If you are using KDE (I don't know much about gnome.), there are superkaramba widgets, which are written in python. Here is the main website where you can find a simple tutorial:
Here is the website where people post their superkaramba applets:
There is also plasma, written in C++:
and here are links to plasmoids:
Plasma is for KDE 4+ where superkaramba works for KDE3+. Plasmoids are new. Last time I checked their website there was still nothing about their API. If you want to learn C++ on top of your python I would recommend plasma. But as I said there is not much documentation. You can start with someone else's plasmoid and modify it for your needs.
Superkaramba is also good. I actually learned python by writing a superkaramba applet.