.. _python-reacting-to-events:

Making a Python module - Reacting to events
===========================================



Here we want the robot say 'Hello, you' every time it detects a human face.

To do this, we need to subscribe to the 'FaceDetected' event, raised by the
ALFacedetection module.

If you read the documentation of :cpp:func:`ALMemoryProxy::subscribeToEvent`, you will see
you need a module name and the name of a callback.

So we need to write a NAOqi module in Python.

To create a module in Python, we also need a broker.

The example can be found below.


.. seealso::

   - :ref:`naoqi-overview`


:download:`reacting_to_events.py </examples/python/reacting_to_events.py>`

.. literalinclude:: /examples/python/reacting_to_events.py
   :language: py


Few notes:

* Make sure to use a global variable for the module instance.

* Make sure the name you pass to the constructor of ALModule matches
  the name of your variable.

* The method of your class are automatically transform into bound
  methods, **providing that you wrote a doc string** for this method,
  and it **does not start with an underscore**.


.. code-block:: python

  class MyModule:

    # This method will be bound:
    def myMethod(self):
      """ does this and that """
      pass

    # This will NOT be bound:
    def myMethod(self):
      if foo:
        pass

    # This will also NOT be bound
    def _myMethod(self):
      pass



* Once you have built a ALBroker object, you need to keep the object alive
  for the subscribing to work, hence the ``while(True)`` loop.
  You also need the broker object to be alive in order to create proxies
  without specifying an IP or a port.

* The script must be run with ``--pip`` and ``--pport`` options to work.


Run the script, and put your face in front of the robot : you should hear
'Hello, you'.