Sorry I wasn't clear enough. The Singleton is a design pattern from the Gang of Four book that fits this situation well. It is a class that is meant to control access to the one and only instance of a global variable. I was just using that as a frame of reference, though; Zope has no such class for the Application object, or I wouldn't be writing this message.
Oh, ok, sorry, hard to tell intent from actual code. :-)
I just need some way of getting at the one and only Application object at run-time. Something like:
from Globals import app myOb = app.Control_Panel.Products.MyProduct.MyZClass('foo') ...
Given a reference to an object in the ZODB, I can do this via:
app = self.getPhysicalRoot() myOb = app.Control_Panel.Products.MyProduct.MyZClass('foo')
But, this does not work from methods like __init__, or __setstate__, where we do not have a physical location in the ZODB, yet.
Ah, I see the problem. I'm afraid I don't know the answer. I generally use the manage_afterAdd and manage_beforeDelete methods to do things like this. I suppose you could pass the root object into the constructor. __setstate__... well. Err... Anybody else?