def symmetric_difference_update(self, other):
        """
        Throws out all intervals except those only in self or other,
        not both.
        """
        other = set(other)
        ivs = list(self)
        for iv in ivs:
            if iv in other:
                self.remove(iv)
                other.remove(iv)
        self.update(other)
Throws out all intervals except those only in self or other,
        not both.