination links in the admin are now 1-indexed instead of 0-indexed, i.e.
the query string for the first page is ``?p=1`` instead of ``?p=0``.

* The new admin catch-all view will break URL patterns routed after the admin
URLs and matching the admin URL prefix. You can either adjust your URL
ordering or, if necessary, set :attr:`AdminSite.final_catch_all_view
<django.contrib.admin.AdminSite.final_catch_all_view>` to ``False``,
disabling the catch-all view. See :ref:`whats-new-3.2` for more details.

* Minified JavaScript files are no longer included with the admin. If you
require these files to be minified, consider using a third party app or
external build tool. The minified vendored JavaScript files packaged with
the admin (e.g. :ref:`jquery.min.js <contrib-admin-jquery>`) are still
included.

* :attr:`.ModelAdmin.prepopulated_fields` no longer strips English stop words,
such as ``'a'`` or ``'an'``.

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

* Support for PostGIS 2.2 is removed.

* The Oracle backend now clones polygons (and geometry collections containing
polygons) before reorienting them and saving them to the database. They are
no longer mutated in place. You might notice this if you use the polygons
after a model is saved.

Dropped support for PostgreSQL 9.5
----------------------------------

Upstream support for PostgreSQL 9.5 ends in February 2021. Django 3.2 supports
PostgreSQL 9.6 and higher.

Dropped support for MySQL 5.6
-----------------------------

The end of upstream support for MySQL 5.6 is April 2021. Django 3.2 supports
MySQL 5.7 and higher.

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

* Django now supports non-``pytz`` time zones, such as Python 3.9+'s
:mod:`zoneinfo` module and its backport.

* The undocumented ``SpatiaLiteOperations.proj4_version()`` method is renamed
to ``proj_version()``.

* :func:`~django.utils.text.slugify` now removes leading and trailing dashes
and underscores.

* The :tfilter:`intcomma` and :tfilter:`intword` template filters no longer
depend on the :setting:`USE_L10N` setting.

* Support for ``argon2-cffi`` < 19.1.0 is removed.

* The cache keys no longer includes the language when internationalization is
disabled (``USE_I18N = False``) and localization is enabled
(``USE_L10N = True``). After upgrading to Django 3.2 in such configurations,
the first request to any previously cached value will be a cache miss.

* ``ForeignKey.validate()`` now uses
:attr:`~django.db.models.Model._base_manager` rather than
:attr:`~django.db.models.Model._default_manager` to check that related
instances exist.

* When an application defines an :class:`~django.apps.AppConfig` subclass in
an ``apps.py`` submodule, Django now uses this configuration automatically,
even if it isn't enabled with ``default_app_config``. Set
``default = False`` in the :class:`~django.apps.AppConfig` subclass if you
need to prevent this behavior. See :ref:`whats-new-3.2` for more details.

* Instantiating an abstract model now raises ``TypeError``.

* Keyword arguments to :func:`~django.test.utils.setup_databases` are now
keyword-only.

* The undocumented ``django.utils.http.limited_parse_qsl()`` function is
removed. Please use :func:`urllib.parse.parse_qsl` instead.

* ``django.test.utils.TestContextDecorator`` now uses
:py:meth:`~unittest.TestCase.addCleanup` so that cleanups registered in the
:py:meth:`~unittest.TestCase.setUp` method are called before
``TestContextDecorator.disable()``.

* ``SessionMiddleware`` now raises a
:exc:`~django.contrib.sessions.exceptions.SessionInterrupted` exception
instead of :exc:`~django.core.exceptions.SuspiciousOperation` when a session
is destroyed in a concurrent request.

* The :class:`django.db.models.Field` equality operator now correctly
distinguishes inherited field instances across models. Additionally, the
ordering of such fields is now defined.

* The undocumented ``django.core.files.locks.lock()`` function now returns
``False`` if the file cannot be locked, instead of raising
:exc:`BlockingIOError`.

* The password reset mechanism now invalidates tokens when the user email is
changed.

* :djadmin:`makemessages` command no longer processes invalid locales
specified using :option:`makemessages --locale` option, when they contain
hyphens (``'-'``).

* The ``django.contrib.auth.forms.ReadOnlyPasswordHashField`` form field is
now :attr:`~django.forms.Field.disabled` by default. Therefore
``UserChangeForm.clean_password()`` is no longer required to return the
initial value.

* The ``cache.get_many()``, ``get_or_set()``, ``has_key()``, ``incr()``,
``decr()``, ``incr_version()``, and ``decr_version()`` cache operations now
correctly handle ``None`` stored in the cache, in the same way as any other
value, instead of behaving as though the key didn't exist.

Due to a ``python-memcached`` limitation, the previous behavior is kept for
the deprecated ``MemcachedCache`` backend.

