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https://github.com/WebThingsIO/webthing-python

Python implementation of a Web Thing server
https://github.com/WebThingsIO/webthing-python

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Python implementation of a Web Thing server

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webthing

========



.. image:: https://github.com/WebThingsIO/webthing-python/workflows/Python%20package/badge.svg

    :target: https://github.com/WebThingsIO/webthing-python/workflows/Python%20package

.. image:: https://img.shields.io/pypi/v/webthing.svg

    :target: https://pypi.org/project/webthing/

.. image:: https://img.shields.io/badge/license-MPL--2.0-blue.svg

    :target: https://github.com/WebThingsIO/webthing-python/blob/master/LICENSE.txt



Implementation of an HTTP `Web Thing `_. This library is compatible with Python 2.7 and 3.5+.



Installation

============



``webthing`` can be installed via ``pip``, as such:



.. code:: shell



  $ pip install webthing



Running the Sample

==================



.. code:: shell



  $ wget https://raw.githubusercontent.com/WebThingsIO/webthing-python/master/example/single-thing.py

  $ python3 single-thing.py



This starts a server and lets you search for it from your gateway through mDNS. To add it to your gateway, navigate to the Things page in the gateway's UI and click the + icon at the bottom right. If both are on the same network, the example thing will automatically appear.



Example Implementation

======================



In this code-walkthrough we will set up a dimmable light and a humidity sensor (both using fake data, of course). Both working examples can be found in the `examples directory `_.



Dimmable Light

--------------



Imagine you have a dimmable light that you want to expose via the web of things API. The light can be turned on/off and the brightness can be set from 0% to 100%. Besides the name, description, and type, a |Light|_ is required to expose two properties:



.. |Light| replace:: ``Light``

.. _Light: https://webthings.io/schemas/#Light



* ``on``: the state of the light, whether it is turned on or off



  - Setting this property via a ``PUT {"on": true/false}`` call to the REST API toggles the light.



* ``brightness``: the brightness level of the light from 0-100%



  - Setting this property via a PUT call to the REST API sets the brightness level of this light.



First we create a new Thing:



.. code:: python



    light = Thing(

        'urn:dev:ops:my-lamp-1234',

        'My Lamp',

        ['OnOffSwitch', 'Light'],

        'A web connected lamp'

    )



Now we can add the required properties.



The ``on`` property reports and sets the on/off state of the light. For this, we need to have a ``Value`` object which holds the actual state and also a method to turn the light on/off. For our purposes, we just want to log the new state if the light is switched on/off.



.. code:: python



  light.add_property(

      Property(

          light,

          'on',

          Value(True, lambda v: print('On-State is now', v)),

          metadata={

              '@type': 'OnOffProperty',

              'title': 'On/Off',

              'type': 'boolean',

              'description': 'Whether the lamp is turned on',

          }))



The ``brightness`` property reports the brightness level of the light and sets the level. Like before, instead of actually setting the level of a light, we just log the level.



.. code:: python



  light.add_property(

      Property(

          light,

          'brightness',

          Value(50, lambda v: print('Brightness is now', v)),

          metadata={

              '@type': 'BrightnessProperty',

              'title': 'Brightness',

              'type': 'number',

              'description': 'The level of light from 0-100',

              'minimum': 0,

              'maximum': 100,

              'unit': 'percent',

          }))



Now we can add our newly created thing to the server and start it:



.. code:: python



  # If adding more than one thing, use MultipleThings() with a name.

  # In the single thing case, the thing's name will be broadcast.

  server = WebThingServer(SingleThing(light), port=8888)



  try:

      server.start()

  except KeyboardInterrupt:

      server.stop()



This will start the server, making the light available via the WoT REST API and announcing it as a discoverable resource on your local network via mDNS.



Sensor

------



Let's now also connect a humidity sensor to the server we set up for our light.



A |MultiLevelSensor|_ (a sensor that returns a level instead of just on/off) has one required property (besides the name, type, and optional description): ``level``. We want to monitor this property and get notified if the value changes.



.. |MultiLevelSensor| replace:: ``MultiLevelSensor``

.. _MultiLevelSensor: https://webthings.io/schemas/#MultiLevelSensor



First we create a new Thing:



.. code:: python



  sensor = Thing(

      'urn:dev:ops:my-humidity-sensor-1234',

      'My Humidity Sensor',

       ['MultiLevelSensor'],

       'A web connected humidity sensor'

  )



Then we create and add the appropriate property:



* ``level``: tells us what the sensor is actually reading



  - Contrary to the light, the value cannot be set via an API call, as it wouldn't make much sense, to SET what a sensor is reading. Therefore, we are creating a **readOnly** property.



    .. code:: python



      level = Value(0.0);



      sensor.add_property(

          Property(

              sensor,

              'level',

              level,

              metadata={

                  '@type': 'LevelProperty',

                  'title': 'Humidity',

                  'type': 'number',

                  'description': 'The current humidity in %',

                  'minimum': 0,

                  'maximum': 100,

                  'unit': 'percent',

                  'readOnly': True,

              }))



Now we have a sensor that constantly reports 0%. To make it usable, we need a thread or some kind of input when the sensor has a new reading available. For this purpose we start a thread that queries the physical sensor every few seconds. For our purposes, it just calls a fake method.



.. code:: python



  self.sensor_update_task = \

      get_event_loop().create_task(self.update_level())



  async def update_level(self):

      try:

          while True:

              await sleep(3)

              new_level = self.read_from_gpio()

              logging.debug('setting new humidity level: %s', new_level)

              self.level.notify_of_external_update(new_level)

      except CancelledError:

          pass



This will update our ``Value`` object with the sensor readings via the ``self.level.notify_of_external_update(read_from_gpio())`` call. The ``Value`` object now notifies the property and the thing that the value has changed, which in turn notifies all websocket listeners.



Adding to Gateway

=================



To add your web thing to the WebThings Gateway, install the "Web Thing" add-on and follow the instructions `here `_.