django1/docs/releases/1.4-alpha-1.txt

==============================
Django 1.4 alpha release notes
==============================

December 22, 2011.

Welcome to Django 1.4 alpha!

This is the first in a series of preview/development releases leading up to the
eventual release of Django 1.4, scheduled for March 2012. This release is
primarily targeted at developers who are interested in trying out new features
and testing the Django codebase to help identify and resolve bugs prior to the
final 1.4 release.

As such, this release is *not* intended for production use, and any such use is
discouraged.

Django 1.4 alpha includes various `new features`_ and some minor `backwards
incompatible changes`_. There are also some features that have been dropped,
which are detailed in :doc:`our deprecation plan </internals/deprecation>`, and
we've `begun the deprecation process for some features`_.

.. _new features: `What's new in Django 1.4`_
.. _backwards incompatible changes: `Backwards incompatible changes in 1.4`_
.. _begun the deprecation process for some features: `Features deprecated in 1.4`_

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

While not a new feature, it's important to note that Django 1.4 introduces the
second shift in our Python compatibility policy since Django's initial public
debut. Django 1.2 dropped support for Python 2.3; now Django 1.4 drops support
for Python 2.4. As such, the minimum Python version required for Django is now
2.5, and Django is tested and supported on Python 2.5, 2.6 and 2.7.

This change should affect only a small number of Django users, as most
operating-system vendors today are shipping Python 2.5 or newer as their default
version. If you're still using Python 2.4, however, you'll need to stick to
Django 1.3 until you can upgrade; per :doc:`our support policy
</internals/release-process>`, Django 1.3 will continue to receive security
support until the release of Django 1.5.

Django does not support Python 3.x at this time. A document outlining our full
timeline for deprecating Python 2.x and moving to Python 3.x will be published
before the release of Django 1.4.

What's new in Django 1.4
========================

Support for in-browser testing frameworks
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Django 1.4 now supports the integration with in-browser testing frameworks such
as Selenium_ or Windmill_ thanks to the :class:`django.test.LiveServerTestCase`
base class, allowing you to test the interactions between your site's front and
back ends more comprehensively. See the
:class:`documentation<django.test.LiveServerTestCase>` for more details and
concrete examples.

.. _Windmill: http://www.getwindmill.com/
.. _Selenium: http://seleniumhq.org/

``SELECT FOR UPDATE`` support
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Django 1.4 now includes a :meth:`QuerySet.select_for_update()
<django.db.models.query.QuerySet.select_for_update>` method which generates a
``SELECT ... FOR UPDATE`` SQL query. This will lock rows until the end of the
transaction, meaning that other transactions cannot modify or delete rows
matched by a ``FOR UPDATE`` query.

For more details, see the documentation for
:meth:`~django.db.models.query.QuerySet.select_for_update`.

``Model.objects.bulk_create`` in the ORM
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

This method allows for more efficient creation of multiple objects in the ORM.
It can provide significant performance increases if you have many objects.
Django makes use of this internally, meaning some operations (such as database
setup for test suites) have seen a performance benefit as a result.

See the :meth:`~django.db.models.query.QuerySet.bulk_create` docs for more
information.

``QuerySet.prefetch_related``
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Similar to :meth:`~django.db.models.query.QuerySet.select_related` but with a
different strategy and broader scope,
:meth:`~django.db.models.query.QuerySet.prefetch_related` has been added to
:class:`~django.db.models.query.QuerySet`. This method returns a new
``QuerySet`` that will prefetch in a single batch each of the specified related
lookups as soon as it begins to be evaluated. Unlike ``select_related``, it does
the joins in Python, not in the database, and supports many-to-many
relationships, :class:`~django.contrib.contenttypes.generic.GenericForeignKey`
and more. This enables you to fix many instances of a very common performance
problem, in which your code ends up doing O(n) database queries (or worse) if
objects on your primary ``QuerySet`` each have many related objects that you
also need.

HTML5
~~~~~

We've switched the admin and other bundled templates to use the HTML5
doctype. While Django will be careful in its use of HTML5 features, to maintain
compatibility with older browsers, this change means that you can use any HTML5
features you need in admin pages without having to lose HTML validity or
override the provided templates to change the doctype.

List filters in admin interface
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Prior to Django 1.4, the Django admin app allowed specifying change list
filters by specifying a field lookup (including spanning relations), and
not custom filters. This has been rectified with a simple API previously
known as "FilterSpec" which was used internally. For more details, see the
documentation for :attr:`~django.contrib.admin.ModelAdmin.list_filter`.

Multiple sort in admin interface
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The admin change list now supports sorting on multiple columns. It respects
all elements of the :attr:`~django.contrib.admin.ModelAdmin.ordering`
attribute, and sorting on multiple columns by clicking on headers is designed
to work similarly to how desktop GUIs do it. The new hook
:meth:`~django.contrib.admin.ModelAdmin.get_ordering` for specifying the
ordering dynamically (e.g. depending on the request) has also been added.

New ``ModelAdmin`` methods
~~~~~~~~~~~~~~~~~~~~~~~~~~

A new :meth:`~django.contrib.admin.ModelAdmin.save_related` method was added to
:mod:`~django.contrib.admin.ModelAdmin` to ease the customization of how
related objects are saved in the admin.

