[Tutor] Observer design pattern: request for feedback

[chombee]

Hi,

I decided I wanted to use the Observer design pattern in my application.
I did a little googling, but all the examples that I found of Observer
in Python seemed over-complicated, so I wrote my own simple version. It
doesn't have as many features as other Observer implementations might,
but it's a start. Any critical comments or suggestions would be greatly
appreciated. The code is here:

https://gist.github.com/90d8b7ec425ac92f5539