Task retry and error handling in Django - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to retry a task after failure using Celery's retry method.

Django

from celery import shared_task

@shared_task(bind=True)
def fetch_data(self):
    try:
        # code that might fail
        pass
    except Exception as e:
        raise self.[1](exc=e, countdown=5)

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

Aabort

Bfail

Cretry

Dstop

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'fail' or 'abort' instead of 'retry' causes the task to stop immediately.

Not using 'self.' before the method causes an error.

The retry method is used inside a Celery task to retry the task after an exception.

2fill in blank

medium

Complete the code to catch a specific exception and retry the task.

Django

from celery import shared_task

@shared_task(bind=True)
def process_file(self, filename):
    try:
        # process the file
        pass
    except [1] as e:
        raise self.retry(exc=e, countdown=10)

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

ATypeError

BValueError

CKeyError

DFileNotFoundError

Attempts:

3 left

💡 Hint

Common Mistakes

Catching the wrong exception causes the retry not to trigger.

Using a generic exception hides specific errors.

We catch FileNotFoundError to retry when the file is missing.

3fill in blank

hard

Fix the error in the task to properly handle retries with max retries limit.

Django

from celery import shared_task

@shared_task(bind=True, max_retries=3)
def send_email(self, user_id):
    try:
        # send email code
        pass
    except Exception as e:
        raise self.retry(exc=e, countdown=[1])

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

A5

B10

C60

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using zero causes immediate retry and possible overload.

Using too large values delays retries unnecessarily.

The countdown sets the delay before retry. 5 seconds is a reasonable retry delay.

4fill in blank

hard

Fill both blanks to catch a timeout error and retry after 15 seconds.

Django

from celery import shared_task
import requests

@shared_task(bind=True)
def fetch_url(self, url):
    try:
        response = requests.get(url, timeout=5)
    except [1] as e:
        raise self.retry(exc=e, countdown=[2])

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

Arequests.exceptions.Timeout

Brequests.exceptions.ConnectionError

C10

D15

Attempts:

3 left

💡 Hint

Common Mistakes

Catching the wrong exception causes no retry.

Using wrong countdown delays retries incorrectly.

We catch requests.exceptions.Timeout and retry after 15 seconds.

5fill in blank

hard

Fill all three blanks to create a task that retries on ValueError with max 4 retries and 20 seconds delay.

Django

from celery import shared_task

@shared_task(bind=True, max_retries=[1])
def calculate(self, data):
    try:
        # calculation code
        pass
    except [2] as e:
        raise self.retry(exc=e, countdown=[3])

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

A4

BValueError

C20

D3

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong exception type prevents retry.

Setting max_retries too low or countdown too short.

The task retries up to 4 times on ValueError with 20 seconds delay between retries.

Practice

1. What is the main purpose of using task retry in Django background tasks?

easy

A. To automatically try the task again if it fails temporarily

B. To stop the task immediately when an error occurs

C. To speed up the task execution by running it multiple times

D. To log the task output without retrying

Solution

1. Step 1: Understand task retry concept

   Task retry is used to handle temporary failures by trying the task again later.

2. Step 2: Identify the purpose in Django tasks

   It helps tasks recover from temporary errors without manual intervention.

3. Final Answer:

   To automatically try the task again if it fails temporarily -> Option A

4. Quick Check:

   Task retry = automatic retry on failure [OK]

Hint: Retry means try again automatically after failure [OK]

Common Mistakes:

• Thinking retry stops the task immediately
• Confusing retry with speeding up tasks
• Assuming retry only logs errors

2. Which of the following is the correct way to enable retry inside a Django task using Celery?

easy

A. @app.task(bind=True)\ndef my_task(self): self.retry(countdown=10)

B. def my_task(self): retry()

C. @app.task()\ndef my_task(): retry(countdown=10)

D. def my_task(): self.retry(countdown=10)

Solution

1. Step 1: Recognize the need for bind=True

   To use self.retry(), the task must be bound with bind=True.

2. Step 2: Check correct syntax for retry call

   The retry method is called on self inside the bound task function.

3. Final Answer:

   @app.task(bind=True)\ndef my_task(self): self.retry(countdown=10) -> Option A

4. Quick Check:

   bind=True + self.retry() = correct retry syntax [OK]

Hint: Use bind=True to access self.retry inside task [OK]

Common Mistakes:

• Not using bind=True and calling self.retry
• Calling retry without self or decorator
• Missing parentheses or wrong function signature

3. Given this task code snippet, what will happen if the task raises an exception on the first run?

@app.task(bind=True, max_retries=3)
def fetch_data(self):
    try:
        # code that may fail
        raise ValueError('Temporary error')
    except Exception as exc:
        raise self.retry(exc=exc, countdown=5)

medium

A. The task retries once and then stops

B. The task fails immediately without retrying

C. The task retries infinitely every 5 seconds

D. The task retries up to 3 times with 5 seconds delay between tries

Solution

1. Step 1: Analyze max_retries parameter

   max_retries=3 means the task will retry up to 3 times after failure.

2. Step 2: Understand retry call with countdown

   self.retry is called with countdown=5, so retries wait 5 seconds before next try.

3. Final Answer:

   The task retries up to 3 times with 5 seconds delay between tries -> Option D

4. Quick Check:

   max_retries=3 + countdown=5 = 3 retries with 5s delay [OK]

Hint: max_retries limits retries; countdown sets delay [OK]

Common Mistakes:

• Assuming infinite retries without max_retries
• Thinking retry happens immediately without delay
• Confusing max_retries with number of total runs

4. Identify the error in this Django Celery task code that tries to retry on failure:

@app.task(bind=True)
def process_data():
    try:
        # risky operation
        pass
    except Exception as e:
        self.retry(exc=e, countdown=10)

medium

A. retry method called outside except block

B. No max_retries set, so retry won't work

C. Missing self parameter in task function definition

D. Incorrect exception handling syntax

Solution

1. Step 1: Check function signature for bound task

   With bind=True, the task function must accept self as first parameter.

2. Step 2: Verify usage of self.retry

   self.retry is called, but self is undefined because function lacks self parameter.

3. Final Answer:

   Missing self parameter in task function definition -> Option C

4. Quick Check:

   bind=True requires self parameter [OK]

Hint: bind=True means add self parameter to task function [OK]

Common Mistakes:

• Forgetting self parameter with bind=True
• Calling retry outside except block
• Assuming max_retries is mandatory for retry

5. You want a Django Celery task to retry only on network errors but fail immediately on other exceptions. Which approach correctly implements this behavior?

hard

A. Set max_retries=0 and catch all exceptions to call self.retry

B. Use try-except to catch network errors and call self.retry; re-raise other exceptions

C. Call self.retry unconditionally in except block for all exceptions

D. Use a decorator to retry on all exceptions automatically

Solution

1. Step 1: Differentiate exception types in except block

   Catch only network-related exceptions to retry, others should raise immediately.

2. Step 2: Use self.retry only for network errors

   Call self.retry inside except for network errors; re-raise other exceptions to fail fast.

3. Final Answer:

   Use try-except to catch network errors and call self.retry; re-raise other exceptions -> Option B

4. Quick Check:

   Retry selectively by exception type using try-except [OK]

Hint: Retry only inside except for specific exceptions [OK]

Common Mistakes:

• Retrying on all exceptions without filtering
• Setting max_retries=0 disables retries
• Using decorators without exception control