Two other new methods,
:meth:`~django.contrib.admin.ModelAdmin.get_list_display` and
:meth:`~django.contrib.admin.ModelAdmin.get_list_display_links`
were added to :class:`~django.contrib.admin.ModelAdmin` to enable the dynamic
customization of fields and links to display on the admin
change list.

Admin inlines respect user permissions
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Admin inlines will now only allow those actions for which the user has
permission. For ``ManyToMany`` relationships with an auto-created intermediate
model (which does not have its own permissions), the change permission for the
related model determines if the user has the permission to add, change or
delete relationships.

Tools for cryptographic signing
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Django 1.4 adds both a low-level API for signing values and a high-level API
for setting and reading signed cookies, one of the most common uses of
signing in Web applications.

See :doc:`cryptographic signing </topics/signing>` docs for more information.

Cookie-based session backend
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Django 1.4 introduces a new cookie based backend for the session framework
which uses the tools for :doc:`cryptographic signing </topics/signing>` to
store the session data in the client's browser.

See the :ref:`cookie-based backend <cookie-session-backend>` docs for
more information.

New form wizard
~~~~~~~~~~~~~~~

The previously shipped ``FormWizard`` of the formtools contrib app has been
replaced with a new implementation that is based on the class based views
introduced in Django 1.3. It features a pluggable storage API and doesn't
require the wizard to pass around hidden fields for every previous step.

Django 1.4 ships with a session based storage backend and a cookie based
storage backend. The latter uses the tools for
:doc:`cryptographic signing </topics/signing>` also introduced in
Django 1.4 to store the wizard state in the user's cookies.

See the :doc:`form wizard </ref/contrib/formtools/form-wizard>` docs for
more information.

``reverse_lazy``
~~~~~~~~~~~~~~~~

A lazily evaluated version of :func:`django.core.urlresolvers.reverse` was
added to allow using URL reversals before the project's URLConf gets loaded.

Translating URL patterns
~~~~~~~~~~~~~~~~~~~~~~~~

Django 1.4 gained the ability to look for a language prefix in the URL pattern
when using the new :func:`django.conf.urls.i18n.i18n_patterns` helper function.
Additionally, it's now possible to define translatable URL patterns using
:func:`~django.utils.translation.ugettext_lazy`. See
:ref:`url-internationalization` for more information about the language prefix
and how to internationalize URL patterns.

Contextual translation support for ``{% trans %}`` and ``{% blocktrans %}``
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Django 1.3 introduced :ref:`contextual translation<contextual-markers>` support
in Python files via the ``pgettext`` function. This is now also supported by
the :ttag:`trans` and :ttag:`blocktrans` template tags using the new
``context`` keyword.

Customizable ``SingleObjectMixin`` URLConf kwargs
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Two new attributes,
:attr:`pk_url_kwarg<django.views.generic.detail.SingleObjectMixin.pk_url_kwarg>` and
:attr:`slug_url_kwarg<django.views.generic.detail.SingleObjectMixin.slug_url_kwarg>`,
have been added to :class:`django.views.generic.detail.SingleObjectMixin` to
enable the customization of URLConf keyword arguments used for single
object generic views.

Assignment template tags
~~~~~~~~~~~~~~~~~~~~~~~~

A new helper function,
:ref:`assignment_tag<howto-custom-template-tags-assignment-tags>`, was added to
``template.Library`` to ease the creation of template tags that store some
data in a specified context variable.

``*args`` and ``**kwargs`` support for template tag helper functions
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

:ref:`simple_tag<howto-custom-template-tags-simple-tags>`, :ref:`inclusion_tag
<howto-custom-template-tags-inclusion-tags>` and the newly introduced
:ref:`assignment_tag<howto-custom-template-tags-assignment-tags>` template
helper functions may now accept any number of positional or keyword arguments.
For example:

.. code-block:: python

    @register.simple_tag
    def my_tag(a, b, *args, **kwargs):
        warning = kwargs['warning']
        profile = kwargs['profile']
        ...
        return ...

Then in the template any number of arguments may be passed to the template tag.
For example:

.. code-block:: html+django

    {% my_tag 123 "abcd" book.title warning=message|lower profile=user.profile %}

No wrapping of exceptions in ``TEMPLATE_DEBUG`` mode
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

In previous versions of Django, whenever the :setting:`TEMPLATE_DEBUG` setting
was ``True``, any exception raised during template rendering (even exceptions
unrelated to template syntax) were wrapped in ``TemplateSyntaxError`` and
re-raised. This was done in order to provide detailed template source location
information in the debug 500 page.

In Django 1.4, exceptions are no longer wrapped. Instead, the original
exception is annotated with the source information. This means that catching
exceptions from template rendering is now consistent regardless of the value of
:setting:`TEMPLATE_DEBUG`, and there's no need to catch and unwrap
``TemplateSyntaxError`` in order to catch other errors.

