Python Chat App Tutorial: Build an End-to-End Messaging System

In this tutorial, we will create a fully functional messaging system using Python. We will explore various libraries and technologies to build a real-time chat application from scratch. By the end of this tutorial, you will have a working Python chat app that can be extended and customized as needed.

Table of Contents

  1. Requirements and Setup
  2. Creating the Server
  3. Creating the Client
  4. Running the Chat Application
  5. Conclusion and Next Steps

Requirements and Setup

Before we begin, ensure that you have the following installed on your computer:

  • Python 3.6 or higher
  • A Python code editor (e.g., PyCharm, Visual Studio Code, or Sublime Text)

Next, we will install the necessary libraries for our chat application. Open your terminal or command prompt and run the following command:

pip install socketio flask

This command will install the Socket.IO library for real-time communication and the Flask web framework for serving the chat interface.

Creating the Server

Let's start by creating the server for our chat application. Create a new Python file called and add the following code:

import os
from flask import Flask, render_template
from flask_socketio import SocketIO

app = Flask(__name__)
app.config['SECRET_KEY'] = os.environ.get('SECRET_KEY') or 'secret_key'
socketio = SocketIO(app)

def index():
    return render_template('index.html')

def handle_message(data):
    print(f'Received message: {data}')
    socketio.emit('message', data)

if __name__ == '__main__':

This code sets up a basic Flask application with Socket.IO integration. The index function serves the chat interface, while the handle_message function listens for incoming messages and broadcasts them to all connected clients.

Creating the Client

Now, let's create the client-side interface for our chat application. In the same directory as, create a new folder called templates, and inside that folder, create a new HTML file called index.html. Add the following code:

<!DOCTYPE html>
<html lang="en">
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Python Chat App</title>
    <script src=""></script>
        document.addEventListener('DOMContentLoaded', () => {
            const socket = io();
            const messageInput = document.getElementById('message-input');
            const messageForm = document.getElementById('message-form');
            const messages = document.getElementById('messages');

            socket.on('message', (data) => {
                const item = document.createElement('li');
                item.textContent = data;

            messageForm.addEventListener('submit', (event) => {
                socket.emit('message', messageInput.value);
                messageInput.value = '';
    <h1>Welcome to the Python Chat App!</h1>
    <ul id="messages"></ul>
    <form id="message-form">
        <input id="message-input" type="text" placeholder="Type your message here...">
        <button type="submit">Send</button>

This code sets up a basic chat interface with an input field for messages and a list for displaying received messages. The JavaScript code handles sending messages to the server and displaying incoming messages from other clients.

Running the Chat Application

Now that we have our server and client in place, it's time to test our chat application. Open your terminal or command prompt, navigate to the directory containing, and run the following command:


This command will start the Flask development server. Open your web browser and visit http://localhost:5000 to access the chat interface. Open multiple browser windows or tabs to simulate multiple clients and test the real-time messaging functionality.

Conclusion and Next Steps

Congratulations! You have successfully built a real-time chat application using Python, Flask, and Socket.IO. This basic implementation can be extended and customized with features like user authentication, private messaging, and chat room support. Keep exploring and enhancing your Python chat app to make it even more robust and feature-rich!

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