* The minimum supported version of SQLite is increased from 3.8.3 to 3.9.0.

* :class:`~django.contrib.messages.storage.cookie.CookieStorage` now stores
messages in the :rfc:`6265` compliant format. Support for cookies that use
the old format remains until Django 4.1.

* The minimum supported version of ``asgiref`` is increased from 3.2.10 to
3.3.2.

.. _deprecated-features-3.2:

Features deprecated in 3.2
==========================

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

* Assigning objects which don't support creating deep copies with
:py:func:`copy.deepcopy` to class attributes in
:meth:`.TestCase.setUpTestData` is deprecated.

* Using a boolean value in :attr:`.BaseCommand.requires_system_checks` is
deprecated. Use ``'__all__'`` instead of ``True``, and ``[]`` (an empty
list) instead of ``False``.

* The ``whitelist`` argument and ``domain_whitelist`` attribute of
:class:`~django.core.validators.EmailValidator` are deprecated. Use
``allowlist`` instead of ``whitelist``, and ``domain_allowlist`` instead of
``domain_whitelist``. You may need to rename ``whitelist`` in existing
migrations.

* The ``default_app_config`` application configuration variable is deprecated,
due to the now automatic ``AppConfig`` discovery. See :ref:`whats-new-3.2`
for more details.

* Automatically calling ``repr()`` on a queryset in
``TransactionTestCase.assertQuerysetEqual()``, when compared to string
values, is deprecated. If you need the previous behavior, explicitly set
``transform`` to ``repr``.

* The ``django.core.cache.backends.memcached.MemcachedCache`` backend is
deprecated as ``python-memcached`` has some problems and seems to be
unmaintained. Use ``django.core.cache.backends.memcached.PyMemcacheCache``
or ``django.core.cache.backends.memcached.PyLibMCCache`` instead.

* The format of messages used by
``django.contrib.messages.storage.cookie.CookieStorage`` is different from
the format generated by older versions of Django. Support for the old format
remains until Django 4.1.


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

3.1.8

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

*April 6, 2021*

Django 3.1.8 fixes a security issue with severity "low" and a bug in 3.1.7.

CVE-2021-28658: Potential directory-traversal via uploaded files
================================================================

``MultiPartParser`` allowed directory-traversal via uploaded files with
suitably crafted file names.

Built-in upload handlers were not affected by this vulnerability.

Bugfixes
========

* Fixed a bug in Django 3.1 where the output was hidden on a test error or
failure when using :option:`test --pdb` with the
:option:`--buffer <test --buffer>` option (:ticket:`32560`).


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

3.1.7

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

*February 19, 2021*

Django 3.1.7 fixes a security issue and a bug in 3.1.6.

CVE-2021-23336: Web cache poisoning via ``django.utils.http.limited_parse_qsl()``
=================================================================================

Django contains a copy of :func:`urllib.parse.parse_qsl` which was added to
backport some security fixes. A further security fix has been issued recently
such that ``parse_qsl()`` no longer allows using ``;`` as a query parameter
separator by default. Django now includes this fix. See :bpo:`42967` for
further details.

Bugfixes
========

* Fixed a regression in Django 3.1 that caused ``RuntimeError`` instead of
connection errors when using only the ``'postgres'`` database
(:ticket:`32403`).


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

3.1.6

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

*February 1, 2021*

Django 3.1.6 fixes a security issue with severity "low" and a bug in 3.1.5.

CVE-2021-3281: Potential directory-traversal via ``archive.extract()``
======================================================================

The ``django.utils.archive.extract()`` function, used by
:option:`startapp --template` and :option:`startproject --template`, allowed
directory-traversal via an archive with absolute paths or relative paths with
dot segments.

Bugfixes
========

* Fixed an admin layout issue in Django 3.1 where changelist filter controls 
would become squashed (:ticket:`32391`).


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

3.1.5

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

*January 4, 2021*

Django 3.1.5 fixes several bugs in 3.1.4.

Bugfixes
========

* Fixed ``__isnull=True`` lookup on key transforms for
:class:`~django.db.models.JSONField` with Oracle and SQLite
(:ticket:`32252`).

* Fixed a bug in Django 3.1 that caused a crash when processing middlewares in
an async context with a middleware that raises a ``MiddlewareNotUsed``
exception (:ticket:`32299`).

* Fixed a regression in Django 3.1 that caused the incorrect prefixing of
``STATIC_URL`` and ``MEDIA_URL`` settings, by the server-provided value of
``SCRIPT_NAME`` (or ``/`` if not set), when set to a URL specifying the
protocol but without a top-level domain, e.g. ``http://myhost/``
(:ticket:`32304`).


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

3.1.4

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

*December 1, 2020*

Django 3.1.4 fixes several bugs in 3.1.3.

