Unlocking the Power of PyScript: A Guide to Running Python Code in Your HTML

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Are you looking for a way to add more interactivity and functionality to your websites? Do you want to incorporate machine learning or data analysis capabilities without relying on external APIs or libraries?

Look no further than PyScript, a revolutionary tool that allows you to run Python code directly in your HTML files. In this guide, we will explore the basics of PyScript, showcase some of its powerful features, and provide tips and best practices for using it effectively in your web development projects.

Common Use Cases for PyScript in Web Development

PyScript’s versatility and capabilities make it a valuable asset for an array of web development projects. Here are some of the common use cases where PyScript excels:

Data Analysis and Visualization

PyScript enables developers to seamlessly integrate Python’s data analysis and visualization libraries into web applications, such as NumPy and Matplotlib. This empowers developers to present data-driven insights visually engaging and interactively.

Machine Learning Applications

With the increasing prominence of machine learning, PyScript offers a powerful platform for integrating Python-based machine learning models into web applications. Developers can provide real-time predictions and personalized experiences to users.

Interactive Games and Simulations

Python’s simplicity and readability make it an attractive choice for game development. PyScript allows developers to create interactive games and simulations, elevating user engagement and entertainment on web pages.

Server-Side Processing

PyScript can also be leveraged for server-side processing, where Python code runs on the server to handle complex tasks and data manipulation. This optimizes the performance of web applications and enhances user experiences.

Getting Started with PyScript

Before we dive into the nitty-gritty details of PyScript, let’s first cover how to get started with it. Installing PyScript is relatively straightforward, and there are several methods to do so:

  • Using npm: Open your terminal and run the following command: npm install pyscript. This will download and install PyScript globally on your system.
  • Using yarn: Run the following command in your terminal: yarn global add pyscript. This will also download and install PyScript globally on your system.
  • Manual installation: Download the PyScript package from the official GitHub repository and follow the manual installation instructions provided there.
  • Once you have installed PyScript, you can start using it in your web development projects by simply adding the <script> tag to your HTML file, along with the PyScript library:
        <title>My Website</title>
        <script src="https://cdn.jsdelivr.net/npm/pyscript@4.0.6/dist/pyscript.min.js"></script>

Understanding PyScript Basics

Now that we have covered how to get started with PyScript, let’s closely examine its core concepts and how they work together.

At its heart, PyScript is a JavaScript library that bridges Python and JavaScript, allowing developers to call Python functions and modules directly within their web pages. Here are some key points to understand about PyScript:

  • Python scripts: These are the actual Python files that contain the logic and functionality you want to execute on your web page. You can write these scripts using any text editor, including any valid Python code, including imports, functions, and classes.
  • JavaScript integration: Once you have written your Python script, you must integrate it into your HTML file using JavaScript. This involves creating a <script> tag that references the PyScript library and includes your Python script as a string.
  • Calling Python functions: To call your Python functions from within your web page, you need to use the py Script object and specify the name of your function. For example, suppose you have a Python function named add_numbers that takes two arguments and returns their sum. To call this function from JavaScript, you would use the py object as follows:
    <!DOCTYPE html>
        <title>PyScript Example</title>
        <!-- Include the PyScript library -->
        <script src="pyscript.js"></script>
            // Call the Python function using PyScript
            var result = py.add_numbers(5, 10);
            console.log(result); // This will print the sum (15) to the browser console

In this example, the py object bridges JavaScript and Python, allowing you to call Python functions from within your JavaScript code. The add_numbers function is called with arguments 5 and 10, and the function call (15) result is stored in the variable result.

  • Handling return values: When you call a Python function from JavaScript, you can handle the return values like any other JavaScript function call. You can assign the result to a variable or use it directly in your JavaScript code.
  • Data exchange: PyScript enables data exchange between Python and JavaScript. You can pass data from JavaScript to Python functions as arguments and receive data from Python functions back into JavaScript as return values.
  • Error handling: When calling Python functions from JavaScript, it’s essential to handle potential errors gracefully. If an error occurs in the Python code, it will be caught by PyScript, and you can handle it using try-catch blocks in JavaScript.
  • Python module support: Besides calling Python functions directly, PyScript also allows you to import and use Python modules in your web pages. This lets you leverage existing Python libraries and functionality within your JavaScript code.

It’s important to note that PyScript requires both Python and JavaScript environments to be set up properly. The Python environment should have installed the required libraries and modules, and the PyScript library should be properly referenced in your HTML file.

Overall, PyScript provides a powerful way to combine the strengths of both Python and JavaScript in web development, allowing developers to leverage Python’s rich ecosystem and JavaScript’s versatility for building interactive and dynamic web applications.

Getting Started with PyScript

To demonstrate using PyScript in a real-life project, let’s consider a simple web application that performs sentiment analysis on user-provided text using a pre-trained Python machine learning model.

We will integrate PyScript into the project to handle the sentiment analysis tasks on the client side, sending the text data to Python for analysis and displaying the results back to the user.

