Signals

A list of all the signals that Django sends. All built-in signals are sent using the send() method.

Model signals

The django.db.models.signals module defines a set of signals sent by the model system.

pre_init

django.db.models.signals.pre_init

Whenever you instantiate a Django model, this signal is sent at the beginning of the model’s __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 __init__().

kwargs

A dictionary of keyword arguments passed to __init__().

For example, the tutorial has this line:

q = Question(question_text="What's new?", pub_date=timezone.now())

The arguments sent to a pre_init handler would be:

Argument	Value
sender	Question (the class itself)
args	[] (an empty list because there were no positional arguments passed to __init__())
kwargs	{'question_text': "What's new?", 'pub_date': datetime.datetime(2012, 2, 26, 13, 0, 0, 775217, tzinfo=<UTC>)}

post_init

django.db.models.signals.post_init

Like pre_init, but this one is sent when the __init__() method finishes.

Arguments sent with this signal:

sender

As above: the model class that just had an instance created.

instance

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

Note

instance._state isn’t set before sending the post_init signal, so _state attributes always have their default values. For example, _state.db is None.

pre_save

django.db.models.signals.pre_save

This is sent at the beginning of a model’s save() method.

Arguments sent with this signal:

sender

The model class.

instance

The actual instance being saved.

raw

A boolean; True if the model is saved exactly as presented (i.e. when loading a fixture). One should not query/modify other records in the database as the database might not be in a consistent state yet.

using

The database alias being used.

update_fields

The set of fields to update as passed to Model.save(), or None if update_fields wasn’t passed to save().

post_save

django.db.models.signals.post_save

Like pre_save, but sent at the end of the 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 created.

raw

A boolean; True if the model is saved exactly as presented (i.e. when loading a fixture). One should not query/modify other records in the database as the database might not be in a consistent state yet.

using

The database alias being used.

update_fields

The set of fields to update as passed to Model.save(), or None if update_fields wasn’t passed to save().

pre_delete

django.db.models.signals.pre_delete

Sent at the beginning of a model’s delete() method and a queryset’s delete() method.

Arguments sent with this signal:

sender

The model class.

instance

The actual instance being deleted.

using

The database alias being used.

post_delete

django.db.models.signals.post_delete

Like pre_delete, but sent at the end of a model’s delete() method and a queryset’s delete() method.

Arguments sent with this signal:

sender

The model class.

instance

The actual instance being deleted.

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

using

The database alias being used.

m2m_changed

django.db.models.signals.m2m_changed

Sent when a ManyToManyField is changed on a model instance. Strictly speaking, this is not a model signal since it is sent by the ManyToManyField, but since it complements the pre_save/post_save and pre_delete/post_delete when it comes to tracking changes to models, it is included here.

Arguments sent with this signal:

sender

The intermediate model class describing the ManyToManyField. This class is automatically created when a many-to-many field is defined; you can access it using the through attribute on the many-to-many field.

instance

The instance whose many-to-many relation is updated. This can be an instance of the sender, or of the class the ManyToManyField is related to.

action

A string indicating the type of update that is done on the relation. This can be one of the following:

"pre_add"

Sent before one or more objects are added to the relation.

"post_add"

Sent after one or more objects are added to the relation.

"pre_remove"

Sent before one or more objects are removed from the relation.

"post_remove"

Sent after one or more objects are removed from the relation.

"pre_clear"

Sent before the relation is cleared.

"post_clear"

Sent after the relation is cleared.

reverse

Indicates which side of the relation is updated (i.e., if it is the forward or reverse relation that is being modified).

model

The class of the objects that are added to, removed from or cleared from the relation.

pk_set

For the pre_add and post_add actions, this is a set of primary key values that will be, or have been, added to the relation. This may be a subset of the values submitted to be added, since inserts must filter existing values in order to avoid a database IntegrityError.

For the pre_remove and post_remove actions, this is a set of primary key values that was submitted to be removed from the relation. This is not dependent on whether the values actually will be, or have been, removed. In particular, non-existent values may be submitted, and will appear in pk_set, even though they have no effect on the database.

For the pre_clear and post_clear actions, this is None.

using

The database alias being used.

For example, if a Pizza can have multiple Topping objects, modeled like this:

class Topping(models.Model):
    # ...
    pass

class Pizza(models.Model):
    # ...
    toppings = models.ManyToManyField(Topping)

If we connected a handler like this:

from django.db.models.signals import m2m_changed

def toppings_changed(sender, **kwargs):
    # Do something
    pass

m2m_changed.connect(toppings_changed, sender=Pizza.toppings.through)

and then did something like this:

>>> p = Pizza.objects.create(...)
>>> t = Topping.objects.create(...)
>>> p.toppings.add(t)

the arguments sent to a m2m_changed handler (toppings_changed in the example above) would be:

Argument	Value
sender	Pizza.toppings.through (the intermediate m2m class)
instance	p (the Pizza instance being modified)
action	"pre_add" (followed by a separate signal with "post_add")
reverse	False (Pizza contains the ManyToManyField, so this call modifies the forward relation)
model	Topping (the class of the objects added to the Pizza)
pk_set	{t.id} (since only Topping t was added to the relation)
using	"default" (since the default router sends writes here)

And if we would then do something like this:

>>> t.pizza_set.remove(p)

the arguments sent to a m2m_changed handler would be:

Argument	Value
sender	Pizza.toppings.through (the intermediate m2m class)
instance	t (the Topping instance being modified)
action	"pre_remove" (followed by a separate signal with "post_remove")
reverse	True (Pizza contains the ManyToManyField, so this call modifies the reverse relation)
model	Pizza (the class of the objects removed from the Topping)
pk_set	{p.id} (since only Pizza p was removed from the relation)
using	"default" (since the default router sends writes here)

class_prepared

django.db.models.signals.class_prepared

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.