Bugfixes
========

* Fixed setting the ``Content-Length`` HTTP header in ``AsyncRequestFactory``
(:ticket:`32162`).

* Fixed passing extra HTTP headers to ``AsyncRequestFactory`` request methods
(:ticket:`32159`).

* Fixed crash of key transforms for :class:`~django.db.models.JSONField` on
PostgreSQL when using on a ``Subquery()`` annotation (:ticket:`32182`).

* Fixed a regression in Django 3.1 that caused a crash of auto-reloader for
certain invocations of ``runserver`` on Windows with Python 3.7 and below
(:ticket:`32202`).

* Fixed a regression in Django 3.1 that caused the incorrect grouping by a
``Q`` object annotation (:ticket:`32200`).

* Fixed a regression in Django 3.1 that caused suppressing connection errors
when :class:`~django.db.models.JSONField` is used on SQLite
(:ticket:`32224`).

* Fixed a crash on SQLite, when ``QuerySet.values()/values_list()`` contained
key transforms for :class:`~django.db.models.JSONField` returning non-string
primitive values (:ticket:`32203`).


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

3.1.3

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

*November 2, 2020*

Django 3.1.3 fixes several bugs in 3.1.2 and adds compatibility with Python
3.9.

Bugfixes
========

* Fixed a regression in Django 3.1.2 that caused the incorrect height of the
admin changelist search bar (:ticket:`32072`).

* Fixed a regression in Django 3.1.2 that caused the incorrect width of the
admin changelist search bar on a filtered page (:ticket:`32091`).

* Fixed displaying Unicode characters in
:class:`forms.JSONField <django.forms.JSONField>` and read-only
:class:`models.JSONField <django.db.models.JSONField>` values in the admin
(:ticket:`32080`).

* Fixed a regression in Django 3.1 that caused a crash of
:class:`~django.contrib.postgres.aggregates.ArrayAgg` and
:class:`~django.contrib.postgres.aggregates.StringAgg` with ``ordering``
on key transforms for :class:`~django.db.models.JSONField` (:ticket:`32096`).

* Fixed a regression in Django 3.1 that caused a crash of ``__in`` lookup when
using key transforms for :class:`~django.db.models.JSONField` in the lookup
value (:ticket:`32096`).

* Fixed a regression in Django 3.1 that caused a crash of
:class:`~django.db.models.ExpressionWrapper` with key transforms for
:class:`~django.db.models.JSONField` (:ticket:`32096`).

* Fixed a regression in Django 3.1 that caused a migrations crash on PostgreSQL
when adding an
:class:`~django.contrib.postgres.constraints.ExclusionConstraint` with key
transforms for :class:`~django.db.models.JSONField` in ``expressions``
(:ticket:`32096`).

* Fixed a regression in Django 3.1 where
:exc:`ProtectedError.protected_objects <django.db.models.ProtectedError>` and
:exc:`RestrictedError.restricted_objects <django.db.models.RestrictedError>`
attributes returned iterators instead of :py:class:`set` of objects
(:ticket:`32107`).

* Fixed a regression in Django 3.1.2 that caused incorrect form input layout on
small screens in the admin change form view (:ticket:`32069`).

* Fixed a regression in Django 3.1 that invalidated pre-Django 3.1 password
reset tokens (:ticket:`32130`).

* Added support for ``asgiref`` 3.3 (:ticket:`32128`).

* Fixed a regression in Django 3.1 that caused incorrect textarea layout on
medium-sized screens in the admin change form view with the sidebar open
(:ticket:`32127`).

* Fixed a regression in Django 3.0.7 that didn't use ``Subquery()`` aliases in
the ``GROUP BY`` clause (:ticket:`32152`).


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

3.1.2

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

*October 1, 2020*

Django 3.1.2 fixes several bugs in 3.1.1.

Bugfixes
========

* Fixed a bug in Django 3.1 where ``FileField`` instances with a callable
storage were not correctly deconstructed (:ticket:`31941`).

* Fixed a regression in Django 3.1 where the :attr:`.QuerySet.ordered`
attribute returned incorrectly ``True`` for ``GROUP BY`` queries (e.g.
``.annotate().values()``) on models with ``Meta.ordering``. A model's
``Meta.ordering`` doesn't affect such queries (:ticket:`31990`).

* Fixed a regression in Django 3.1 where a queryset would crash if it contained
an aggregation and a ``Q`` object annotation (:ticket:`32007`).

* Fixed a bug in Django 3.1 where a test database was not synced during
creation when using the :setting:`MIGRATE <TEST_MIGRATE>` test database
setting (:ticket:`32012`).

* Fixed a ``django.contrib.admin.EmptyFieldListFilter`` crash when using on a
``GenericRelation`` (:ticket:`32038`).

