Set up a directory structure on your local computer that looks like this:

SpinLast/
├── getSessionKey.py
├── SpinLast.py
└── static/
    ├── styles.css
└── templates/
    ├── index.html
    └── submit.html

Sign up for a Last.fm API account and record your Last.fm API Key and Shared Secret somewhere safe.

Edit the getSessionKey.py file to include your API Key and Shared Secret.

From the command line, navigate to the SpinLast directory and run getSessionKey.py and follow it's instructions to get your permanent Last.fm Session Key.

Edit the SpinLast.py file to include your API Key, Shared Secret, and Session Key.

From the command line, navigate to the SpinLast directory and run the SpinLast.py application.

Visit the self-hosted website at http://localhost:5000/ and submit any Spinatron URL (like https://spinitron.com/KXLU/) to start scrobbling automatically.

The application will continue running and the webpage will display the most recently scrobbled track as the Spinitron playlist plays in real time.