**Course Title:** Mastering Flask Framework: Building Modern Web Applications **Section Title:** Real-Time Applications and WebSockets **Topic:** Develop a real-time chat application using Flask-SocketIO.(Lab topic) **Objective:** By the end of this topic, you will be able to develop a real-time chat application using Flask-SocketIO, understand the basics of WebSockets, and learn how to implement real-time communication in your Flask applications. **Prerequisites:** * Familiarity with Flask and its ecosystem * Understanding of WebSockets and real-time communication * Basic knowledge of JavaScript and HTML/CSS **What are WebSockets?** WebSockets are a bi-directional communication protocol that allows real-time communication between a client (usually a web browser) and a server over the web. They enable bidirectional, full-duplex communication, allowing both the client and server to send and receive data at the same time. **Flask-SocketIO:** Flask-SocketIO is a library that provides an easy-to-use interface for building real-time web applications using WebSockets. It allows you to push updates to connected clients in real-time, making it ideal for applications like live updates, live chat, and gaming. **Developing a Real-Time Chat Application using Flask-SocketIO:** ### Step 1: Install Flask-SocketIO ```bash pip install flask-socketio ``` ### Step 2: Create a new Flask application ```python from flask import Flask from flask_socketio import SocketIO, emit app = Flask(__name__) app.config['SECRET_KEY'] = 'secret!' socketio = SocketIO(app) ``` ### Step 3: Define a route for the chat application ```python @app.route('/') def index(): return render_template('index.html') ``` ### Step 4: Define a SocketIO event for handling new messages ```python @socketio.on('new_message') def handle_new_message(message): emit('new_message', message, broadcast=True) ``` ### Step 5: Define a SocketIO event for handling user connections ```python @socketio.on('connect') def handle_connect(): emit('connected', 'You are connected!') ``` ### Step 6: Define a SocketIO event for handling user disconnections ```python @socketio.on('disconnect') def handle_disconnect(): emit('disconnected', 'You are disconnected!') ``` ### Step 6: Run the application ```bash python app.py ``` ### Step 7: Open multiple browser windows and connect to the chat application Open multiple browser windows and navigate to `http://localhost:5000`. Each browser window will establish a WebSocket connection to the server. ### Step 8: Send messages from one browser window to all other connected browser windows In one browser window, type a message in the input field and click the "Send" button. The message will be broadcasted to all other connected browser windows. **Example Use Cases:** * Live updates: Use Flask-SocketIO to push updates to connected clients in real-time, making it ideal for applications like live scores, live updates, and live chat. * Gaming: Use Flask-SocketIO to enable real-time communication between clients and servers, making it ideal for applications like multiplayer games and online gaming platforms. * Real-time collaboration: Use Flask-SocketIO to enable real-time collaboration between users, making it ideal for applications like collaborative document editing and collaborative project management. **Best Practices:** * Use Flask-SocketIO to handle real-time communication between clients and servers. * Use WebSockets to establish bi-directional communication between clients and servers. * Use emit() to send messages from the server to connected clients. * Use broadcast=True to send messages to all connected clients. * Use handle_connect() and handle_disconnect() to handle user connections and disconnections. **Conclusion:** In this topic, you learned how to develop a real-time chat application using Flask-SocketIO, understand the basics of WebSockets, and learn how to implement real-time communication in your Flask applications. You can now use Flask-SocketIO to build real-time web applications and enable bi-directional communication between clients and servers. **Additional Resources:** * Flask-SocketIO documentation: <https://flask-socketio.readthedocs.io/en/latest/> * WebSockets documentation: <https://developer.mozilla.org/en-US/docs/Web/API/WebSockets_API> * Real-time web applications: <https://en.wikipedia.org/wiki/Real-time_web> **Leave a comment or ask for help:** If you have any questions or need help with implementing Flask-SocketIO in your application, please leave a comment below.

pip install flask-socketio

from flask import Flask
from flask_socketio import SocketIO, emit

app = Flask(__name__)
app.config['SECRET_KEY'] = 'secret!'
socketio = SocketIO(app)

@app.route('/')
def index():
    return render_template('index.html')

@socketio.on('new_message')
def handle_new_message(message):
    emit('new_message', message, broadcast=True)

@socketio.on('connect')
def handle_connect():
    emit('connected', 'You are connected!')

@socketio.on('disconnect')
def handle_disconnect():
    emit('disconnected', 'You are disconnected!')

python app.py