We’ll use Flask as the Python web framework for server-side implementation for this example.


  • Install Flask and PyScript.
  • Download a pre-trained sentiment analysis model (e.g., using libraries like nltk or scikit-learn).

Project Structure:

- sentiment_analysis_app/
  |-- static/
      |-- pyscript.js
  |-- templates/
      |-- index.html
  |-- app.py
  |-- sentiment_model.py


# sentiment_model.py
# Assuming you have a pre-trained sentiment analysis model
def analyze_sentiment(text):
    # Your code to analyze sentiment using the model
    # Return the sentiment (positive, negative, neutral) as a string
    return "positive"  # Replace this with the actual sentiment result


<!-- templates/index.html -->

<!DOCTYPE html>
    <title>Sentiment Analysis App</title>
    <h1>Sentiment Analysis App</h1>
    <textarea id="text-input" rows="4" cols="50" placeholder="Enter text for sentiment analysis"></textarea>
    <button onclick="analyzeSentiment()">Analyze</button>
    <p id="result"></p>

    <script src="{{ url_for('static', filename='pyscript.js') }}"></script>
        function analyzeSentiment() {
            var text = document.getElementById("text-input").value;

            // Call the Python function using PyScript
                .then(function(result) {
                    document.getElementById("result").innerText = "Sentiment: " + result;
                .catch(function(error) {
                    console.error("Error occurred during sentiment analysis:", error);


from flask import Flask, render_template
from pyscript import PyScript
from sentiment_model import analyze_sentiment

app = Flask(__name__)
pyscript = PyScript(app)

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

def analyze_sentiment(text):
    return analyze_sentiment(text)

if __name__ == '__main__':


You can find the latest version of PyScript from the official PyScript repository or package manager.

Running the Application

  • Save the above files in their respective directories.
  • Make sure you have Flask and PyScript installed in your Python environment.
  • Download or create a pre-trained sentiment analysis model and update sentiment_model.py accordingly.
  • Run the Flask application using python app.py.
  • Access the web application at
  • Enter some text in the textarea and click the “Analyze” button to see the sentiment analysis result.

In this example, we used PyScript to integrate Python code (the analyze_sentiment function) into a simple sentiment analysis web application.

The web application runs on Flask and uses PyScript to call the Python function analyze_sentiment from the client-side JavaScript.

The Python function analyzes the sentiment of the user-provided text and returns the result to be displayed back to the user on the web page.

This example highlights the ease of using PyScript to seamlessly integrate Python functionality into web applications, making it a powerful tool for real-life projects involving Python and JavaScript integration.

When To Use PyScript

  • Data Analytics and Visualization

Interactive Data Visualization Dashboards – A financial services company wants to create an interactive dashboard for their clients to view and analyze their investment portfolios. They want to use Python for data manipulation and visualization but also need to deploy the application on the web. With PyScript, they can write the Python code once and run it in the browser, creating an interactive and responsive dashboard that updates in real time as the user interacts with it.

  • Machine Learning Models

Time Predictions and Recommendations – An e-commerce website wants to provide personalized product recommendations to its customers based on their browsing history and purchase behavior. They can use PyScript to deploy machine learning models written in Python directly in the browser, generating real-time recommendations that update as the customer navigates the site.

  • Game Development

Browser-Based Games with Complex Logic – A game development studio wants to create a multiplayer online game with complex logic and calculations. They can use PyScript to write the game’s core logic in Python, then deploy it in the browser using PyScript. This approach allows them to focus on developing the gameplay and user experience rather than worrying about the underlying technology.

  • Scientific Computing and Simulations

Interactive Science Applications – A research institution wants to create an interactive science application for exploring complex scientific phenomena, such as climate modeling or molecular dynamics. They can use PyScript to deploy Python codes for these simulations directly in the browser, allowing users to interact with the models in real-time and gain insights into the underlying physics and mathematics.

  • Education and Training 

Interactive Code Lessons and Tutorials –  A coding bootcamp or online education platform that wants to create interactive lessons and tutorials for teaching programming concepts, such as data structures or algorithm design. They can use PyScript to deploy Python codes for these lessons directly in the browser, allowing students to work through exercises and get immediate feedback on their progress.


PyScript is a powerful tool that allows developers to run Python code directly in their HTML files, seamlessly integrating front-end and back-end development. With PyScript, developers can leverage the strengths of both Python and JavaScript to create robust, scalable, and maintainable web applications.

The guide provided in this document has covered the basics of PyScript, including installation, basic syntax, and advanced features. We have also discussed some real-world use cases for PyScript, highlighting its potential for a variety of applications, from data analytics and machine learning to game development and educational projects.

As the web development landscape continues to evolve, PyScript is poised to play a significant role in shaping the future of the web. With its ability to combine the power of Python and JavaScript, PyScript offers a unique and compelling solution for developers looking to push the boundaries of what is possible on the web.

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