Task queue concept in Flask - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What happens when a Flask app uses a task queue?

Consider a Flask app that delegates long-running tasks to a task queue like Celery. What is the main benefit of this approach?

A The Flask app will run tasks faster by using multiple CPU cores automatically.

B The Flask app can respond quickly to user requests without waiting for the task to finish.

C The Flask app will store all task results in the browser cache for faster access.

D The Flask app will block user requests until the task queue finishes all tasks.

💡 Hint

Think about how task queues help with long tasks and user experience.

Using a task queue lets the Flask app hand off long tasks to a background worker. This way, the app can quickly reply to users without waiting for the task to complete.

📝 Syntax

intermediate

Which code snippet correctly sends a task to a Celery queue in Flask?

Given a Celery instance named celery and a task function add, which code sends the task asynchronously?

Flask

from celery import Celery
celery = Celery('app')

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

A add.delay(4, 6)

B add.run(4, 6)

C add.apply(4, 6)

D add.call(4, 6)

💡 Hint

Look for the method that queues the task for background execution.

The delay method sends the task to the queue asynchronously. Other methods either run synchronously or do not exist.

❓ state_output

advanced

What is the output of this Flask + Celery task status check?

Assume a Celery task was sent with result = add.delay(2, 3). What will result.ready() return immediately after sending?

Flask

result = add.delay(2, 3)
print(result.ready())

A False

B True

C None

D Raises AttributeError

💡 Hint

Think about whether the task finishes instantly or not.

Immediately after sending, the task is usually not done, so ready() returns False.

🔧 Debug

advanced

Why does this Flask + Celery task never complete?

Given this code, the task never finishes. What is the likely cause?

from celery import Celery
celery = Celery('app')

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

result = multiply.delay(5, 7)
print(result.get(timeout=1))

A The task function multiply has a syntax error.

B The get method does not accept a timeout argument.

C The delay method is not valid for Celery tasks.

D No Celery worker process is running to execute the task.

💡 Hint

Check if the background worker is active to process tasks.

Without a running Celery worker, tasks stay queued and never execute, so get() waits until timeout.

🧠 Conceptual

expert

Which statement best describes task queues in Flask apps?

Choose the most accurate description of how task queues improve Flask app design.

A They replace Flask's routing system to manage HTTP requests more efficiently.

B They automatically convert Flask apps into multi-threaded servers without extra configuration.

C They allow Flask apps to handle heavy or slow tasks asynchronously, improving user experience and scalability.

D They store all user session data in a centralized queue for faster retrieval.

💡 Hint

Think about the role of background processing in web apps.

Task queues let Flask apps offload slow tasks to workers, so the app stays responsive and can scale better.