# Django 5.2.16 documentation

# Django 4.0 release notes

December 7, 2021

Welcome to Django 4.0!

These release notes cover the new features, as well as some backwards incompatible changes you’ll want to be aware of when upgrading from Django 3.2 or earlier. We’ve begun the deprecation process for some features.

See the How to upgrade Django to a newer version guide if you’re updating an existing project.

## Python compatibility

Django 4.0 supports Python 3.8, 3.9, and 3.10. We highly recommend and only officially support the latest release of each series.

The Django 3.2.x series is the last to support Python 3.6 and 3.7.

## What’s new in Django 4.0

### `zoneinfo` default timezone implementation

The Python standard library’s `zoneinfo` is now the default timezone implementation in Django.

This is the next step in the migration from using `pytz` to using `zoneinfo`. Django 3.2 allowed the use of non-`pytz` time zones. Django 4.0 makes `zoneinfo` the default implementation. Support for `pytz` is now deprecated and will be removed in Django 5.0.

`zoneinfo` is part of the Python standard library from Python 3.9. The `backports.zoneinfo` package is automatically installed alongside Django if you are using Python 3.8.

The move to `zoneinfo` should be largely transparent. Selection of the current timezone, conversion of datetime instances to the current timezone in forms and templates, as well as operations on aware datetimes in UTC are unaffected.

However, if you are working with non-UTC time zones, and using the `pytz` `normalize()` and `localize()` APIs, possibly with the `TIME_ZONE` setting, you will need to audit your code, since `pytz` and `zoneinfo` are not entirely equivalent.

To give time for such an audit, the transitional `USE_DEPRECATED_PYTZ` setting allows continued use of `pytz` during the 4.x release cycle. This setting will be removed in Django 5.0.

In addition, a pytz_deprecation_shim package, created by the `zoneinfo` author, can be used to assist with the migration from `pytz`. This package provides shims to help you safely remove `pytz`, and has a detailed migration guide showing how to move to the new `zoneinfo` APIs.

Using pytz_deprecation_shim and the `USE_DEPRECATED_PYTZ` transitional setting is recommended if you need a gradual update path.

### Functional unique constraints

The new `*expressions` positional argument of `UniqueConstraint()` enables creating functional unique constraints on expressions and database functions. For example:

    from django.db import models
    from django.db.models import UniqueConstraint
    from django.db.models.functions import Lower

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

        class Meta:
            constraints = [
                UniqueConstraint(
                    Lower("first_name"),
                    Lower("last_name").desc(),
                    name="first_last_name_unique",
                ),
            ]

Functional unique constraints are added to models using the `Meta.constraints` option.

### `scrypt` password hasher

The new scrypt password hasher is more secure and recommended over PBKDF2. However, it’s not the default as it requires OpenSSL 1.1+ and more memory.

### Redis cache backend

The new `django.core.cache.backends.redis.RedisCache` cache backend provides built-in support for caching with Redis. redis-py 3.0.0 or higher is required. For more details, see the documentation on caching with Redis in Django.

### Template based form rendering

`Forms`, Formsets, and `ErrorList` are now rendered using the template engine to enhance customization. See the new `render()`, `get_context()`, and `template_name` for `Form` and formset rendering for `Formset`.

### Minor features

#### `django.contrib.admin`

- The `admin/base.html` template now has a new block `header` which contains the admin site header.

- The new `ModelAdmin.get_formset_kwargs()` method allows customizing the keyword arguments passed to the constructor of a formset.

- The navigation sidebar now has a quick filter toolbar.

- The new context variable `model` which contains the model class for each model is added to the `AdminSite.each_context()` method.

- The new `ModelAdmin.search_help_text` attribute allows specifying a descriptive text for the search box.

- The `InlineModelAdmin.verbose_name_plural` attribute now fallbacks to the `InlineModelAdmin.verbose_name` + `'s'`.

- jQuery is upgraded from version 3.5.1 to 3.6.0.

#### `django.contrib.admindocs`

- The admindocs now allows esoteric setups where `ROOT_URLCONF` is not a string.

- The model section of the `admindocs` now shows cached properties.

#### `django.contrib.auth`

- The default iteration count for the PBKDF2 password hasher is increased from 260,000 to 320,000.

- The new `LoginView.next_page` attribute and `get_default_redirect_url()` method allow customizing the redirect after login.

#### `django.contrib.gis`

- Added support for SpatiaLite 5.

- `GDALRaster` now allows creating rasters in any GDAL virtual filesystem.