Since this signal is sent during the app registry population process, and AppConfig.ready() runs after the app registry is fully populated, receivers cannot be connected in that method. One possibility is to connect them AppConfig.__init__() instead, taking care not to import models or trigger calls to the app registry.

Arguments that are sent with this signal:

sender

The model class which was just prepared.

Management signals

Signals sent by django-admin.

pre_migrate

django.db.models.signals.pre_migrate

Sent by the migrate command before it starts to install an application. It’s not emitted for applications that lack a models module.

Arguments sent with this signal:

sender

An AppConfig instance for the application about to be migrated/synced.

app_config

Same as sender.

verbosity

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

Functions which listen for pre_migrate 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 django.contrib.auth app only prompts to create a superuser when interactive is True.

using

The alias of database on which a command will operate.

plan

The migration plan that is going to be used for the migration run. While the plan is not public API, this allows for the rare cases when it is necessary to know the plan. A plan is a list of two-tuples with the first item being the instance of a migration class and the second item showing if the migration was rolled back (True) or applied (False).

apps

An instance of Apps containing the state of the project before the migration run. It should be used instead of the global apps registry to retrieve the models you want to perform operations on.

post_migrate

django.db.models.signals.post_migrate

Sent at the end of the migrate (even if no migrations are run) and flush commands. It’s not emitted for applications that lack a models module.

Handlers of this signal must not perform database schema alterations as doing so may cause the flush command to fail if it runs during the migrate command.

Arguments sent with this signal:

sender

An AppConfig instance for the application that was just installed.

app_config

Same as sender.

verbosity

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

Functions which listen for post_migrate 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 django.contrib.auth app only prompts to create a superuser when interactive is True.

using

The database alias used for synchronization. Defaults to the default database.

plan

The migration plan that was used for the migration run. While the plan is not public API, this allows for the rare cases when it is necessary to know the plan. A plan is a list of two-tuples with the first item being the instance of a migration class and the second item showing if the migration was rolled back (True) or applied (False).

apps

An instance of Apps containing the state of the project after the migration run. It should be used instead of the global apps registry to retrieve the models you want to perform operations on.

For example, you could register a callback in an AppConfig like this:

from django.apps import AppConfig
from django.db.models.signals import post_migrate

def my_callback(sender, **kwargs):
    # Your specific logic here
    pass

class MyAppConfig(AppConfig):
    ...

    def ready(self):
        post_migrate.connect(my_callback, sender=self)

Request/response signals

Signals sent by the core framework when processing a request.

request_started

django.core.signals.request_started

Sent when Django begins processing an HTTP request.

Arguments sent with this signal:

sender

The handler class – e.g. django.core.handlers.wsgi.WsgiHandler – that handled the request.

environ

The environ dictionary provided to the request.

request_finished

django.core.signals.request_finished

Sent when Django finishes delivering an HTTP response to the client.

Arguments sent with this signal:

sender

The handler class, as above.

got_request_exception

django.core.signals.got_request_exception

This signal is sent whenever Django encounters an exception while processing an incoming HTTP request.

Arguments sent with this signal:

sender

Unused (always None).

request

The HttpRequest object.

Test signals

Signals only sent when running tests.

setting_changed

django.test.signals.setting_changed

This signal is sent when the value of a setting is changed through the django.test.TestCase.settings() context manager or the django.test.override_settings() decorator/context manager.

It’s actually sent twice: when the new value is applied (“setup”) and when the original value is restored (“teardown”). Use the enter argument to distinguish between the two.

You can also import this signal from django.core.signals to avoid importing from django.test in non-test situations.

Arguments sent with this signal:

sender

The settings handler.

setting

The name of the setting.

value

The value of the setting after the change. For settings that initially don’t exist, in the “teardown” phase, value is None.

enter

A boolean; True if the setting is applied, False if restored.

template_rendered

django.test.signals.template_rendered

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 Template object which was rendered.

template

Same as sender

context

The Context with which the template was rendered.

Database Wrappers

Signals sent by the database wrapper when a database connection is initiated.

connection_created

django.db.backends.signals.connection_created

Sent when the database wrapper makes the initial connection to the database. This is particularly useful if you’d like to send any post connection commands to the SQL backend.

Arguments sent with this signal:

sender

The database wrapper class – i.e. django.db.backends.postgresql.DatabaseWrapper or django.db.backends.mysql.DatabaseWrapper, etc.

connection

The database connection that was opened. This can be used in a multiple-database configuration to differentiate connection signals from different databases.