``truncatechars`` template filter
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Added a filter which truncates a string to be no longer than the specified
number of characters. Truncated strings end with a translatable ellipsis
sequence ("..."). See the :tfilter:`truncatechars docs <truncatechars>` for
more details.

``static`` template tag
~~~~~~~~~~~~~~~~~~~~~~~

The :mod:`staticfiles<django.contrib.staticfiles>` contrib app has now a new
:ttag:`static template tag<staticfiles-static>` to refer to files saved with
the :setting:`STATICFILES_STORAGE` storage backend. It'll use the storage
``url`` method and therefore supports advanced features such as
:ref:`serving files from a cloud service<staticfiles-from-cdn>`.

``CachedStaticFilesStorage`` storage backend
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Additional to the `static template tag`_ the
:mod:`staticfiles<django.contrib.staticfiles>` contrib app now has a
:class:`~django.contrib.staticfiles.storage.CachedStaticFilesStorage` which
caches the files it saves (when running the :djadmin:`collectstatic`
management command) by appending the MD5 hash of the file's content to the
filename. For example, the file ``css/styles.css`` would also be saved as
``css/styles.55e7cbb9ba48.css``

See the :class:`~django.contrib.staticfiles.storage.CachedStaticFilesStorage`
docs for more information.

Simple clickjacking protection
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We've added a middleware to provide easy protection against `clickjacking
<http://en.wikipedia.org/wiki/Clickjacking>`_ using the X-Frame-Options
header. It's not enabled by default for backwards compatibility reasons, but
you'll almost certainly want to :doc:`enable it </ref/clickjacking/>` to help
plug that security hole for browsers that support the header.

CSRF improvements
~~~~~~~~~~~~~~~~~

We've made various improvements to our CSRF features, including the
:func:`~django.views.decorators.csrf.ensure_csrf_cookie` decorator which can
help with AJAX heavy sites, protection for PUT and DELETE, and settings
:setting:`CSRF_COOKIE_SECURE` and :setting:`CSRF_COOKIE_PATH` which can improve
the security and usefulness of the CSRF protection. See the :doc:`CSRF docs
</ref/contrib/csrf>` for more information.

Error report filtering
~~~~~~~~~~~~~~~~~~~~~~

Two new function decorators, :func:`sensitive_variables` and
:func:`sensitive_post_parameters`, were added to allow designating the
traceback frames' local variables and request's POST parameters susceptible
to contain sensitive information and that should be filtered out of error
reports.

All POST parameters are now systematically filtered out of error reports for
certain :mod:`contrib.views.auth` views (``login``, ``password_reset_confirm``,
``password_change``, and ``add_view`` and ``user_change_password`` in the
``auth`` admin) to prevent the leaking of sensitive information such as user
passwords.

You may override or customize the default filtering by writing a
:ref:`custom filter<custom-error-reports>`. Learn more on
:ref:`Filtering error reports<filtering-error-reports>`.

Extended IPv6 support
~~~~~~~~~~~~~~~~~~~~~

The previously added support for IPv6 addresses when using the runserver
management command in Django 1.3 has now been further extended by adding
a :class:`~django.db.models.fields.GenericIPAddressField` model field,
a :class:`~django.forms.fields.GenericIPAddressField` form field and
the validators :data:`~django.core.validators.validate_ipv46_address` and
:data:`~django.core.validators.validate_ipv6_address`

Updated default project layout and ``manage.py``
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Django 1.4 ships with an updated default project layout and ``manage.py`` file
for the :djadmin:`startproject` management command. These fix some issues with
the previous ``manage.py`` handling of Python import paths that caused double
imports, trouble moving from development to deployment, and other
difficult-to-debug path issues.

The previous ``manage.py`` calls functions that are now deprecated, and thus
projects upgrading to Django 1.4 should update their ``manage.py``. (The
old-style ``manage.py`` will continue to work as before until Django 1.6; in
1.5 it will raise ``DeprecationWarning``).

The new recommended ``manage.py`` file should look like this::

    #!/usr/bin/env python
    import os, sys

    if __name__ == "__main__":
        os.environ.setdefault("DJANGO_SETTINGS_MODULE", "{{ project_name }}.settings")

        from django.core.management import execute_from_command_line

        execute_from_command_line(sys.argv)

``{{ project_name }}`` should be replaced with the Python package name of the
actual project.

If settings, URLconf, and apps within the project are imported or referenced
using the project-name prefix (e.g. ``myproject.settings``, ``ROOT_URLCONF =
"myproject.urls"``, etc), the new ``manage.py`` will need to be moved one
directory up, so it is outside the project package rather than adjacent to
``settings.py`` and ``urls.py``.

For instance, with the following layout::

    manage.py
    mysite/
        __init__.py
        settings.py
        urls.py
        myapp/
            __init__.py
            models.py

You could import ``mysite.settings``, ``mysite.urls``, and ``mysite.myapp``,
but not ``settings``, ``urls``, or ``myapp`` as top-level modules.

