[Zope] using the Session Data Object hooks

[Dennis Allison]

The Session Data Object exposes the Transience Interfaces 

setDelNotificationTarget(self, f )

and 

setAddNotificationTarget(self, f)

which register f to be called when a session object is added or deleted. The 
registered function is supposed to accept a single argument, item, the object
being added or removed.

So, how does one write a PythonScript to do this?  Or must it be an External 
Method and/or a product Extension?  It should be straightforward enough as 
it's part of the normally exposed interface.