* Fixed a regression in Django 3.1.1 where the admin changelist filter sidebar
would not scroll for a long list of available filters (:ticket:`31986`).


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

3.1.1

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

*September 1, 2020*

Django 3.1.1 fixes two security issues and several bugs in 3.1.

CVE-2020-24583: Incorrect permissions on intermediate-level directories on Python 3.7+
======================================================================================

On Python 3.7+, :setting:`FILE_UPLOAD_DIRECTORY_PERMISSIONS` mode was not
applied to intermediate-level directories created in the process of uploading
files and to intermediate-level collected static directories when using the
:djadmin:`collectstatic` management command.

You should review and manually fix permissions on existing intermediate-level
directories.

CVE-2020-24584: Permission escalation in intermediate-level directories of the file system cache on Python 3.7+
===============================================================================================================

On Python 3.7+, the intermediate-level directories of the file system cache had
the system's standard umask rather than ``0o077`` (no group or others
permissions).

Bugfixes
========

* Fixed wrapping of translated action labels in the admin's navigation sidebar
for East Asian languages (:ticket:`31853`).

* Fixed wrapping of long model names in the admin's navigation sidebar
(:ticket:`31854`).

* Fixed encoding session data while upgrading multiple instances of the same
project to Django 3.1 (:ticket:`31864`).

* Adjusted admin's navigation sidebar template to reduce debug logging when
rendering (:ticket:`31865`).

* Fixed a data loss possibility in the
:meth:`~django.db.models.query.QuerySet.select_for_update()`. When using
related fields pointing to a proxy model in the ``of`` argument, the
corresponding model was not locked (:ticket:`31866`).

* Fixed a data loss possibility, following a regression in Django 2.0, when
copying model instances with a cached fields value (:ticket:`31863`).

* Fixed a regression in Django 3.1 that caused a crash when decoding an invalid
session data (:ticket:`31895`).

* Reverted a deprecation in Django 3.1 that caused a crash when passing
deprecated keyword arguments to a queryset in
``TemplateView.get_context_data()`` (:ticket:`31877`).

* Enforced thread sensitivity of the :class:`MiddlewareMixin.process_request()
<django.utils.deprecation.MiddlewareMixin>` and ``process_response()`` hooks
when in an async context (:ticket:`31905`).

* Fixed ``__in`` lookup on key transforms for
:class:`~django.db.models.JSONField` with MariaDB, MySQL, Oracle, and SQLite
(:ticket:`31936`).

* Fixed a regression in Django 3.1 that caused permission errors in
``CommonPasswordValidator`` and ``settings.py`` generated by the
:djadmin:`startproject` command, when user didn't have permissions to all
intermediate directories in a Django installation path (:ticket:`31912`).

* Fixed detecting an async ``get_response`` callable in various builtin
middlewares (:ticket:`31928`).

* Fixed a ``QuerySet.order_by()`` crash on PostgreSQL when ordering and
grouping by :class:`~django.db.models.JSONField` with a custom
:attr:`~django.db.models.JSONField.decoder` (:ticket:`31956`). As a
consequence, fetching a ``JSONField`` with raw SQL now returns a string
instead of pre-loaded data. You will need to explicitly call ``json.loads()``
in such cases.

* Fixed a ``QuerySet.delete()`` crash on MySQL, following a performance
regression in Django 3.1 on MariaDB 10.3.2+, when filtering against an
aggregate function (:ticket:`31965`).

* Fixed a ``django.contrib.admin.EmptyFieldListFilter`` crash when using on
reverse relations (:ticket:`31952`).

* Prevented content overflowing in the admin changelist view when the
navigation sidebar is enabled (:ticket:`31901`).


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

3.1

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

*August 4, 2020*

Welcome to Django 3.1!

These release notes cover the :ref:`new features <whats-new-3.1>`, as well as
some :ref:`backwards incompatible changes <backwards-incompatible-3.1>` you'll
want to be aware of when upgrading from Django 3.0 or earlier. We've
:ref:`dropped some features<removed-features-3.1>` that have reached the end of
their deprecation cycle, and we've :ref:`begun the deprecation process for
some features <deprecated-features-3.1>`.

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

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

Django 3.1 supports Python 3.6, 3.7, 3.8, and 3.9 (as of 3.1.3). We **highly
recommend** and only officially support the latest release of each series.

.. _whats-new-3.1:

What's new in Django 3.1
========================

Asynchronous views and middleware support
-----------------------------------------

Django now supports a fully asynchronous request path, including:

* :ref:`Asynchronous views <async-views>`
* :ref:`Asynchronous middleware <async-middleware>`
* :ref:`Asynchronous tests and test client <async-tests>`

To get started with async views, you need to declare a view using
``async def``::

 async def my_view(request):
     await asyncio.sleep(0.5)
     return HttpResponse('Hello, async world!')

