Decorator for parameter listeners.

        .. note::

            There is no way to remove a listener added with this decorator. Use
            :py:func:`add_attribute_listener` if you need to be able to remove
            the :py:func:`listener <remove_attribute_listener>`.

        The callback function is invoked only when the parameter changes.

        The callback arguments are:

        * ``self`` - the associated :py:class:`Parameters`.
        * ``attr_name`` - the parameter name. This can be used to infer which parameter has triggered
          if the same callback is used for watching multiple parameters.
        * ``msg`` - the new parameter value (so you don't need to re-query the vehicle object).

        The code fragment below shows how to get callbacks for the ``THR_MIN`` parameter:

        .. code:: python

            @vehicle.parameters.on_attribute('THR_MIN')
            def decorated_thr_min_callback(self, attr_name, value):
                print " PARAMETER CALLBACK: %s changed to: %s" % (attr_name, value)

        See :ref:`vehicle_state_observing_parameters` for more information.

        :param String attr_name: The name of the parameter to watch (or '*' to watch all parameters).
        :param args: The callback to invoke when a change in the parameter is detected.

def on_attribute(self, attr_name, *args, **kwargs):
        """
        Decorator for parameter listeners.

        .. note::

            There is no way to remove a listener added with this decorator. Use
            :py:func:`add_attribute_listener` if you need to be able to remove
            the :py:func:`listener <remove_attribute_listener>`.

        The callback function is invoked only when the parameter changes.

        The callback arguments are:

        * ``self`` - the associated :py:class:`Parameters`.
        * ``attr_name`` - the parameter name. This can be used to infer which parameter has triggered
          if the same callback is used for watching multiple parameters.
        * ``msg`` - the new parameter value (so you don't need to re-query the vehicle object).

        The code fragment below shows how to get callbacks for the ``THR_MIN`` parameter:

        .. code:: python

            @vehicle.parameters.on_attribute('THR_MIN')
            def decorated_thr_min_callback(self, attr_name, value):
                print " PARAMETER CALLBACK: %s changed to: %s" % (attr_name, value)

        See :ref:`vehicle_state_observing_parameters` for more information.

        :param String attr_name: The name of the parameter to watch (or '*' to watch all parameters).
        :param args: The callback to invoke when a change in the parameter is detected.

        """
        attr_name = attr_name.upper()
        return super(Parameters, self).on_attribute(attr_name, *args, **kwargs)