Anything imported as a top-level module can be placed adjacent to the new
``manage.py``. For instance, to decouple "myapp" from the project module and
import it as just ``myapp``, place it outside the ``mysite/`` directory::

    manage.py
    myapp/
        __init__.py
        models.py
    mysite/
        __init__.py
        settings.py
        urls.py

If the same code is imported inconsistently (some places with the project
prefix, some places without it), the imports will need to be cleaned up when
switching to the new ``manage.py``.

Improved WSGI support
~~~~~~~~~~~~~~~~~~~~~

The :djadmin:`startproject` management command now adds a :file:`wsgi.py`
module to the initial project layout, containing a simple WSGI application that
can be used for :doc:`deploying with WSGI app
servers</howto/deployment/wsgi/index>`.

The :djadmin:`built-in development server<runserver>` now supports using an
externally-defined WSGI callable, so as to make it possible to run runserver
with the same WSGI configuration that is used for deployment. A new
:setting:`WSGI_APPLICATION` setting is available to configure which WSGI
callable :djadmin:`runserver` uses.

(The :djadmin:`runfcgi` management command also internally wraps the WSGI
callable configured via :setting:`WSGI_APPLICATION`.)

Support for time zones
~~~~~~~~~~~~~~~~~~~~~~

Django 1.4 adds :ref:`support for time zones <time-zones>`. When it's enabled,
Django stores date and time information in UTC in the database, uses time
zone-aware datetime objects internally, and translates them to the end user's
time zone in templates and forms.

Reasons for using this feature include:

- Customizing date and time display for users around the world.
- Storing datetimes in UTC for database portability and interoperability.
  (This argument doesn't apply to PostgreSQL, because it already stores
  timestamps with time zone information in Django 1.3.)
- Avoiding data corruption problems around DST transitions.

Time zone support in enabled by default in new projects created with
:djadmin:`startproject`. If you want to use this feature in an existing
project, there is a :ref:`migration guide <time-zones-migration-guide>`.

Minor features
~~~~~~~~~~~~~~

Django 1.4 also includes several smaller improvements worth noting:

* A more usable stacktrace in the technical 500 page: frames in the
  stack trace which reference Django's code are dimmed out, while
  frames in user code are slightly emphasized. This change makes it
  easier to scan a stacktrace for issues in user code.

* :doc:`Tablespace support </topics/db/tablespaces>` in PostgreSQL.

* Customizable names for :meth:`~django.template.Library.simple_tag`.

* In the documentation, a helpful :doc:`security overview </topics/security>`
  page.

* Function :func:`django.contrib.auth.models.check_password` has been moved
  to the :mod:`django.contrib.auth.utils` module. Importing it from the old
  location will still work, but you should update your imports.

* The :djadmin:`collectstatic` management command gained a ``--clear`` option
  to delete all files at the destination before copying or linking the static
  files.

* It is now possible to load fixtures containing forward references when using
  MySQL with the InnoDB database engine.

* A new 403 response handler has been added as
  ``'django.views.defaults.permission_denied'``. You can set your own handler by
  setting the value of :data:`django.conf.urls.handler403`. See the
  documentation about :ref:`the 403 (HTTP Forbidden) view<http_forbidden_view>`
  for more information.

* The :ttag:`trans` template tag now takes an optional ``as`` argument to
  be able to retrieve a translation string without displaying it but setting
  a template context variable instead.

* The :ttag:`if` template tag now supports ``{% elif %}`` clauses.

* A new plain text version of the HTTP 500 status code internal error page
  served when :setting:`DEBUG` is ``True`` is now sent to the client when
  Django detects that the request has originated in JavaScript code
  (:meth:`~django.http.HttpRequest.is_ajax` is used for this).

  Similarly to its HTML counterpart, it contains a collection of different
  pieces of information about the state of the web application.

  This should make it easier to read when debugging interaction with
  client-side Javascript code.

* Added the :djadminopt:`--no-location` option to the :djadmin:`makemessages`
  command.

* Changed the ``locmem`` cache backend to use
  ``pickle.HIGHEST_PROTOCOL`` for better compatibility with the other
  cache backends.

Backwards incompatible changes in 1.4
=====================================

django.contrib.admin
~~~~~~~~~~~~~~~~~~~~

The included administration app ``django.contrib.admin`` has for a long time
shipped with a default set of static files such as JavaScript, images and
stylesheets. Django 1.3 added a new contrib app ``django.contrib.staticfiles``
to handle such files in a generic way and defined conventions for static
files included in apps.

Starting in Django 1.4 the admin's static files are now also following this
convention to make it easier to deploy the included files. In previous
versions of Django, it was also common to define a ``ADMIN_MEDIA_PREFIX``
setting to point to the URL where the admin's static files are served by a
web server. This setting has now been deprecated and replaced by the more
general setting :setting:`STATIC_URL`. Django will now expect to find the
admin static files under the URL ``<STATIC_URL>/admin/``.

If you've previously used a URL path for ``ADMIN_MEDIA_PREFIX`` (e.g.
``/media/``) simply make sure :setting:`STATIC_URL` and :setting:`STATIC_ROOT`
are configured and your web server serves the files correctly. The development
server continues to serve the admin files just like before. Don't hesitate to
consult the :doc:`static files howto </howto/static-files>` for further
details.

