If you would like to learn the Python programming language, then this is the perfect app for you. You can type python scripts into your iPhone or iPad, and execute them-on-the-fly, in order to see the results. All this without the need to have access to your computer, or requiring a webserver.
This is a great way to try out the code examples that you read in books, or on the web.
The app features syntax highlighting, and can save and load your work to your phone.