Celery integration overview in Flask - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import Celery in a Flask app.

Flask

from flask import Flask
from [1] import Celery

app = Flask(__name__)
celery = Celery(app.name, broker='redis://localhost:6379/0')

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

Acelery

Bflask_celery

Cflaskext

Dflask_celery_worker

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to import Celery from 'flask_celery' or other non-existent packages.

Forgetting to import Celery at all.

You import Celery directly from the celery package to use it with Flask.

2fill in blank

medium

Complete the code to define a Celery task in Flask.

Flask

@celery.task
def [1](x, y):
    return x + y

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

Acalculate

Badd_numbers

Csum

Dtask

Attempts:

3 left

💡 Hint

Common Mistakes

Using Python built-in names like 'sum' as function names.

Not decorating the function with @celery.task.

The function name can be anything, but add_numbers clearly describes the task.

3fill in blank

hard

Fix the error in the Celery configuration for Flask.

Flask

app.config.update(
    CELERY_BROKER_URL='[1]',
    CELERY_RESULT_BACKEND='redis://localhost:6379/0'
)

celery.conf.update(app.config)

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

Ahttp://localhost:6379

Bredis://127.0.0.1:6379/0

Camqp://guest@localhost//

Dredis://localhost:6379/0

Attempts:

3 left

💡 Hint

Common Mistakes

Using Redis URL as broker when RabbitMQ is intended.

Using HTTP URLs which are invalid for brokers.

The broker URL for Celery using RabbitMQ is amqp://guest@localhost//. Redis URLs start with redis://.

4fill in blank

hard

Fill both blanks to create a Celery instance with Flask app context.

Flask

def make_celery(app):
    celery = Celery(app.import_name, broker=app.config['[1]'])
    celery.conf.update(app.config)

    class ContextTask(celery.Task):
        def __call__(self, *args, **kwargs):
            with app.app_context():
                return self.run(*args, **kwargs)

    celery.Task = [2]
    return celery

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

ACELERY_BROKER_URL

BCELERY_RESULT_BACKEND

CContextTask

DTask

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong config key for the broker URL.

Assigning the wrong class to celery.Task.

The broker URL is stored in CELERY_BROKER_URL. The custom task class ContextTask ensures Flask app context during task execution.

5fill in blank

hard

Fill all three blanks to call a Celery task asynchronously and get the result.

Flask

result = [1].delay(10, 20)
output = result.[2]()
print('Task result:', [3])

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

Aadd_numbers

Bget

Coutput

Dresult

Attempts:

3 left

💡 Hint

Common Mistakes

Calling the task function directly instead of using delay.

Using wrong variable names for the result or output.

You call the task function add_numbers with delay to run asynchronously. Then use get() on the result to wait and fetch the output. Finally, print the output variable.

Practice

1. What is the main purpose of integrating Celery with a Flask application?

easy

A. To run tasks in the background without blocking the main app

B. To create HTML templates for the Flask app

C. To handle user authentication and sessions

D. To serve static files like images and CSS

Solution

1. Step 1: Understand Celery's role

   Celery is designed to run tasks asynchronously, meaning it handles work in the background.

2. Step 2: Connect to Flask app purpose

   Flask apps use Celery to keep the app responsive by offloading long tasks.

3. Final Answer:

   To run tasks in the background without blocking the main app -> Option A

4. Quick Check:

   Celery = background tasks [OK]

Hint: Celery = background task runner in Flask apps [OK]

Common Mistakes:

• Thinking Celery manages templates
• Confusing Celery with user login features
• Assuming Celery serves static files

2. Which of the following is the correct way to define a Celery task in a Flask app?

easy

A. @celery_app.task\ndef add(x, y): return x + y

B. celery_app.run_task(add)

C. @app.route('/task')\ndef task(): pass

D. def task(): pass

Solution

1. Step 1: Identify Celery task decorator

   Celery tasks are defined using the @celery_app.task decorator.

2. Step 2: Check syntax correctness

   @celery_app.task\ndef add(x, y): return x + y correctly decorates a function to become a Celery task.

3. Final Answer:

   @celery_app.task\ndef add(x, y): return x + y -> Option A

4. Quick Check:

   Celery task = @celery_app.task decorator [OK]

Hint: Use @celery_app.task to define tasks [OK]

Common Mistakes:

• Forgetting the @celery_app.task decorator
• Using Flask route decorators for tasks
• Calling celery_app.run_task which is invalid

3. Given this code snippet in a Flask app with Celery:

@celery_app.task
def multiply(x, y):
    return x * y

result = multiply.delay(3, 4)
print(result.get())

What will be printed?

medium

A. A task object reference

B. null

C. 12

D. An error because delay() is not valid

Solution

1. Step 1: Understand delay() usage

   Calling multiply.delay(3, 4) sends the task to Celery to run asynchronously.

2. Step 2: Using get() to wait for result

   result.get() waits for the task to finish and returns the output, which is 3 * 4 = 12.

3. Final Answer:

   12 -> Option C

4. Quick Check:

   delay() runs task, get() returns result [OK]

Hint: delay() runs task, get() fetches result [OK]

Common Mistakes:

• Thinking delay() returns the result immediately
• Confusing task object with result value
• Assuming delay() is invalid in Celery

4. You wrote this Celery task in your Flask app:

@celery_app.task
def add(x, y):
return x + y

But when you call add.delay(2, 3), it raises an IndentationError. What is the problem?

medium

A. delay() cannot be called on tasks

B. The function body is not indented properly

C. You forgot to import Celery

D. The decorator syntax is incorrect

Solution

1. Step 1: Check function indentation

   Python requires the function body to be indented under the def line.

2. Step 2: Identify error cause

   Here, return x + y is not indented, causing IndentationError.

3. Final Answer:

   The function body is not indented properly -> Option B

4. Quick Check:

   Python needs indented function bodies [OK]

Hint: Indent function body under def line [OK]

Common Mistakes:

• Ignoring Python indentation rules
• Assuming delay() is invalid
• Thinking decorator syntax is wrong

5. You want to integrate Celery with Flask using Redis as the broker. Which steps correctly describe the setup process?

hard

A. Install Celery only, define tasks without decorator, call tasks directly, no broker needed

B. Install Flask-Login, configure Celery with SQLite, define tasks with @app.route, call tasks with run()

C. Install Redis, configure Flask routes for tasks, use delay() without decorator, run Redis server

D. Install Redis, configure Celery with Redis URL, define tasks with @celery_app.task, call tasks with delay()

Solution

1. Step 1: Setup Redis broker

   Redis must be installed and running as the message broker for Celery.

2. Step 2: Configure Celery and define tasks

   Celery is configured with Redis URL, tasks use @celery_app.task, and are called with delay().

3. Final Answer:

   Install Redis, configure Celery with Redis URL, define tasks with @celery_app.task, call tasks with delay() -> Option D

4. Quick Check:

   Redis + @celery_app.task + delay() = correct setup [OK]

Hint: Use Redis broker, @celery_app.task, and delay() calls [OK]

Common Mistakes:

• Using wrong broker like SQLite
• Defining tasks without decorator
• Calling tasks with run() or no broker