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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 _state_changed(self, previous_state, new_state):
 """Callback called whenever the underlying Receiver undergoes a change of state. This function wraps the states as Enums to prepare for calling the public callback. :param previous_state: The previous Receiver state. :type previous_state: int :param new_state: The new Receiver state. :type new_state: int """

        try:
            try:
                _previous_state = constants.MessageReceiverState(previous_state)
            except ValueError:
                _previous_state = previous_state
            try:
                _new_state = constants.MessageReceiverState(new_state)
            except ValueError:
                _new_state = new_state
            if _previous_state == constants.MessageReceiverState.Opening \
                    and _new_state == constants.MessageReceiverState.Error:
                _logger.info("Receiver link failed to open - expecting to receive DETACH frame.")
            elif self._session._link_error:  # pylint: disable=protected-access
                _logger.info("Receiver link ATTACH frame invalid - expecting to receive DETACH frame.")
            else:
                self.on_state_changed(_previous_state, _new_state)
        except KeyboardInterrupt:
            _logger.error("Received shutdown signal while updating receiver state from {} to {}".format(
                previous_state, new_state))
            self._error = errors.AMQPClientShutdown()