Periodic tasks with Celery Beat in Flask - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import Celery in a Flask app.

Flask

from celery import [1]

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

Acelery_app

Bcelery

CCeleryApp

DCelery

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase 'celery' which is incorrect.

Using names like 'CeleryApp' which do not exist.

The Celery class is imported with a capital C as Celery.

2fill in blank

medium

Complete the code to create a Celery instance with Flask app name.

Flask

celery = Celery([1])

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

Aapp

B'myapp'

C'celery'

D'flaskapp'

Attempts:

3 left

💡 Hint

Common Mistakes

Passing the Flask app object instead of its name as a string.

Using incorrect string names.

The Celery instance is created with the Flask app name as a string, e.g., 'myapp'.

3fill in blank

hard

Fix the error in the Celery configuration dictionary key for broker URL.

Flask

celery.conf.update({ 'broker_[1]': 'redis://localhost:6379/0' })

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

Aurl

Buri

Caddress

Dlink

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'broker_uri' which is incorrect.

Using 'broker_address' or 'broker_link' which are invalid keys.

The correct key for the broker address is broker_url.

4fill in blank

hard

Fill both blanks to schedule a periodic task every 10 seconds using Celery Beat.

Flask

from celery.schedules import [1]
celery.conf.beat_schedule = {
    'task-every-10-seconds': {
        'task': 'tasks.my_task',
        'schedule': [2](10.0),
    },
}

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

Acrontab

Btimedelta

Cschedule

Dinterval

Attempts:

3 left

💡 Hint

Common Mistakes

Using crontab for seconds interval which is for cron-like schedules.

Using timedelta which is not a Celery schedule.

The interval schedule is used for periodic tasks every fixed seconds.

5fill in blank

hard

Fill all three blanks to define a Celery task function that prints 'Hello' every minute.

Flask

@celery.task
async def [1]():
    print([2])

celery.conf.beat_schedule = {
    'hello-every-minute': {
        'task': '[3]',
        'schedule': interval(60.0),
    },
}

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

Ahello_task

B'Hello'

D'hello_task'

Attempts:

3 left

💡 Hint

Common Mistakes

Using mismatched task names between function and schedule.

Forgetting quotes around the string to print.

The task function is named hello_task. The print statement prints the string 'Hello'. The task name in the schedule is the string 'hello_task'.

Practice

1. What is the main purpose of Celery Beat in a Flask application?

easy

A. To schedule tasks to run automatically at specific times

B. To handle HTTP requests asynchronously

C. To manage database migrations

D. To serve static files efficiently

Solution

1. Step 1: Understand Celery Beat's role

   Celery Beat is a scheduler that triggers tasks periodically without manual intervention.

2. Step 2: Compare with other options

   Handling HTTP requests, managing migrations, and serving static files are unrelated to scheduling tasks.

3. Final Answer:

   To schedule tasks to run automatically at specific times -> Option A

4. Quick Check:

   Celery Beat = Task scheduler [OK]

Hint: Celery Beat is all about timing tasks automatically [OK]

Common Mistakes:

• Confusing Celery Beat with request handling
• Thinking it manages database or static files
• Assuming it runs tasks only once

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

easy

A. @app.route('/task')\ndef my_task():\n print('Hello')

B. @celery.task\ndef my_task():\n print('Hello')

C. def my_task():\n print('Hello')

D. @celery.task\nasync def my_task():\n print('Hello')

Solution

1. Step 1: Identify task decorator

   Periodic tasks in Celery are defined with the @celery.task decorator.

2. Step 2: Check syntax correctness

   @celery.task\ndef my_task():\n print('Hello') correctly uses @celery.task and a normal function. @app.route('/task')\ndef my_task():\n print('Hello') uses Flask route decorator, which is unrelated. def my_task():\n print('Hello') lacks any decorator. @celery.task\nasync def my_task():\n print('Hello') uses async which is not standard for Celery tasks.

