When signals are appropriate vs not in Django - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to connect a signal to a receiver function in Django.

Django

from django.db.models.signals import post_save
from django.dispatch import receiver

@receiver([1], sender=MyModel)
def my_handler(sender, instance, **kwargs):
    print('Signal received')

Drag options to blanks, or click blank then click option'

Apre_delete

Bpost_save

Cm2m_changed

Drequest_finished

Attempts:

3 left

💡 Hint

Common Mistakes

Using a signal that triggers before deletion instead of after saving.

Confusing model signals with request signals.

The post_save signal is sent after a model's save() method completes. It is appropriate to connect to this signal to perform actions after saving an instance.

2fill in blank

medium

Complete the code to disconnect a signal receiver in Django.

Django

from django.db.models.signals import post_save

post_save.[1](my_handler, sender=MyModel)

Drag options to blanks, or click blank then click option'

Adisconnect

Bsend

Cconnect

Dregister

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'connect' instead of 'disconnect' to remove a receiver.

Trying to use a method that does not exist on the signal.

The disconnect method removes a previously connected receiver from a signal.

3fill in blank

hard

Fix the error in the signal receiver to avoid side effects during testing.

Django

@receiver(post_save, sender=MyModel)
def my_handler(sender, instance, created, **kwargs):
    if [1]:
        send_welcome_email(instance.email)

Drag options to blanks, or click blank then click option'

Acreated

Binstance

Csender

Dkwargs

Attempts:

3 left

💡 Hint

Common Mistakes

Not checking if the instance is newly created, causing repeated actions.

Using the instance object directly as a condition.

Checking the created flag ensures the action runs only when a new instance is created, avoiding repeated side effects on updates.

4fill in blank

hard

Fill both blanks to create a signal receiver that avoids recursive saves.

Django

@receiver(post_save, sender=MyModel)
def update_related(sender, instance, [1], **[2]):
    if created:
        instance.related_model.update_status()

Drag options to blanks, or click blank then click option'

Acreated

Bkwargs

Cargs

Dinstance

Attempts:

3 left

💡 Hint

Common Mistakes

Missing the 'created' parameter causing unintended repeated actions.

Not including '**kwargs' leading to errors when extra arguments are passed.

The receiver function should accept created to check if the instance is new, and kwargs to catch extra arguments. This helps avoid recursive saves by acting only on creation.

5fill in blank

hard

Fill all three blanks to write a signal receiver that updates a cache only when a model instance is deleted.

Django

@receiver([1], sender=MyModel)
def clear_cache(sender, instance, [2], **[3]):
    cache.delete(f'user_cache_{instance.pk}')

Drag options to blanks, or click blank then click option'

Apre_delete

Busing

Ckwargs

Dpost_save

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'post_save' signal instead of 'pre_delete' for deletion actions.

Omitting required parameters causing runtime errors.

The pre_delete signal triggers before an instance is deleted. The receiver function should accept using and kwargs parameters to match the signal signature and avoid errors.