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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def parent(self, parent):
 """Setter for the parent state of the state element :param rafcon.core.states.state.State parent: Parent state or None """

        if parent is None:
            self._parent = None
        else:
            from rafcon.core.states.state import State
            assert isinstance(parent, State)

            old_parent = self.parent
            self._parent = ref(parent)

            valid, message = self._check_validity()
            if not valid:
                if not old_parent:
                    self._parent = None
                else:
                    self._parent = ref(old_parent)

                class_name = self.__class__.__name__
                if global_config.get_config_value("LIBRARY_RECOVERY_MODE") is True:
                    do_delete_item = True
                    # In case of just the data type is wrong raise an Exception but keep the data flow
                    if "not have matching data types" in message:
                        do_delete_item = False
                        self._parent = ref(parent)
                    raise RecoveryModeException("{0} invalid within state \"{1}\" (id {2}): {3}".format(
                        class_name, parent.name, parent.state_id, message), do_delete_item=do_delete_item)
                else:
                    raise ValueError("{0} invalid within state \"{1}\" (id {2}): {3} {4}".format(
                        class_name, parent.name, parent.state_id, message, self))