In case your ``ADMIN_MEDIA_PREFIX`` is set to an own domain (e.g.
``http://media.example.com/admin/``) make sure to also set your
:setting:`STATIC_URL` setting to the correct URL, for example
``http://media.example.com/``.

.. warning::

    If you're implicitely relying on the path of the admin static files on
    your server's file system when you deploy your site, you have to update
    that path. The files were moved from :file:`django/contrib/admin/media/`
    to :file:`django/contrib/admin/static/admin/`.

Supported browsers for the admin
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Django hasn't had a clear policy on which browsers are supported for using the
admin app. Django's new policy formalizes existing practices: `YUI's A-grade`_
browsers should provide a fully-functional admin experience, with the notable
exception of IE6, which is no longer supported.

Released over ten years ago, IE6 imposes many limitations on modern web
development. The practical implications of this policy are that contributors
are free to improve the admin without consideration for these limitations.

This new policy **has no impact** on development outside of the admin. Users of
Django are free to develop webapps compatible with any range of browsers.

.. _YUI's A-grade: http://yuilibrary.com/yui/docs/tutorials/gbs/

Removed admin icons
~~~~~~~~~~~~~~~~~~~

As part of an effort to improve the performance and usability of the admin's
changelist sorting interface and of the admin's :attr:`horizontal
<django.contrib.admin.ModelAdmin.filter_horizontal>` and :attr:`vertical
<django.contrib.admin.ModelAdmin.filter_vertical>` "filter" widgets, some icon
files were removed and grouped into two sprite files, respectively:
``selector-add.gif``, ``selector-addall.gif``, ``selector-remove.gif``,
``selector-removeall.gif``, ``selector_stacked-add.gif`` and
``selector_stacked-remove.gif`` into ``selector-icons.gif``; and
``arrow-up.gif`` and ``arrow-down.gif`` into ``sorting-icons.gif``. If you used
those icons to customize the admin then you will want to replace them with your
own icons or retrieve them from a previous release.

CSS class names in admin forms
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

To avoid conflicts with other common CSS class names (e.g. "button"), a prefix
"field-" has been added to all CSS class names automatically generated from the
form field names in the main admin forms, stacked inline forms and tabular
inline cells. You will need to take that prefix into account in your custom
style sheets or javascript files if you previously used plain field names as
selectors for custom styles or javascript transformations.

Compatibility with old signed data
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Django 1.3 changed the cryptographic signing mechanisms used in a number of
places in Django. While Django 1.3 kept fallbacks that would accept hashes
produced by the previous methods, these fallbacks are removed in Django 1.4.

So, if you upgrade to Django 1.4 directly from 1.2 or earlier, you may
lose/invalidate certain pieces of data that have been cryptographically signed
using an old method. To avoid this, use Django 1.3 first, for a period of time,
to allow the signed data to expire naturally. The affected parts are detailed
below, with 1) the consequences of ignoring this advice and 2) the amount of
time you need to run Django 1.3 for the data to expire or become irrelevant.

* contrib.sessions data integrity check

  * consequences: the user will be logged out, and session data will be lost.

  * time period: defined by SESSION_COOKIE_AGE.

* contrib.auth password reset hash

  * consequences: password reset links from before the upgrade will not work.

  * time period: defined by PASSWORD_RESET_TIMEOUT_DAYS.

Form related hashes — these are much shorter lifetime, and are relevant only for
the short window where a user might fill in a form generated by the pre-upgrade
Django instance, and try to submit it to the upgraded Django instance:

* contrib.comments form security hash

  * consequences: the user will see a validation error "Security hash failed".

  * time period: the amount of time you expect users to take filling out comment
    forms.

* FormWizard security hash

  * consequences: the user will see an error about the form having expired,
    and will be sent back to the first page of the wizard, losing the data
    they have inputted so far.

  * time period: the amount of time you expect users to take filling out the
    affected forms.

* CSRF check

  * Note: This is actually a Django 1.1 fallback, not Django 1.2,
    and applies only if you are upgrading from 1.1.

  * consequences: the user will see a 403 error with any CSRF protected POST
    form.

  * time period: the amount of time you expect user to take filling out
    such forms.

django.contrib.flatpages
~~~~~~~~~~~~~~~~~~~~~~~~

Starting in the 1.4 release the
:class:`~django.contrib.flatpages.middleware.FlatpageFallbackMiddleware` only
adds a trailing slash and redirects if the resulting URL refers to an existing
flatpage. For example, requesting ``/notaflatpageoravalidurl`` in a previous
version would redirect to ``/notaflatpageoravalidurl/``, which would
subsequently raise a 404. Requesting ``/notaflatpageoravalidurl`` now will
immediately raise a 404. Additionally redirects returned by flatpages are now
permanent (301 status code) to match the behavior of the
:class:`~django.middleware.common.CommonMiddleware`.

