Python Interpreter ?

AFAIK, there is no way to reasonable way to reset python. It wasn't designed for such a situation. Suggesting an approach will depend a little on what you're trying to achieve, and how much 'state' you really need to reset. If you're running idle, it may be sufficient to save your code into a file and re-run it each time.

Rather than storing your variables and functions as globals you could also just store them in a dictionary which could be cleared when required.

The previous approach can be automated with the use ofcompile, exec* and eval functions to dynamically build and run code. These functions give you the choice to pass in a dictionary containing variables. Instead of using the default value of locals and globals you can setup a dictionary that contains your 'global' variables and functions which will be visible to your script.

I'm more than willing to post some code examples if you think that will help