Calling tasks asynchronously in Flask - Mini Project: Build & Apply

Calling tasks asynchronously in Flask

📖 Scenario: You are building a simple Flask web app that needs to perform a long task without making the user wait. To do this, you will call the task asynchronously.

🎯 Goal: Build a Flask app that starts a background task asynchronously when a user visits a route, so the app stays responsive.

📋 What You'll Learn

Create a Flask app instance

Define a long-running task function

Call the task asynchronously using threading

Create a route that triggers the async task and returns immediately

💡 Why This Matters

🌍 Real World

Web apps often need to perform slow tasks like sending emails or processing files without making users wait. Calling tasks asynchronously keeps the app responsive.

💼 Career

Understanding asynchronous task handling in Flask is important for backend web developers to build efficient and user-friendly web applications.

1

Set up the Flask app and import threading

Import Flask from flask and Thread from threading. Then create a Flask app instance called app.

Flask

# Import Flask and Thread
# Create Flask app instance called app
# Your code here

Need a hint?

Use from flask import Flask and from threading import Thread. Then create app = Flask(__name__).

2

Define a long-running task function

Define a function called long_task that simulates a long task by importing time and calling time.sleep(5) inside the function.

Flask

from flask import Flask
from threading import Thread

app = Flask(__name__)

# Define long_task function that sleeps for 5 seconds
# Your code here

Need a hint?

Define def long_task(): and inside it call time.sleep(5) to simulate delay.

3

Call the long task asynchronously

Inside the Flask app, create a route /start-task using @app.route('/start-task'). In the route function called start_task, start long_task asynchronously using Thread(target=long_task).start() and return the string 'Task started' immediately.

Flask

from flask import Flask
from threading import Thread
import time

app = Flask(__name__)

def long_task():
    time.sleep(5)

# Create /start-task route that starts long_task asynchronously
# Your code here

Need a hint?

Use @app.route('/start-task') to define the route. Inside start_task, call Thread(target=long_task).start() and return 'Task started'.

4

Add the app run command

Add the code to run the Flask app by checking if __name__ == '__main__' and calling app.run(debug=True).

Flask

from flask import Flask
from threading import Thread
import time

app = Flask(__name__)

def long_task():
    time.sleep(5)

@app.route('/start-task')
def start_task():
    Thread(target=long_task).start()
    return 'Task started'

# Add app run command below
# Your code here

Need a hint?

Add if __name__ == '__main__': and inside it call app.run(debug=True) to start the server.