Serialization of :class:`~datetime.datetime` and :class:`~datetime.time`
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

As a consequence of time zone support, and according to the ECMA-262
specification, some changes were made to the JSON serializer:

- It includes the time zone for aware datetime objects. It raises an exception
  for aware time objects.
- It includes milliseconds for datetime and time objects. There is still
  some precision loss, because Python stores microseconds (6 digits) and JSON
  only supports milliseconds (3 digits). However, it's better than discarding
  microseconds entirely.

The XML serializer was also changed to use ISO8601 for datetimes. The letter
``T`` is used to separate the date part from the time part, instead of a
space. Time zone information is included in the ``[+-]HH:MM`` format.

The serializers will dump datetimes in fixtures with these new formats. They
can still load fixtures that use the old format.

``supports_timezone`` changed to ``False`` for SQLite
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The database feature ``supports_timezone`` used to be ``True`` for SQLite.
Indeed, if you saved an aware datetime object, SQLite stored a string that
included an UTC offset. However, this offset was ignored when loading the value
back from the database, which could corrupt the data.

In the context of time zone support, this flag was changed to ``False``, and
datetimes are now stored without time zone information in SQLite. When
:setting:`USE_TZ` is ``False``, if you attempt to save an aware datetime
object, Django raises an exception.

Database connection's thread-locality
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

``DatabaseWrapper`` objects (i.e. the connection objects referenced by
``django.db.connection`` and ``django.db.connections["some_alias"]``) used to
be thread-local. They are now global objects in order to be potentially shared
between multiple threads. While the individual connection objects are now
global, the ``django.db.connections`` dictionary referencing those objects is
still thread-local. Therefore if you just use the ORM or
``DatabaseWrapper.cursor()`` then the behavior is still the same as before.
Note, however, that ``django.db.connection`` does not directly reference the
default ``DatabaseWrapper`` object any more and is now a proxy to access that
object's attributes. If you need to access the actual ``DatabaseWrapper``
object, use ``django.db.connections[DEFAULT_DB_ALIAS]`` instead.

As part of this change, all underlying SQLite connections are now enabled for
potential thread-sharing (by passing the ``check_same_thread=False`` attribute
to pysqlite). ``DatabaseWrapper`` however preserves the previous behavior by
disabling thread-sharing by default, so this does not affect any existing
code that purely relies on the ORM or on ``DatabaseWrapper.cursor()``.

Finally, while it is now possible to pass connections between threads, Django
does not make any effort to synchronize access to the underlying backend.
Concurrency behavior is defined by the underlying backend implementation.
Check their documentation for details.

`COMMENTS_BANNED_USERS_GROUP` setting
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Django's :doc:`comments app </ref/contrib/comments/index>` has historically
supported excluding the comments of a special user group, but we've never
documented the feature properly and didn't enforce the exclusion in other parts
of the app, e.g., the template tags. To fix this problem, we removed the code
from the feed class.

If you rely on the feature and want to restore the old behavior, simply use
a custom comment model manager to exclude the user group, like this::

    from django.conf import settings
    from django.contrib.comments.managers import CommentManager

    class BanningCommentManager(CommentManager):
        def get_query_set(self):
            qs = super(BanningCommentManager, self).get_query_set()
            if getattr(settings, 'COMMENTS_BANNED_USERS_GROUP', None):
                where = ['user_id NOT IN (SELECT user_id FROM auth_user_groups WHERE group_id = %s)']
                params = [settings.COMMENTS_BANNED_USERS_GROUP]
                qs = qs.extra(where=where, params=params)
            return qs

Save this model manager in your custom comment app (e.g. in
``my_comments_app/managers.py``) and add it your
:ref:`custom comment app model <custom-comment-app-api>`::

    from django.db import models
    from django.contrib.comments.models import Comment

    from my_comments_app.managers import BanningCommentManager

    class CommentWithTitle(Comment):
        title = models.CharField(max_length=300)

        objects = BanningCommentManager()

For more details, see the documentation about
:doc:`customizing the comments framework </ref/contrib/comments/custom>`.

`IGNORABLE_404_STARTS` and `IGNORABLE_404_ENDS` settings
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Django can report 404 errors: see :doc:`/howto/error-reporting`.
Until Django 1.3, it was possible to exclude some URLs from the reporting
by adding prefixes to :setting:`IGNORABLE_404_STARTS` and suffixes to
:setting:`IGNORABLE_404_ENDS`.

In Django 1.4, these two settings are superseded by
:setting:`IGNORABLE_404_URLS`, which is a list of compiled regular expressions.
Django won't send an email for 404 errors on URLs that match any of them.

Furthermore, the previous settings had some rather arbitrary default values::

    IGNORABLE_404_STARTS = ('/cgi-bin/', '/_vti_bin', '/_vti_inf')
    IGNORABLE_404_ENDS = ('mail.pl', 'mailform.pl', 'mail.cgi', 'mailform.cgi',
                          'favicon.ico', '.php')

It's not Django's role to decide if your website has a legacy ``/cgi-bin/``
section or a ``favicon.ico``. As a consequence, the default values of
:setting:`IGNORABLE_404_URLS`, :setting:`IGNORABLE_404_STARTS` and
:setting:`IGNORABLE_404_ENDS` are all now empty.

