'Whole set as serializable dictionary.
Example:
>>> s = LimitedSet(maxlen=200)
>>> r = LimitedSet(maxlen=200)
>>> for i in range(500):
...     s.add(i)
>>> r.update(s.as_dict())
>>> r == s
True'

def as_dict(self):

    return {key: inserted for (inserted, key) in values(self._data)}
