'Add a listener callback on a particular parameter.
The callback can be removed using :py:func:`remove_attribute_listener`.
.. note::
The :py:func:`on_attribute` decorator performs the same operation as this method, but with
a more elegant syntax. Use ``add_attribute_listener`` only if you will need to remove
the observer.
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 example below shows how to get callbacks for the ``THR_MIN`` parameter:
.. code:: python
#Callback function for the THR_MIN parameter
def thr_min_callback(self, attr_name, value):
print " PARAMETER CALLBACK: %s changed to: %s" % (attr_name, value)
#Add observer for the vehicle\'s THR_MIN parameter
vehicle.parameters.add_attribute_listener(\'THR_MIN\', thr_min_callback)
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 add_attribute_listener(self, attr_name, *args, **kwargs):

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