If you have customized :setting:`IGNORABLE_404_STARTS` or
:setting:`IGNORABLE_404_ENDS`, or if you want to keep the old default value,
you should add the following lines in your settings file::

    import re
    IGNORABLE_404_URLS = (
        # for each <prefix> in IGNORABLE_404_STARTS
        re.compile(r'^<prefix>'),
        # for each <suffix> in IGNORABLE_404_ENDS
        re.compile(r'<suffix>$'),
    )

Don't forget to escape characters that have a special meaning in a regular
expression.

CSRF protection extended to PUT and DELETE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Previously, Django's :doc:`CSRF protection </ref/contrib/csrf/>` provided
protection against only POST requests. Since use of PUT and DELETE methods in
AJAX applications is becoming more common, we now protect all methods not
defined as safe by :rfc:`2616` i.e. we exempt GET, HEAD, OPTIONS and TRACE, and
enforce protection on everything else.

If you are using PUT or DELETE methods in AJAX applications, please see the
:ref:`instructions about using AJAX and CSRF <csrf-ajax>`.

``django.core.template_loaders``
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

This was an alias to ``django.template.loader`` since 2005, it has been removed
without emitting a warning due to the length of the deprecation. If your code
still referenced this please use ``django.template.loader`` instead.

``django.db.models.fields.URLField.verify_exists``
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

This functionality has been removed due to intractable performance and
security issues. Any existing usage of ``verify_exists`` should be
removed.

``django.core.files.storage.Storage.open``
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The ``open`` method of the base Storage class took an obscure parameter
``mixin`` which allowed you to dynamically change the base classes of the
returned file object. This has been removed. In the rare case you relied on the
`mixin` parameter, you can easily achieve the same by overriding the `open`
method, e.g.::

    from django.core.files import File
    from django.core.files.storage import FileSystemStorage

    class Spam(File):
        """
        Spam, spam, spam, spam and spam.
        """
        def ham(self):
            return 'eggs'

    class SpamStorage(FileSystemStorage):
        """
        A custom file storage backend.
        """
        def open(self, name, mode='rb'):
            return Spam(open(self.path(name), mode))

YAML deserializer now uses ``yaml.safe_load``
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

``yaml.load`` is able to construct any Python object, which may trigger
arbitrary code execution if you process a YAML document that comes from an
untrusted source. This feature isn't necessary for Django's YAML deserializer,
whose primary use is to load fixtures consisting of simple objects. Even though
fixtures are trusted data, for additional security, the YAML deserializer now
uses ``yaml.safe_load``.

Features deprecated in 1.4
==========================

Old styles of calling ``cache_page`` decorator
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Some legacy ways of calling :func:`~django.views.decorators.cache.cache_page`
have been deprecated, please see the docs for the correct way to use this
decorator.

Support for PostgreSQL versions older than 8.2
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Django 1.3 dropped support for PostgreSQL versions older than 8.0 and the
relevant documents suggested to use a recent version because of performance
reasons but more importantly because end of the upstream support periods for
releases 8.0 and 8.1 was near (November 2010.)

Django 1.4 takes that policy further and sets 8.2 as the minimum PostgreSQL
version it officially supports.

Request exceptions are now always logged
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

When :doc:`logging support </topics/logging/>` was added to Django in 1.3, the
admin error email support was moved into the
:class:`django.utils.log.AdminEmailHandler`, attached to the
``'django.request'`` logger. In order to maintain the established behavior of
error emails, the ``'django.request'`` logger was called only when
:setting:`DEBUG` was `False`.

To increase the flexibility of request-error logging, the ``'django.request'``
logger is now called regardless of the value of :setting:`DEBUG`, and the
default settings file for new projects now includes a separate filter attached
to :class:`django.utils.log.AdminEmailHandler` to prevent admin error emails in
`DEBUG` mode::

   'filters': {
        'require_debug_false': {
            '()': 'django.utils.log.RequireDebugFalse'
        }
    },
    'handlers': {
        'mail_admins': {
            'level': 'ERROR',
            'filters': ['require_debug_false'],
            'class': 'django.utils.log.AdminEmailHandler'
        }
    },

If your project was created prior to this change, your :setting:`LOGGING`
setting will not include this new filter. In order to maintain
backwards-compatibility, Django will detect that your ``'mail_admins'`` handler
configuration includes no ``'filters'`` section, and will automatically add
this filter for you and issue a pending-deprecation warning. This will become a
deprecation warning in Django 1.5, and in Django 1.6 the
backwards-compatibility shim will be removed entirely.

The existence of any ``'filters'`` key under the ``'mail_admins'`` handler will
disable this backward-compatibility shim and deprecation warning.

``django.conf.urls.defaults``
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Until Django 1.3 the functions :func:`~django.conf.urls.include`,
:func:`~django.conf.urls.patterns` and :func:`~django.conf.urls.url` plus
:data:`~django.conf.urls.handler404`, :data:`~django.conf.urls.handler500`
were located in a ``django.conf.urls.defaults`` module.