- The new `GISModelAdmin` class allows customizing the widget used for `GeometryField`. This is encouraged instead of deprecated `GeoModelAdmin` and `OSMGeoAdmin`.

#### `django.contrib.postgres`

- The PostgreSQL backend now supports connecting by a service name. See PostgreSQL connection settings for more details.

- The new `AddConstraintNotValid` operation allows creating check constraints on PostgreSQL without verifying that all existing rows satisfy the new constraint.

- The new `ValidateConstraint` operation allows validating check constraints which were created using `AddConstraintNotValid` on PostgreSQL.

- The new `ArraySubquery()` expression allows using subqueries to construct lists of values on PostgreSQL.

- The new `trigram_word_similar` lookup, and the `TrigramWordDistance()` and `TrigramWordSimilarity()` expressions allow using trigram word similarity.

#### `django.contrib.staticfiles`

- `ManifestStaticFilesStorage` now replaces paths to JavaScript source map references with their hashed counterparts.

- The new `manifest_storage` argument of `ManifestFilesMixin` and `ManifestStaticFilesStorage` allows customizing the manifest file storage.

#### Cache

- The new async API for `django.core.cache.backends.base.BaseCache` begins the process of making cache backends async-compatible. The new async methods all have `a` prefixed names, e.g. `aadd()`, `aget()`, `aset()`, `aget_or_set()`, or `adelete_many()`.

  Going forward, the `a` prefix will be used for async variants of methods generally.

#### CSRF

- CSRF protection now consults the `Origin` header, if present. To facilitate this, some changes to the `CSRF_TRUSTED_ORIGINS` setting are required.

#### Forms

- `ModelChoiceField` now includes the provided value in the `params` argument of a raised `ValidationError` for the `invalid_choice` error message. This allows custom error messages to use the `%(value)s` placeholder.

- `BaseFormSet` now renders non-form errors with an additional class of `nonform` to help distinguish them from form-specific errors.

- `BaseFormSet` now allows customizing the widget used when deleting forms via `can_delete` by setting the `deletion_widget` attribute or overriding `get_deletion_widget()` method.

#### Internationalization

- Added support and translations for the Malay language.

#### Generic Views

- `DeleteView` now uses `FormMixin`, allowing you to provide a `Form` subclass, with a checkbox for example, to confirm deletion. In addition, this allows `DeleteView` to function with `django.contrib.messages.views.SuccessMessageMixin`.

  In accordance with `FormMixin`, object deletion for POST requests is handled in `form_valid()`. Custom delete logic in `delete()` handlers should be moved to `form_valid()`, or a shared helper method, as needed.

#### Logging

- The alias of the database used in an SQL call is now passed as extra context along with each message to the django.db.backends logger.

#### Management Commands

- The `runserver` management command now supports the `--skip-checks` option.

- On PostgreSQL, `dbshell` now supports specifying a password file.

- The `shell` command now respects `sys.__interactivehook__` at startup. This allows loading shell history between interactive sessions. As a consequence, `readline` is no longer loaded if running in isolated mode.

- The new `BaseCommand.suppressed_base_arguments` attribute allows suppressing unsupported default command options in the help output.

- The new `startapp --exclude` and `startproject --exclude` options allow excluding directories from the template.

#### Models

- New `QuerySet.contains(obj)` method returns whether the queryset contains the given object. This tries to perform the query in the simplest and fastest way possible.

- The new `precision` argument of the `Round()` database function allows specifying the number of decimal places after rounding.

- `QuerySet.bulk_create()` now sets the primary key on objects when using SQLite 3.35+.

- `DurationField` now supports multiplying and dividing by scalar values on SQLite.

- `QuerySet.bulk_update()` now returns the number of objects updated.

- The new `Expression.empty_result_set_value` attribute allows specifying a value to return when the function is used over an empty result set.

- The `skip_locked` argument of `QuerySet.select_for_update()` is now allowed on MariaDB 10.6+.

- `Lookup` expressions may now be used in `QuerySet` annotations, aggregations, and directly in filters.

- The new default argument for built-in aggregates allows specifying a value to be returned when the queryset (or grouping) contains no entries, rather than `None`.

#### Requests and Responses

- The `SecurityMiddleware` now adds the Cross-Origin Opener Policy header with a value of `'same-origin'` to prevent cross-origin popups from sharing the same browsing context. You can prevent this header from being added by setting the `SECURE_CROSS_ORIGIN_OPENER_POLICY` setting to `None`.

