Brython, Python in your browser:
Brython is designed to replace Javascript as the scripting language for the Web. As such, it is a Python 3 implementation, adapted to the HTML5 environment, that is to say with an interface to the DOM objects and events.
That is a trip. Practical? Probably not. Definitely neat though.
The brython.js code that does all the heavy lifting is only 175,936 bytes.