Defining Celery tasks in Flask - Mini Project: Build & Apply

Defining Celery Tasks in Flask

📖 Scenario: You are building a Flask web application that needs to perform background tasks without blocking the main app. You will use Celery to define and run these tasks asynchronously.

🎯 Goal: Create a Celery task in a Flask app that adds two numbers and returns the result.

📋 What You'll Learn

Create a Celery instance linked to the Flask app

Define a simple Celery task function

Use the Celery task decorator correctly

Ensure the task can be called asynchronously

💡 Why This Matters

🌍 Real World

Background tasks like sending emails, processing images, or running long computations without blocking the web server.

💼 Career

Many web developer roles require knowledge of asynchronous task queues like Celery to build scalable and responsive applications.

1

Set up Flask app and Celery instance

Create a Flask app instance called app and a Celery instance called celery linked to app with the broker URL set to redis://localhost:6379/0.

Flask

from flask import Flask
from celery import Celery

# Your code here

Need a hint?

Use Flask(__name__) to create the app and pass app.name and broker URL to Celery.

2

Configure Celery task decorator

Add a Celery task decorator to a function called add that takes two parameters x and y.

Flask

from flask import Flask
from celery import Celery

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

# Define the add task below
# Your code here

Need a hint?

Use @celery.task above the function definition to make it a Celery task.

3

Call the Celery task asynchronously

Call the add task asynchronously using the delay method with arguments 4 and 6, and assign the result to a variable called result.

Flask

from flask import Flask
from celery import Celery

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

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

# Call the add task asynchronously
# Your code here

Need a hint?

Use add.delay(4, 6) to call the task asynchronously and assign it to result.

4

Complete the Flask app with a route to trigger the task

Add a Flask route /start-task that triggers the add task asynchronously with 10 and 20, and returns a string with the task id using result.id.

Flask

from flask import Flask
from celery import Celery

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

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

result = add.delay(4, 6)

@app.route('/start-task')
def start_task():
    # Your code here

Need a hint?

Use @app.route('/start-task') to define the route and call add.delay(10, 20) inside the function.