signals.txt

.. _ref-signals:

=========================
Built-in signal reference
=========================

A list of all the signals that Django sends.

.. seealso::

    The :ref:`comment framework <ref-contrib-comments-index>` sends a :ref:`set
    of comment-related signals <ref-contrib-comments-signals>`.

Model signals
=============

.. module:: django.db.models.signals
   :synopsis: Signals sent by the model system.

The :mod:`django.db.models.signals` module defines a set of signals sent by the
module system.

.. warning::

    Many of these signals are sent by various model methods like
    :meth:`~django.db.models.Model.__init__` or
    :meth:`~django.db.models.Model.save` that you can overwrite in your own
    code.

    If you override these methods on your model, you must call the parent class'
    methods for this signals to be sent.

pre_init
--------

.. attribute:: django.db.models.signals.pre_init
   :module:

.. ^^^^^^^ this :module: hack keeps Sphinx from prepending the module.

Whenever you instantiate a Django model,, this signal is sent at the beginning
of the model's :meth:`~django.db.models.Model.__init__` method.

Arguments sent with this signal:

    ``sender``
        The model class that just had an instance created.

    ``args``
        A list of positional arguments passed to
        :meth:`~django.db.models.Model.__init__`:

    ``kwargs``
        A dictionary of keyword arguments passed to
        :meth:`~django.db.models.Model.__init__`:.

For example, the :ref:`tutorial <intro-tutorial01>` has this line:

.. code-block:: python

    p = Poll(question="What's up?", pub_date=datetime.now())

The arguments sent to a :data:`pre_init` handler would be:

    ==========  ===============================================================
    Argument    Value
    ==========  ===============================================================
    ``sender``  ``Poll`` (the class itself)

    ``args``    ``[]`` (an empty list because there were no positional
                arguments passed to ``__init__``.)

    ``kwargs``  ``{'question': "What's up?", 'pub_date': datetime.now()}``
    ==========  ===============================================================

post_init
---------

.. data:: django.db.models.signals.post_init
   :module:

Like pre_init, but this one is sent when the :meth:`~django.db.models.Model.__init__`: method finishes.

Arguments sent with this signal:

    ``sender``
        As above: rhe model class that just had an instance created.

    ``instance``
        The actual instance of the model that's just been created.

pre_save
--------

.. data:: django.db.models.signals.pre_save
   :module:
   
This is sent at the beginning of a model's :meth:`~django.db.models.Model.save`
method.

Arguments sent with this signal:

    ``sender``
        The model class.

    ``instance``
        The actual instance being saved.

post_save
---------

.. data:: django.db.models.signals.post_save
   :module: 
   
Like :data:`pre_save`, but sent at the end of the
:meth:`~django.db.models.Model.save` method.

Arguments sent with this signal:

    ``sender``
        The model class.

    ``instance``
        The actual instance being saved.

    ``created``
        A boolean; ``True`` if a new record was create.

pre_delete
----------

.. data:: django.db.models.signals.pre_delete
   :module:
   
Sent at the beginning of a model's :meth:`~django.db.models.Model.delete`
method.

Arguments sent with this signal:

    ``sender``
        The model class.

    ``instance``
        The actual instance being saved.

post_delete
-----------

.. data:: django.db.models.signals.post_delete
   :module: 
   
Like :data:`pre_delete`, but sent at the end of the
:meth:`~django.db.models.Model.delete` method.

Arguments sent with this signal:

    ``sender``
        The model class.

    ``instance``
        The actual instance being saved.

        Note that the object will no longer be in the database, so be very
        careful what you do with this instance

class_prepared
--------------

.. data:: django.db.models.signals.class_prepared
   :module:
   
Sent whenever a model class has been "prepared" -- that is, once model has
been defined and registered with Django's model system. Django uses this
signal internally; it's not generally used in third-party applications.

Arguments that are sent with this signal:

``sender``
    The model class which was just prepared.

Management signals
==================

Signals sent by :ref:`django-admin <ref-django-admin>`.

post_syncdb
-----------

.. data:: django.db.models.signals.post_syncdb
   :module:

Sent by :djadmin:`syncdb` after it installs an application.

Any handlers that listen to this signal need to be written in a particular
place: a ``management`` module in one of your :setting:`INSTALLED_APPS`. If
handlers are registered anywhere else they may not be loaded by
:djadmin:`syncdb`.

Arguments sent with this signal:

    ``sender``
        The ``models`` module that was just installed. That is, if
        :djadmin:`syncdb` just installed an app called ``"foo.bar.myapp"``,
        ``sender`` will be the ``foo.bar.myapp.models`` module.

    ``app``
        Same as ``sender``.

    ``created_models``
        A list of the model classes from any app which :djadmin:`syncdb` has
        created so far.

    ``verbosity``
        Indicates how much information manage.py is printing on screen. See
        the :djadminopt:`--verbosity`` flag for details.

        Functions which listen for :data:`post_syncdb` should adjust what they
        output to the screen based on the value of this argument.

    ``interactive``
        If ``interactive`` is ``True``, it's safe to prompt the user to input
        things on the command line. If ``interactive`` is ``False``, functions
        which listen for this signal should not try to prompt for anything.

        For example, the :mod:`django.contrib.auth` app only prompts to create a
        superuser when ``interactive`` is ``True``.

Request/response signals
========================

.. module:: django.core.signals
   :synopsis: Core signals sent by the request/response system.

Signals sent by the core framework when processing a request.

request_started
---------------

.. data:: django.core.signals.request_started
   :module: 
   
Sent when Django begins processing an HTTP request.

Arguments sent with this signal:

    ``sender``
        The handler class -- i.e.
        :class:`django.core.handlers.modpython.ModPythonHandler` or
        :class:`django.core.handlers.wsgi.WsgiHandler` -- that handled
        the request.

request_finished
----------------

.. data:: django.core.signals.request_finished
   :module:
   
Sent when Django finishes processing an HTTP request.

Arguments sent with this signal:

    ``sender``
        The handler class, as above.

got_request_exception
---------------------

.. data:: django.core.signals.got_request_exception
   :module:
   
This signal is sent whenever Django encounters an exception while processing an incoming HTTP request.

Arguments sent with this signal:

    ``sender``
        The handler class, as above.

    ``request``
        The :class:`~django.http.HttpRequest` object.

Test signals
============

.. module:: django.test.signals
   :synopsis: Signals sent during testing.

Signals only sent when :ref:`running tests <topics-testing>`.

template_rendered
-----------------

.. data:: django.test.signals.template_rendered
   :module:
   
Sent when the test system renders a template. This signal is not emitted during
normal operation of a Django server -- it is only available during testing.

Arguments sent with this signal:

    sender
        The :class:`~django.template.Template` object which was rendered.

    template
        Same as sender

    context
        The :class:`~django.template.Context` with which the template was
        rendered.