How do you write a Code Generator for Antlr?

I want to make a Python Code Generator.

Yes, I know, there is already an initial version of one, but I can't understand what it's doing.

As far as I understand (which is not that far ;)), you need to override class CodeGenerator. Is this all that is needed?

It will be great of someone can point me to some documentation that says exactly how to write a Code Generator.

Thanks.

Anteater