software design question

[Jorge Godoy]

On Sunday 08 February 2004 01:24 John Roth wrote in
<102bb30d5422pd4 at news.supernews.com>:

> I suspect you've got the callback logic backwards. The basic
> layering pattern is "call down, notify up," and it's the upper
> layer's responsibility to request the notification.
> 
> To explicate: the GUI module calls the domain
> module for service. It also calls the domain module
> to register callbacks, passing the function that it
> want's called.
> 
> When the domain layer has something it wants to
> tell the GUI layer, it simply runs a (possibly empty)
> list of callback functions.

Can you exemplify it?

I'm very interested on such approach and I'm going to read a little
more about it, but examples in Python would help a lot. 


TIA,
-- 
Godoy.     <godoy at ieee.org>