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What is a correct way to pickle an object from a class with slots, when this object references itself through one of its attributes? Here is a simple example, with my current implementation, which I'm not sure is 100 % correct: import weakref import pickle class my_class(object): __slots__ = ('an_int', 'ref_to_self', '__weakref__') def __init__(self): self.an_int = 42 self.ref_to_self = weakref.WeakKeyDictionary({self: 1}) # How to best write __getstate__ and __setstate__? def __getstate__(self): obj_slot_values = dict((k, getattr(self, k)) for k in self.__slots__) # Conversion to a usual dictionary: obj_slot_values['ref_to_self'] = dict(obj_slot_values['ref_to_self']) # Unpicklable weakref object: del obj_slot_values['__weakref__'] return obj_slot_values def __setstate__(self, data_dict): # print data_dict for (name, value) in data_dict.iteritems(): setattr(self, name, value) # Conversion of the dict back to a WeakKeyDictionary: self.ref_to_self = weakref.WeakKeyDictionary( self.ref_to_self.iteritems()) This can be tested for instance with: def test_pickling(obj): "Pickles obj and unpickles it. Returns the unpickled object" obj_pickled = pickle.dumps(obj) obj_unpickled = pickle.loads(obj_pickled) # Self-references should be kept: print "OK?", obj_unpickled == obj_unpickled.ref_to_self.keys()[0] print "OK?", isinstance(obj_unpickled.ref_to_self, weakref.WeakKeyDictionary) return obj_unpickled if __name__ == '__main__': obj = my_class() obj_unpickled = test_pickling(obj) obj_unpickled2 = test_pickling(obj_unpickled) Is this a correct/robust implementation? how should __getstate__ and __setstate__ be written if my_class inherited from a class

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