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Object Persistence db_save error

Take the following class. Why can't I use db_save to store an instance of this class? The reason I am using this class instead of just a set is because I will eventually derive this class from RingElement rather than SageObject, because I'm looking to create a Ring of Sets.

class FakeSet(SageObject):
    def __init__(self,_set):
        self.values = _set
        self.iterator = self.__iter__()
        if self.values != set():
    def __iter__(self):
        for this_entry in self.values:
            yield this_entry
    def get_set(self):
        return self.values
    def __repr__(self):
        return str(list(self.values))
    def __getattr__(self,attr):
        return getattr(self.values,attr)

Then I enter:

sage: fake = FakeSet([1,2,3])
sage: print fake
sage: db_save(fake,"test")

to which the interpreter responds:

Traceback (click to the left of this block for traceback)
cPickle.PicklingError: Can't pickle <type 'generator'>: attribute
lookup __builtin__.generator failed