#### Signals

- The new `stdout` argument for `pre_migrate()` and `post_migrate()` signals allows redirecting output to a stream-like object. It should be preferred over `sys.stdout` and `print()` when emitting verbose output in order to allow proper capture when testing.

#### Templates

- `floatformat` template filter now allows using the `u` suffix to force disabling localization.

#### Tests

- The new `serialized_aliases` argument of `django.test.utils.setup_databases()` determines which `DATABASES` aliases test databases should have their state serialized to allow usage of the serialized_rollback feature.

- The `test --buffer` option now supports parallel tests.

- The new `logger` argument to `DiscoverRunner` allows a Python logger to be used for logging.

- The new `DiscoverRunner.log()` method provides a way to log messages that uses the `DiscoverRunner.logger`, or prints to the console if not set.

- `DiscoverRunner` can now execute tests in a random order using the `test --shuffle` option.

- The `test --parallel` option now supports the value `auto` to run one test process for each processor core.

- `TestCase.captureOnCommitCallbacks()` now captures new callbacks added while executing `transaction.on_commit()` callbacks.

## Backwards incompatible changes in 4.0

### Database backend API

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

- `DatabaseOperations.year_lookup_bounds_for_date_field()` and `year_lookup_bounds_for_datetime_field()` methods now take the optional `iso_year` argument in order to support bounds for ISO-8601 week-numbering years.

- The second argument of `DatabaseSchemaEditor._unique_sql()` and `_create_unique_sql()` methods is now `fields` instead of `columns`.

### `django.contrib.gis`

- Support for PostGIS 2.3 is removed.

- Support for GDAL 2.0 and GEOS 3.5 is removed.

### Dropped support for PostgreSQL 9.6

Upstream support for PostgreSQL 9.6 ends in November 2021. Django 4.0 supports PostgreSQL 10 and higher.

Also, the minimum supported version of `psycopg2` is increased from 2.5.4 to 2.8.4, as `psycopg2` 2.8.4 is the first release to support Python 3.8.

### Dropped support for Oracle 12.2 and 18c

Upstream support for Oracle 12.2 ends in March 2022 and for Oracle 18c it ends in June 2021. Django 3.2 will be supported until April 2024. Django 4.0 officially supports Oracle 19c.

### `CSRF_TRUSTED_ORIGINS` changes

#### Format change

Values in the `CSRF_TRUSTED_ORIGINS` setting must include the scheme (e.g. `'http://'` or `'https://'`) instead of only the hostname.

Also, values that started with a dot, must now also include an asterisk before the dot. For example, change `'.example.com'` to `'https://*.example.com'`.

A system check detects any required changes.

#### Configuring it may now be required

As CSRF protection now consults the `Origin` header, you may need to set `CSRF_TRUSTED_ORIGINS`, particularly if you allow requests from subdomains by setting `CSRF_COOKIE_DOMAIN` (or `SESSION_COOKIE_DOMAIN` if `CSRF_USE_SESSIONS` is enabled) to a value starting with a dot.

### `SecurityMiddleware` no longer sets the `X-XSS-Protection` header

The `SecurityMiddleware` no longer sets the `X-XSS-Protection` header if the `SECURE_BROWSER_XSS_FILTER` setting is `True`. The setting is removed.

Most modern browsers don’t honor the `X-XSS-Protection` HTTP header. You can use Content-Security-Policy without allowing `'unsafe-inline'` scripts instead.

If you want to support legacy browsers and set the header, use this line in a custom middleware:

    response.headers.setdefault("X-XSS-Protection", "1; mode=block")

### Migrations autodetector changes

The migrations autodetector now uses model states instead of model classes. Also, migration operations for `ForeignKey` and `ManyToManyField` fields no longer specify attributes which were not passed to the fields during initialization.

As a side-effect, running `makemigrations` might generate no-op `AlterField` operations for `ManyToManyField` and `ForeignKey` fields in some cases.

### `DeleteView` changes

`DeleteView` now uses `FormMixin` to handle POST requests. As a consequence, any custom deletion logic in `delete()` handlers should be moved to `form_valid()`, or a shared helper method, if required.

### Table and column naming scheme changes on Oracle

Django 4.0 inadvertently changed the table and column naming scheme on Oracle. This causes errors for models and fields with names longer than 30 characters. Unfortunately, renaming some Oracle tables and columns is required. Use the upgrade script in 33789 to generate `RENAME` statements to change naming scheme.

### Miscellaneous

- Support for `cx_Oracle` < 7.0 is removed.

- To allow serving a Django site on a subpath without changing the value of `STATIC_URL`, the leading slash is removed from that setting (now `'static/'`) in the default `startproject` template.