All asynchronous features are supported whether you are running under WSGI or
ASGI mode. However, there will be performance penalties using async code in
WSGI mode. You can read more about the specifics in :doc:`/topics/async`
documentation.

You are free to mix async and sync views, middleware, and tests as much as you
want. Django will ensure that you always end up with the right execution
context. We expect most projects will keep the majority of their views
synchronous, and only have a select few running in async mode - but it is
entirely your choice.

Django's ORM, cache layer, and other pieces of code that do long-running
network calls do not yet support async access. We expect to add support for
them in upcoming releases. Async views are ideal, however, if you are doing a
lot of API or HTTP calls inside your view, you can now natively do all those
HTTP calls in parallel to considerably speed up your view's execution.

Asynchronous support should be entirely backwards-compatible and we have tried
to ensure that it has no speed regressions for your existing, synchronous code.
It should have no noticeable effect on any existing Django projects.

JSONField for all supported database backends
---------------------------------------------

Django now includes :class:`.models.JSONField` and
:class:`forms.JSONField <django.forms.JSONField>` that can be used on all
supported database backends. Both fields support the use of custom JSON
encoders and decoders. The model field supports the introspection,
:ref:`lookups, and transforms <querying-jsonfield>` that were previously
PostgreSQL-only::

 from django.db import models

 class ContactInfo(models.Model):
     data = models.JSONField()

 ContactInfo.objects.create(data={
     'name': 'John',
     'cities': ['London', 'Cambridge'],
     'pets': {'dogs': ['Rufus', 'Meg']},
 })
 ContactInfo.objects.filter(
     data__name='John',
     data__pets__has_key='dogs',
     data__cities__contains='London',
 ).delete()

If your project uses ``django.contrib.postgres.fields.JSONField``, plus the
related form field and transforms, you should adjust to use the new fields,
and generate and apply a database migration. For now, the old fields and
transforms are left as a reference to the new ones and are :ref:`deprecated as
of this release <deprecated-jsonfield>`.

.. _default-hashing-algorithm-usage:

``DEFAULT_HASHING_ALGORITHM`` settings
--------------------------------------

The new ``DEFAULT_HASHING_ALGORITHM`` transitional setting allows specifying
the default hashing algorithm to use for encoding cookies, password reset
tokens in the admin site, user sessions, and signatures created by
:class:`django.core.signing.Signer` and :meth:`django.core.signing.dumps`.

Support for SHA-256 was added in Django 3.1. If you are upgrading multiple
instances of the same project to Django 3.1, you should set
``DEFAULT_HASHING_ALGORITHM`` to ``'sha1'`` during the transition, in order to
allow compatibility with the older versions of Django. Note that this requires
Django 3.1.1+. Once the transition to 3.1 is complete you can stop overriding
``DEFAULT_HASHING_ALGORITHM``.

This setting is deprecated as of this release, because support for tokens,
cookies, sessions, and signatures that use SHA-1 algorithm will be removed in
Django 4.0.

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

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

* The new ``django.contrib.admin.EmptyFieldListFilter`` for
:attr:`.ModelAdmin.list_filter` allows filtering on empty values (empty
strings and nulls) in the admin changelist view.

* Filters in the right sidebar of the admin changelist view now contain a link
to clear all filters.

* The admin now has a sidebar on larger screens for easier navigation. It is
enabled by default but can be disabled by using a custom ``AdminSite`` and
setting :attr:`.AdminSite.enable_nav_sidebar` to ``False``.

Rendering the sidebar requires access to the current request in order to set
CSS and ARIA role affordances. This requires using
``'django.template.context_processors.request'`` in the
``'context_processors'`` option of :setting:`OPTIONS <TEMPLATES-OPTIONS>`.

* Initially empty ``extra`` inlines can now be removed, in the same way as
dynamically created ones.

* ``XRegExp`` is upgraded from version 2.0.0 to 3.2.0.

* jQuery is upgraded from version 3.4.1 to 3.5.1.

* Select2 library is upgraded from version 4.0.7 to 4.0.13.

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

* The default iteration count for the PBKDF2 password hasher is increased from
180,000 to 216,000.

* The new :setting:`PASSWORD_RESET_TIMEOUT` setting allows defining the number
of seconds a password reset link is valid for. This is encouraged instead of
the deprecated ``PASSWORD_RESET_TIMEOUT_DAYS`` setting, which will be removed
in Django 4.0.

* The password reset mechanism now uses the SHA-256 hashing algorithm. Support
for tokens that use the old hashing algorithm remains until Django 4.0.

* :meth:`.AbstractBaseUser.get_session_auth_hash` now uses the SHA-256 hashing
algorithm. Support for user sessions that use the old hashing algorithm
remains until Django 4.0.