3. Final Answer:

   @celery.task\ndef my_task():\n print('Hello') -> Option B

4. Quick Check:

   Use @celery.task to define Celery tasks [OK]

Hint: Use @celery.task decorator for Celery tasks [OK]

Common Mistakes:

• Using Flask route decorator instead of @celery.task
• Defining tasks without any decorator
• Using async def which Celery does not support by default

3. Given this Celery Beat schedule snippet, what will happen?

beat_schedule = {
    'print-every-10-seconds': {
        'task': 'app.print_message',
        'schedule': 10,
    },
}

medium

A. The task runs once after 10 seconds

B. The task runs every 10 minutes

C. The task 'print_message' runs every 10 seconds

D. This code causes a syntax error

Solution

1. Step 1: Understand the schedule value

   The 'schedule' key with value 10 means the task runs every 10 seconds.

2. Step 2: Confirm task repetition

   Celery Beat schedules tasks repeatedly at the interval given, so it runs every 10 seconds, not once or every 10 minutes.

3. Final Answer:

   The task 'print_message' runs every 10 seconds -> Option C

4. Quick Check:

   Schedule=10 means every 10 seconds [OK]

Hint: Schedule number means seconds interval by default [OK]

Common Mistakes:

• Thinking schedule is minutes instead of seconds
• Assuming task runs only once
• Confusing syntax with crontab format

4. Identify the error in this Celery Beat configuration:

beat_schedule = {
    'task1': {
        'task': 'app.task1',
        'schedule': crontab(minute='*/5')
    },
    'task2': {
        'task': 'app.task2',
        'schedule': '10',
    }
}

medium

A. The dictionary keys 'task1' and 'task2' must be integers

B. 'task' names must be functions, not strings

C. Missing import for crontab causes runtime error

D. 'schedule' for 'task2' should be an integer or crontab, not a string

Solution

1. Step 1: Check 'schedule' types

   For 'task1', schedule uses crontab correctly. For 'task2', schedule is a string '10', which should be an integer 10 or a crontab object.

2. Step 2: Validate other parts

   Task names as strings are correct references. Import errors are not shown here. Dictionary keys can be strings.

3. Final Answer:

   'schedule' for 'task2' should be an integer or crontab, not a string -> Option D

4. Quick Check:

   Schedule must be int or crontab, not string [OK]

Hint: Schedule values must be int or crontab, not quoted strings [OK]

Common Mistakes:

• Using string instead of int for schedule interval
• Confusing task names with function objects
• Assuming dictionary keys must be integers

5. You want to run a Flask Celery task every Monday at 8:30 AM using Celery Beat. Which beat_schedule entry is correct?

hard

A. {'task': 'app.weekly_task', 'schedule': crontab(hour=8, minute=30, day_of_week='mon')}

B. {'task': 'app.weekly_task', 'schedule': crontab(hour=8, minute=30, day_of_week=2)}

C. {'task': 'app.weekly_task', 'schedule': crontab(hour=8, minute=30, day_of_week='tue')}

D. {'task': 'app.weekly_task', 'schedule': crontab(hour=8, minute=30, day_of_week='Monday')}

Solution

1. Step 1: Understand crontab day_of_week format

   Celery's crontab accepts day_of_week as string names like 'mon', 'tue', or integers 0-6 (0=Sunday).

2. Step 2: Evaluate options

   {'task': 'app.weekly_task', 'schedule': crontab(hour=8, minute=30, day_of_week='mon')} uses 'mon' string which is correct. {'task': 'app.weekly_task', 'schedule': crontab(hour=8, minute=30, day_of_week=2)} uses integer 2 which is Tuesday (0=Sunday). {'task': 'app.weekly_task', 'schedule': crontab(hour=8, minute=30, day_of_week='tue')} uses 'tue' string which is Tuesday. {'task': 'app.weekly_task', 'schedule': crontab(hour=8, minute=30, day_of_week='Monday')} uses 'Monday' full name which is not supported.

3. Final Answer:

   {'task': 'app.weekly_task', 'schedule': crontab(hour=8, minute=30, day_of_week='mon')} -> Option A

4. Quick Check:

   Use 'mon' string for Monday in crontab [OK]

Hint: Use three-letter lowercase day names like 'mon' for crontab [OK]

Common Mistakes:

• Using full day names like 'Monday' instead of 'mon'
• Using string numbers like '1' instead of integers or names
• Confusing day_of_week numbering starting at Sunday