codepad - http://codepad.org - is an online pastebin. It lets you enter your code, written in Python or one of some other popular languages, into a text box. You then click a button on the page to run the code. Codepad shows the output from the run.
You don't have to register on the site to edit and run code, only to save code. You also get a unique URL for your code, which you can share via chat, email or on your web site or blog.
I tried out Codepad with a simple Python function definition and two calls to it. It worked:
The Codepad site is written in Python using the Pylons web framework and the SQLAlchemy ORM, and some other techniques such as a supervisor and virtual machines, which are of interest too, IMO.
Steven Hazel is the creator of Codepad, and also founder of Sauce Labs, a Selenium testing company.