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

* The new :option:`remove_stale_contenttypes --include-stale-apps` option
allows removing stale content types from previously installed apps that have
been removed from :setting:`INSTALLED_APPS`.

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

* :lookup:`relate` lookup is now supported on MariaDB.

* Added the :attr:`.LinearRing.is_counterclockwise` property.

* :class:`~django.contrib.gis.db.models.functions.AsGeoJSON` is now supported
on Oracle.

* Added the :class:`~django.contrib.gis.db.models.functions.AsWKB` and
:class:`~django.contrib.gis.db.models.functions.AsWKT` functions.

* Added support for PostGIS 3 and GDAL 3.

:mod:`django.contrib.humanize`
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

* :tfilter:`intword` template filter now supports negative integers.

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

* The new :class:`~django.contrib.postgres.indexes.BloomIndex` class allows
creating ``bloom`` indexes in the database. The new
:class:`~django.contrib.postgres.operations.BloomExtension` migration
operation installs the ``bloom`` extension to add support for this index.

* :meth:`~django.db.models.Model.get_FOO_display` now supports
:class:`~django.contrib.postgres.fields.ArrayField` and
:class:`~django.contrib.postgres.fields.RangeField`.

* The new :lookup:`rangefield.lower_inc`, :lookup:`rangefield.lower_inf`,
:lookup:`rangefield.upper_inc`, and :lookup:`rangefield.upper_inf` lookups
allow querying :class:`~django.contrib.postgres.fields.RangeField` by a bound
type.

* :lookup:`rangefield.contained_by` now supports
:class:`~django.db.models.SmallAutoField`,
:class:`~django.db.models.AutoField`,
:class:`~django.db.models.BigAutoField`,
:class:`~django.db.models.SmallIntegerField`, and
:class:`~django.db.models.DecimalField`.

* :class:`~django.contrib.postgres.search.SearchQuery` now supports
``'websearch'`` search type on PostgreSQL 11+.

* :class:`SearchQuery.value <django.contrib.postgres.search.SearchQuery>` now
supports query expressions.

* The new :class:`~django.contrib.postgres.search.SearchHeadline` class allows
highlighting search results.

* :lookup:`search` lookup now supports query expressions.

* The new ``cover_density`` parameter of
:class:`~django.contrib.postgres.search.SearchRank` allows ranking by cover
density.

* The new ``normalization`` parameter of
:class:`~django.contrib.postgres.search.SearchRank` allows rank
normalization.

* The new :attr:`.ExclusionConstraint.deferrable` attribute allows creating
deferrable exclusion constraints.

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

* The :setting:`SESSION_COOKIE_SAMESITE` setting now allows ``'None'`` (string)
value to explicitly state that the cookie is sent with all same-site and
cross-site requests.

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

* The :setting:`STATICFILES_DIRS` setting now supports :class:`pathlib.Path`.

Cache
~~~~~

* The :func:`~django.views.decorators.cache.cache_control` decorator and
:func:`~django.utils.cache.patch_cache_control` method now support multiple
field names in the ``no-cache`` directive for the ``Cache-Control`` header,
according to :rfc:`7234section-5.2.2.2`.

* :meth:`~django.core.caches.cache.delete` now returns ``True`` if the key was
successfully deleted, ``False`` otherwise.

CSRF
~~~~

* The :setting:`CSRF_COOKIE_SAMESITE` setting now allows ``'None'`` (string)
value to explicitly state that the cookie is sent with all same-site and
cross-site requests.

Email
~~~~~

* The :setting:`EMAIL_FILE_PATH` setting, used by the :ref:`file email backend
<topic-email-file-backend>`, now supports :class:`pathlib.Path`.

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

* :class:`django.views.debug.SafeExceptionReporterFilter` now filters sensitive
values from ``request.META`` in exception reports.

* The new :attr:`.SafeExceptionReporterFilter.cleansed_substitute` and
:attr:`.SafeExceptionReporterFilter.hidden_settings` attributes allow
customization of sensitive settings and ``request.META`` filtering in
exception reports.

* The technical 404 debug view now respects
:setting:`DEFAULT_EXCEPTION_REPORTER_FILTER` when applying settings
filtering.

* The new :setting:`DEFAULT_EXCEPTION_REPORTER` allows providing a
:class:`django.views.debug.ExceptionReporter` subclass to customize exception
report generation. See :ref:`custom-error-reports` for details.

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

* ``FileSystemStorage.save()`` method now supports :class:`pathlib.Path`.

* :class:`~django.db.models.FileField` and
:class:`~django.db.models.ImageField` now accept a callable for ``storage``.
This allows you to modify the used storage at runtime, selecting different
storages for different environments, for example.

Forms
~~~~~

* :class:`~django.forms.ModelChoiceIterator`, used by
:class:`~django.forms.ModelChoiceField` and
:class:`~django.forms.ModelMultipleChoiceField`, now uses
:class:`~django.forms.ModelChoiceIteratorValue` that can be used by widgets
to access model instances. See :ref:`iterating-relationship-choices` for
details.