- The `AdminSite` method for the admin `index` view is no longer decorated with `never_cache` when accessed directly, rather than via the recommended `AdminSite.urls` property, or `AdminSite.get_urls()` method.

- Unsupported operations on a sliced queryset now raise `TypeError` instead of `AssertionError`.

- The undocumented `django.test.runner.reorder_suite()` function is renamed to `reorder_tests()`. It now accepts an iterable of tests rather than a test suite, and returns an iterator of tests.

- Calling `FileSystemStorage.delete()` with an empty `name` now raises `ValueError` instead of `AssertionError`.

- Calling `EmailMultiAlternatives.attach_alternative()` or `EmailMessage.attach()` with an invalid `content` or `mimetype` arguments now raise `ValueError` instead of `AssertionError`.

- `assertHTMLEqual()` no longer considers a non-boolean attribute without a value equal to an attribute with the same name and value.

- Tests that fail to load, for example due to syntax errors, now always match when using `test --tag`.

- The undocumented `django.contrib.admin.utils.lookup_needs_distinct()` function is renamed to `lookup_spawns_duplicates()`.

- The undocumented `HttpRequest.get_raw_uri()` method is removed. The `HttpRequest.build_absolute_uri()` method may be a suitable alternative.

- The `object` argument of undocumented `ModelAdmin.log_addition()`, `log_change()`, and `log_deletion()` methods is renamed to `obj`.

- `RssFeed`, `Atom1Feed`, and their subclasses now emit elements with no content as self-closing tags.

- `NodeList.render()` no longer casts the output of `render()` method for individual nodes to a string. `Node.render()` should always return a string as documented.

- The `where_class` property of `django.db.models.sql.query.Query` and the `where_class` argument to the private `get_extra_restriction()` method of `ForeignObject` and `ForeignObjectRel` are removed. If needed, initialize `django.db.models.sql.where.WhereNode` instead.

- The `filter_clause` argument of the undocumented `Query.add_filter()` method is replaced by two positional arguments `filter_lhs` and `filter_rhs`.

- `CsrfViewMiddleware` now uses `request.META['CSRF_COOKIE_NEEDS_UPDATE']` in place of `request.META['CSRF_COOKIE_USED']`, `request.csrf_cookie_needs_reset`, and `response.csrf_cookie_set` to track whether the CSRF cookie should be sent. This is an undocumented, private API.

- The undocumented `TRANSLATOR_COMMENT_MARK` constant is moved from `django.template.base` to `django.utils.translation.template`.

- The `real_apps` argument of the undocumented `django.db.migrations.state.ProjectState.__init__()` method must now be a set if provided.

- `RadioSelect` and `CheckboxSelectMultiple` widgets are now rendered in `<div>` tags so they are announced more concisely by screen readers. If you need the previous behavior, override the widget template with the appropriate template from Django 3.2.

- The `floatformat` template filter no longer depends on the `USE_L10N` setting and always returns localized output. Use the `u` suffix to disable localization.

- The default value of the `USE_L10N` setting is changed to `True`. See the Localization section above for more details.

- As part of the move to zoneinfo, `django.utils.timezone.utc` is changed to alias `datetime.timezone.utc`.

- The minimum supported version of `asgiref` is increased from 3.3.2 to 3.4.1.

## Features deprecated in 4.0

### Use of `pytz` time zones

As part of the move to zoneinfo, use of `pytz` time zones is deprecated.

Accordingly, the `is_dst` arguments to the following are also deprecated:

- `django.db.models.query.QuerySet.datetimes()`

- `django.db.models.functions.Trunc()`

- `django.db.models.functions.TruncSecond()`

- `django.db.models.functions.TruncMinute()`

- `django.db.models.functions.TruncHour()`

- `django.db.models.functions.TruncDay()`

- `django.db.models.functions.TruncWeek()`

- `django.db.models.functions.TruncMonth()`

- `django.db.models.functions.TruncQuarter()`

- `django.db.models.functions.TruncYear()`

- `django.utils.timezone.make_aware()`

Support for use of `pytz` will be removed in Django 5.0.

### Time zone support

In order to follow good practice, the default value of the `USE_TZ` setting will change from `False` to `True`, and time zone support will be enabled by default, in Django 5.0.

Note that the default `settings.py` file created by `django-admin startproject` includes `USE_TZ = True` since Django 1.4.

You can set `USE_TZ` to `False` in your project settings before then to opt-out.

