[web2py] Common controller functionality

[Yarin]

I've always liked the idea of controllers as classes, allowing for 
subclassing of controllers, and thereby providing an easy means of handling 
common controller functionality. I'm curious as to why web2py didn't follow 
this approach? Is there a recommended way of handling code that is common 
to a group of controllers (besides sticking it at the top of a controller 
file)?