* :class:`django.forms.DateTimeField` now accepts dates in a subset of ISO 8601
datetime formats, including optional timezone, e.g. ``2019-10-10T06:47``,
``2019-10-10T06:47:23+04:00``, or ``2019-10-10T06:47:23Z``. The timezone will
always be retained if provided, with timezone-aware datetimes being returned
even when :setting:`USE_TZ` is ``False``.

Additionally, ``DateTimeField`` now uses ``DATE_INPUT_FORMATS`` in addition
to ``DATETIME_INPUT_FORMATS`` when converting a field input to a ``datetime``
value.

* :attr:`.MultiWidget.widgets` now accepts a dictionary which allows
customizing subwidget ``name`` attributes.

* The new :attr:`.BoundField.widget_type` property can be used to dynamically
adjust form rendering based upon the widget type.

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

* The :setting:`LANGUAGE_COOKIE_SAMESITE` setting now allows ``'None'``
(string) value to explicitly state that the cookie is sent with all same-site
and cross-site requests.

* Added support and translations for the Algerian Arabic, Igbo, Kyrgyz, Tajik,
and Turkmen languages.

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

* The new :option:`check --database` option allows specifying database aliases
for running the ``database`` system checks. Previously these checks were
enabled for all configured :setting:`DATABASES` by passing the ``database``
tag to the command.

* The new :option:`migrate --check` option makes the command exit with a
non-zero status when unapplied migrations are detected.

* The new ``returncode`` argument for
:attr:`~django.core.management.CommandError` allows customizing the exit
status for management commands.

* The new :option:`dbshell -- ARGUMENTS <dbshell -->` option allows passing
extra arguments to the command-line client for the database.

* The :djadmin:`flush` and :djadmin:`sqlflush` commands now include SQL to
reset sequences on SQLite.

Models
~~~~~~

* The new :class:`~django.db.models.functions.ExtractIsoWeekDay` function
extracts ISO-8601 week days from :class:`~django.db.models.DateField` and
:class:`~django.db.models.DateTimeField`, and the new :lookup:`iso_week_day`
lookup allows querying by an ISO-8601 day of week.

* :meth:`.QuerySet.explain` now supports:

* ``TREE`` format on MySQL 8.0.16+,
* ``analyze`` option on MySQL 8.0.18+ and MariaDB.

* Added :class:`~django.db.models.PositiveBigIntegerField` which acts much like
a :class:`~django.db.models.PositiveIntegerField` except that it only allows
values under a certain (database-dependent) limit. Values from ``0`` to
``9223372036854775807`` are safe in all databases supported by Django.

* The new :class:`~django.db.models.RESTRICT` option for
:attr:`~django.db.models.ForeignKey.on_delete` argument of ``ForeignKey`` and
``OneToOneField`` emulates the behavior of the SQL constraint ``ON DELETE
RESTRICT``.

* :attr:`.CheckConstraint.check` now supports boolean expressions.

* The :meth:`.RelatedManager.add`, :meth:`~.RelatedManager.create`, and
:meth:`~.RelatedManager.set` methods now accept callables as values in the
``through_defaults`` argument.

* The new ``is_dst``  parameter of the :meth:`.QuerySet.datetimes` determines
the treatment of nonexistent and ambiguous datetimes.

* The new :class:`~django.db.models.F` expression ``bitxor()`` method allows
:ref:`bitwise XOR operation <using-f-expressions-in-filters>`.

* :meth:`.QuerySet.bulk_create` now sets the primary key on objects when using
MariaDB 10.5+.

* The ``DatabaseOperations.sql_flush()`` method now generates more efficient
SQL on MySQL by using ``DELETE`` instead of ``TRUNCATE`` statements for
tables which don't require resetting sequences.

* SQLite functions are now marked as :py:meth:`deterministic
<sqlite3.Connection.create_function>` on Python 3.8+. This allows using them
in check constraints and partial indexes.

* The new :attr:`.UniqueConstraint.deferrable` attribute allows creating
deferrable unique constraints.

Pagination
~~~~~~~~~~

* :class:`~django.core.paginator.Paginator` can now be iterated over to yield
its pages.

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

* If :setting:`ALLOWED_HOSTS` is empty and ``DEBUG=True``, subdomains of
localhost are now allowed in the ``Host`` header, e.g. ``static.localhost``.

* :meth:`.HttpResponse.set_cookie` and :meth:`.HttpResponse.set_signed_cookie`
now allow using ``samesite='None'`` (string) to explicitly state that the
cookie is sent with all same-site and cross-site requests.