### Localization

In order to follow good practice, the default value of the `USE_L10N` setting is changed from `False` to `True`.

Moreover `USE_L10N` is deprecated as of this release. Starting with Django 5.0, by default, any date or number displayed by Django will be localized.

The `{% localize %}` tag and the `localize`/ `unlocalize` filters will still be honored by Django.

### Miscellaneous

- `SERIALIZE` test setting is deprecated as it can be inferred from the `databases` with the serialized_rollback option enabled.

- The undocumented `django.utils.baseconv` module is deprecated.

- The undocumented `django.utils.datetime_safe` module is deprecated.

- The default sitemap protocol for sitemaps built outside the context of a request will change from `'http'` to `'https'` in Django 5.0.

- The `extra_tests` argument for `DiscoverRunner.build_suite()` and `DiscoverRunner.run_tests()` is deprecated.

- The `ArrayAgg`, `JSONBAgg`, and `StringAgg` aggregates will return `None` when there are no rows instead of `[]`, `[]`, and `''` respectively in Django 5.0. If you need the previous behavior, explicitly set `default` to `Value([])`, `Value('[]')`, or `Value('')`.

- The `django.contrib.gis.admin.GeoModelAdmin` and `OSMGeoAdmin` classes are deprecated. Use `ModelAdmin` and `GISModelAdmin` instead.

- Since form rendering now uses the template engine, the undocumented `BaseForm._html_output()` helper method is deprecated.

- The ability to return a `str` from `ErrorList` and `ErrorDict` is deprecated. It is expected these methods return a `SafeString`.

## Features removed in 4.0

These features have reached the end of their deprecation cycle and are removed in Django 4.0.

See Features deprecated in 3.0 for details on these changes, including how to remove usage of these features.

- `django.utils.http.urlquote()`, `urlquote_plus()`, `urlunquote()`, and `urlunquote_plus()` are removed.

- `django.utils.encoding.force_text()` and `smart_text()` are removed.

- `django.utils.translation.ugettext()`, `ugettext_lazy()`, `ugettext_noop()`, `ungettext()`, and `ungettext_lazy()` are removed.

- `django.views.i18n.set_language()` doesn’t set the user language in `request.session` (key `_language`).

- `alias=None` is required in the signature of `django.db.models.Expression.get_group_by_cols()` subclasses.

- `django.utils.text.unescape_entities()` is removed.

- `django.utils.http.is_safe_url()` is removed.

See Features deprecated in 3.1 for details on these changes, including how to remove usage of these features.

- The `PASSWORD_RESET_TIMEOUT_DAYS` setting is removed.

- The `isnull` lookup no longer allows using non-boolean values as the right-hand side.

- The `django.db.models.query_utils.InvalidQuery` exception class is removed.

- The `django-admin.py` entry point is removed.

- The `HttpRequest.is_ajax()` method is removed.

- Support for the pre-Django 3.1 encoding format of cookies values used by `django.contrib.messages.storage.cookie.CookieStorage` is removed.

- Support for the pre-Django 3.1 password reset tokens in the admin site (that use the SHA-1 hashing algorithm) is removed.

- Support for the pre-Django 3.1 encoding format of sessions is removed.

- Support for the pre-Django 3.1 `django.core.signing.Signer` signatures (encoded with the SHA-1 algorithm) is removed.

- Support for the pre-Django 3.1 `django.core.signing.dumps()` signatures (encoded with the SHA-1 algorithm) in `django.core.signing.loads()` is removed.

- Support for the pre-Django 3.1 user sessions (that use the SHA-1 algorithm) is removed.

- The `get_response` argument for `django.utils.deprecation.MiddlewareMixin.__init__()` is required and doesn’t accept `None`.

- The `providing_args` argument for `django.dispatch.Signal` is removed.

- The `length` argument for `django.utils.crypto.get_random_string()` is required.

- The `list` message for `ModelMultipleChoiceField` is removed.

- Support for passing raw column aliases to `QuerySet.order_by()` is removed.

- The `NullBooleanField` model field is removed, except for support in historical migrations.

- `django.conf.urls.url()` is removed.

- The `django.contrib.postgres.fields.JSONField` model field is removed, except for support in historical migrations.

- `django.contrib.postgres.fields.jsonb.KeyTransform` and `django.contrib.postgres.fields.jsonb.KeyTextTransform` are removed.

- `django.contrib.postgres.forms.JSONField` is removed.

- The `{% ifequal %}` and `{% ifnotequal %}` template tags are removed.

- The `DEFAULT_HASHING_ALGORITHM` transitional setting is removed.