Starting with Django 1.4 they are now available in :mod:`django.conf.urls`.

``django.contrib.databrowse``
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Databrowse has not seen active development for some time, and this does not
show any sign of changing. There had been a suggestion for a GSOC project to
integrate the functionality of databrowse into the admin, but no progress was
made. While Databrowse has been deprecated, an enhancement of
django.contrib.admin providing a similar feature set is still possible.

.. _GSOC Proposal: https://code.djangoproject.com/wiki/SummerOfCode2011#Integratedatabrowseintotheadmin

The code that powers Databrowse is licensed under the same terms as Django
itself, and so is available to be adopted by an individual or group as
a third-party project.

``django.core.management.setup_environ``
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

This function temporarily modified ``sys.path`` in order to make the parent
"project" directory importable under the old flat :djadmin:`startproject`
layout. This function is now deprecated, as its path workarounds are no longer
needed with the new ``manage.py`` and default project layout.

This function was never documented or public API, but was widely recommended
for use in setting up a "Django environment" for a user script. These uses
should be replaced by setting the ``DJANGO_SETTINGS_MODULE`` environment
variable or using :func:`django.conf.settings.configure`.

``django.core.management.execute_manager``
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

This function was previously used by ``manage.py`` to execute a management
command. It is identical to
``django.core.management.execute_from_command_line``, except that it first
calls ``setup_environ``, which is now deprecated. ``execute_manager`` is also
deprecated; ``execute_from_command_line`` can be used instead. (Neither of
these functions is documented public API, but a deprecation path is needed due
to use in existing ``manage.py`` files.)

``is_safe`` and ``needs_autoescape`` attributes of template filters
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Two flags, ``is_safe`` and ``needs_autoescape``, define how each template filter
interacts with Django's auto-escaping behavior. They used to be attributes of
the filter function::

    @register.filter
    def noop(value):
        return value
    noop.is_safe = True

However, this technique caused some problems in combination with decorators,
especially :func:`@stringfilter <django.template.defaultfilters.stringfilter>`.
Now, the flags are keyword arguments of :meth:`@register.filter
<django.template.Library.filter>`::

    @register.filter(is_safe=True)
    def noop(value):
        return value

See :ref:`filters and auto-escaping <filters-auto-escaping>` for more information.

Session cookies now have the ``httponly`` flag by default
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Session cookies now include the ``httponly`` attribute by default to
help reduce the impact of potential XSS attacks. For strict backwards
compatibility, use ``SESSION_COOKIE_HTTPONLY = False`` in settings.

Wildcard expansion of application names in `INSTALLED_APPS`
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Until Django 1.3, :setting:`INSTALLED_APPS` accepted wildcards in application
names, like ``django.contrib.*``. The expansion was performed by a
filesystem-based implementation of ``from <package> import *``. Unfortunately,
`this can't be done reliably`_.

This behavior was never documented. Since it is un-pythonic and not obviously
useful, it was removed in Django 1.4. If you relied on it, you must edit your
settings file to list all your applications explicitly.

.. _this can't be done reliably: http://docs.python.org/tutorial/modules.html#importing-from-a-package

``HttpRequest.raw_post_data`` renamed to ``HttpRequest.body``
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

This attribute was confusingly named ``HttpRequest.raw_post_data``, but it
actually provided the body of the HTTP request. It's been renamed to
``HttpRequest.body``, and ``HttpRequest.raw_post_data`` has been deprecated.

The Django 1.4 roadmap
======================

Before the final Django 1.4 release, several other preview/development releases
will be made available. The current schedule consists of at least the following:

* Week of **January 30, 2012**: First Django 1.4 beta release; final
  feature freeze for Django 1.4.

* Week of **February 27, 2012**: First Django 1.4 release
  candidate; string freeze for translations.

* Week of **March 5, 2011**: Django 1.4 final release.

If necessary, additional alpha, beta or release-candidate packages
will be issued prior to the final 1.4 release. Django 1.4 will be
released approximately one week after the final release candidate.

What you can do to help
=======================

In order to provide a high-quality 1.4 release, we need your help. Although this
alpha release is, again, *not* intended for production use, you can help the
Django team by trying out the alpha codebase in a safe test environment and
reporting any bugs or issues you encounter. The Django ticket tracker is the
central place to search for open issues:

* http://code.djangoproject.com/timeline

Please open new tickets if no existing ticket corresponds to a problem you're
running into.

Additionally, discussion of Django development, including progress toward the
1.3 release, takes place daily on the django-developers mailing list:

* http://groups.google.com/group/django-developers

... and in the ``#django-dev`` IRC channel on ``irc.freenode.net``. If you're
interested in helping out with Django's development, feel free to join the
discussions there.

Django's online documentation also includes pointers on how to contribute to
Django:

* :doc:`How to contribute to Django </internals/contributing/index>`

Contributions on any level -- developing code, writing documentation or simply
triaging tickets and helping to test proposed bugfixes -- are always welcome and
appreciated.

Several development sprints will also be taking place before the 1.4
release; these will typically be announced in advance on the
django-developers mailing list, and anyone who wants to help is
welcome to join in.