---
title: "Tornado"
url: https://docs.catalyst.zoho.com/en/serverless/help/appsail/help-guides/python/tornado/
description: "Catalyst AppSail is a fully-managed PaaS component of Catalyst Serverless that enables you to develop and deploy services in Java, Node.js, and Python in the cloud with ease, and manage your platform instances."
last_updated: 2025-11-03T10:48:29Z
service: Serverless
type: general
---

# Tornado Framework

[Tornado](https://www.tornadoweb.org/en/stable/) is a Python web framework and an asynchronous networking library that relies on non-blocking network I/O to serve web applications. This framework is therefore ideal for handling a large number of active server connections, such as in websockets. Tornado also offers built-in internalization, quick request execution, and many other features.

This example illustrates the steps to build a simple Python app with the Tornado framework. This application will then be bundled and associated with an AppSail service, and deployed to the console.

1. Create a new folder in your local system for the Tornado app.

2. Navigate to the directory from your terminal and execute the following command to install Tornado:

```python
python3 -m pip install tornado -t.
```

3. You can now create your python index file and name it `app.py` or anything of your choice. Add the logic you require in the application's code. Given below is a sample code for a basic "Hello World" program.

```python
import os
import tornado.ioloop
import tornado.web
class MainHandler(tornado.web.RequestHandler):
    def get(self):
        self.write("Hello, World!")
if __name__ == "__main__":
    app = tornado.web.Application([
        (r"/", MainHandler),
    ])
    listen_port = int(os.getenv('X_ZOHO_CATALYST_LISTEN_PORT', 9000))
    app.listen(listen_port, address='0.0.0.0')
    tornado.ioloop.IOLoop.current().start()
```

4. You can now [initialize an AppSail service](https://docs.catalyst.zoho.com/en/cli/v1/initialize-resources/initialize-appsail/) in the same directory from the CLI or [add it](https://docs.catalyst.zoho.com/en/cli/v1/add-appsail/) in an existing project directory. The app's source must be your application's directory. Provide the following value while initializing the app service:

    **Stack**: Python_3_9

5. Ensure all the Python application files along with the `tornado` modules are present in the build directory you specify during initialization. Catalyst will automatically ZIP your app files during deployment to the remote console. 

6. [Deploy the app service](https://docs.catalyst.zoho.com/en/cli/v1/deploy-resources/deploy-appsail//) to the console.   

7. You can then configure the [startup command](https://docs.catalyst.zoho.com/en/serverless/help/appsail/key-concepts/appsail-execution/#startup-commands) given below from the console:

```python
python3 -u app.py
```

You can also configure this in the `app-config.json` file before deploying.

Access the deployed app service from its [endpoint URL](https://docs.catalyst.zoho.com/en/serverless/help/appsail/key-concepts/appsail-execution/#custom-domain-url).