cat.py

class Category(ContextBySpec):
    __name__= None
    __collection__ = __parent__ = 'categories'
    def __init__(self, request, path_segments=None, **kwd):
        super(ContextBySpec, self).__init__(self, request, **kwd)
        for k,v in kwd.items():
            setattr(self, k, v)
        if not path_segments:
            path_segments = request.path_info.split('/')
        self.__name__ = path_segments.pop(0)
        self._remainder = path_segments[1]
        self.request = request
        self.find = request.db[__collection__].find

    def __getitem__(self, name):
        try:
            cursor = self.find({'__name__' : name,
                                '__parent__' : self.__name__})
            assert cursor.count() == 1
            cat = cursor.next()
            return Category(self.request, 
                            path_segments = self._remainder,
                            __parent__ = self.__name__)
        except AssertionError as e:
            ##handle error
            pass

    def __iter__(self):
        try:
            cursor = self.find({"__parent__" : self.__name__})
            return (Category(self.request, 
                             path_segments=self._remainder,
                             __parent__ = self.__name__) for cat in cursor)
        except:
            ##handle errors
            pass