* The new :meth:`.HttpRequest.accepts` method returns whether the request
accepts the given MIME type according to the ``Accept`` HTTP header.

.. _whats-new-security-3.1:

Security
~~~~~~~~

* The :setting:`SECURE_REFERRER_POLICY` setting now defaults to
``'same-origin'``. With this configured,
:class:`~django.middleware.security.SecurityMiddleware` sets the
:ref:`referrer-policy` header to ``same-origin`` on all responses that do not
already have it. This prevents the ``Referer`` header being sent to other
origins. If you need the previous behavior, explicitly set
:setting:`SECURE_REFERRER_POLICY` to ``None``.

* The default algorithm of :class:`django.core.signing.Signer`,
:meth:`django.core.signing.loads`, and :meth:`django.core.signing.dumps` is
changed to the SHA-256. Support for signatures made with the old SHA-1
algorithm remains until Django 4.0.

Also, the new ``algorithm`` parameter of the
:class:`~django.core.signing.Signer` allows customizing the hashing
algorithm.

Templates
~~~~~~~~~

* The renamed :ttag:`translate` and :ttag:`blocktranslate` template tags are
introduced for internationalization in template code. The older :ttag:`trans`
and :ttag:`blocktrans` template tags aliases continue to work, and will be
retained for the foreseeable future.

* The :ttag:`include` template tag now accepts iterables of template names.

Tests
~~~~~

* :class:`~django.test.SimpleTestCase` now implements the ``debug()`` method to
allow running a test without collecting the result and catching exceptions.
This can be used to support running tests under a debugger.

* The new :setting:`MIGRATE <TEST_MIGRATE>` test database setting allows
disabling of migrations during a test database creation.

* Django test runner now supports a :option:`test --buffer` option to discard
output for passing tests.

* :class:`~django.test.runner.DiscoverRunner` now skips running the system
checks on databases not :ref:`referenced by tests<testing-multi-db>`.

* :class:`~django.test.TransactionTestCase` teardown is now faster on MySQL
due to :djadmin:`flush` command improvements. As a side effect the latter
doesn't automatically reset sequences on teardown anymore. Enable
:attr:`.TransactionTestCase.reset_sequences` if your tests require this
feature.

URLs
~~~~

* :ref:`Path converters <registering-custom-path-converters>` can now raise
``ValueError`` in ``to_url()`` to indicate no match when reversing URLs.

Utilities
~~~~~~~~~

* :func:`~django.utils.encoding.filepath_to_uri` now supports
:class:`pathlib.Path`.

* :func:`~django.utils.dateparse.parse_duration` now supports comma separators
for decimal fractions in the ISO 8601 format.

* :func:`~django.utils.dateparse.parse_datetime`,
:func:`~django.utils.dateparse.parse_duration`, and
:func:`~django.utils.dateparse.parse_time` now support comma separators for
milliseconds.

Miscellaneous
~~~~~~~~~~~~~

* The SQLite backend now supports :class:`pathlib.Path` for the ``NAME``
setting.

* The ``settings.py`` generated by the :djadmin:`startproject` command now uses
:class:`pathlib.Path` instead of :mod:`os.path` for building filesystem
paths.

* The :setting:`TIME_ZONE <DATABASE-TIME_ZONE>` setting is now allowed on
databases that support time zones.

.. _backwards-incompatible-3.1:

Backwards incompatible changes in 3.1
=====================================

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

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

* ``DatabaseOperations.fetch_returned_insert_columns()`` now requires an
additional ``returning_params`` argument.

* ``connection.timezone`` property is now ``'UTC'`` by default, or the
:setting:`TIME_ZONE <DATABASE-TIME_ZONE>` when :setting:`USE_TZ` is ``True``
on databases that support time zones. Previously, it was ``None`` on
databases that support time zones.

* ``connection._nodb_connection`` property is changed to the
``connection._nodb_cursor()`` method and now returns a context manager that
yields a cursor and automatically closes the cursor and connection upon
exiting the ``with`` statement.

* ``DatabaseClient.runshell()`` now requires an additional ``parameters``
argument as a list of extra arguments to pass on to the command-line client.

* The ``sequences`` positional argument of ``DatabaseOperations.sql_flush()``
is replaced by the boolean keyword-only argument ``reset_sequences``. If
``True``, the sequences of the truncated tables will be reset.

* The ``allow_cascade`` argument of ``DatabaseOperations.sql_flush()`` is now a
keyword-only argument.

* The ``using`` positional argument of
``DatabaseOperations.execute_sql_flush()`` is removed. The method now uses
the database of the called instance.

* Third-party database backends must implement support for ``JSONField`` or set
``DatabaseFeatures.supports_json_field`` to ``False``. If sto