wxpython treectrl

 (child, cookie) = self.tree.GetFirstChild(root) 

            while child.IsOk(): 

                (child, cookie) = self.tree.GetNextChild(root, cookie) 

If you call GetNextChild() when there is no next child, it's not an 
> error --- you just get back an invalid TreeItemId. 
>   child.IsOk() == False

http://wxpython-users.1045709.n5.nabble.com/TreeListCtrl-and-its-edit-control-td2325959.html