[Pythonmac-SIG] Getting None in KVC objectInKeyAtIndex_

[David Hain]

I'm trying to use bindings to hook up my model to an NSOutlineView,  
and I'm attempting to use the countOf<Key>, objectIn<Key>AtIndex_  
methods to do the KVC half. The problem I'm running into is that I'm  
getting None for the index argument, and I can't figure out what to do  
with that. The reference materials[1] say that the method corresponds  
to the NSArray objectAtIndex: method, which takes an NSUInteger, but  
doesn't mention anything about null or nil or whatever it is in objc- 
land.

So the question is, is the view supposed to be giving me None for that  
argument, or did I hook something up in IB (or elsewhere) incorrectly?  
If None is expected, then how am I supposed to interpret that? What  
should I return?

Here's a paraphrase of my model:

class Node(NSObject):
     ...

     def countOfChildren(self):
         return len(self.children)

     def objectInChildrenAtIndex_(self, index):
         return self.children[index]

If other information or code would be helpful, I'd be happy to provide  
it. Thanks!

-David


[1]: http://developer.apple.com/documentation/Cocoa/Conceptual/KeyValueCoding/Concepts/AccessorConventions.html