Python Web Thing Wrapper

The webthing module, associtated with the Things Gateway from Mozilla, is a Python 3 module implementing the Web of Things (WoT) API. It enables Python modules to speak to systems that communicate via the WoT protocol.

The webthing module is written from a reference implementation written in Javascript. The style and idioms of Javascript are markedly different from those in the Python world. Working directly with webthing requires a shift in thinking away from what would be a more common forms found in many Python modules.

This pywot module wraps webthing in a more Pythonic interface. This makes for shorter, easier to read programs.

This project is an experiment. It is meant as an educational tool giving an example on how someone could make a full featured Web of Thing API for Python. This project may not be maintained beyond my blog posts that use it as an example.

directory structure

/demo/ - several examples of the API
/pywot/ - the code for pywot

API Reference

WoTThing

class pywot.WoTThing(config, name, type_, description)

An object derived from the base class webthing.Thing representing a device or virtual device. As a class, it provides services for further derived classes, focusing on reconciling webthing.Properties with the Python property method. Further derived classes may define Properties at class load time rather than during object initialization time. This facilitates modification of property values by simplifying the syntax:

# using the webthing API directly:
my_weather_station.get_thing().properties['temperature'].value.notify_of_external_update(32)
# the same thing using the pywot API
my_weather_station.temperature = 32

Derived classes also get an automatically generated asynchronous polling loop to fetch a value from some external source. The derived class only needs to define an asynchronous method to fetch the value once and pass it to the pywot.WoTThing.wot_property classmethod when defining a property.

class WeatherStation(pywot.WoTThing):

    async def get_weather_data(self):
        async with aiohttp.ClientSession() as session:
            async with async_timeout.timeout(config.seconds_for_timeout):
                async with session.get(config.target_url) as response:
                    self.weather_data = json.loads(await response.text())
        self.temperature = self.weather_data['current_observation']['temp_f']
    
    temperature = pywot.WoTThing.wot_property(
        'temperature',
        initial_value=0.0,
        description='the temperature in ℉',
        value_source_fn=get_weather_data,
        units='℉'
    )

The WoTThing class requires configuration of only one value, the loop delay during polling. That is supplied to the __init__ method in the form config.seconds_between_polling. This is library uses the configman package for propagating configuration from command-line, configuration files or the environment to object constructors.

Each instance of pywot.WoTThing requires a name and description, unrestricted strings. The type_ parameter is for a string from the list at: https://iot.mozilla.org/wot/#web-thing-types, for most things that aren't switches or bulbs, 'thing' is likely the best option.

WoTThing.wot_property

pywot.WoTThing.wot_property(kls, *, name, initial_value, description, value_source_fn=None, value_forwarder=None, **kwargs )

This classmethod works much like the Python property method. It defines a webthing.Property for the enclosing derived class of pywot.WoTThing. name and description are unrestricted strings. initial_value will be used to both set the value and the type of the value for the property. value_source_fn is a reference to an asynchronous method of the derived class that will be periodically run to update the value of the property. None means no polling is necessary for this property. value_forwarder is a reference to a function that will set a value to any underlying hardware when a new value is assigned to a property. metadata is a Mapping of extra data that the UI can interpret use to help display or represent the value. Possible values for the underlying 'webthing' API are unclear.

WoTServer

class pywot.WoTServer(config, things, name=None, port=80, ssl_options=None)

This class derives from pything.WebThingServer and cooperates with the pywot.Thing class to provide a polling loop method compatible with the underlying tornado Web server. When the server's run method is executed, each pywot.Thing instance gives its list of value updating tasks to the server. The server then queues them all into the asynchronous event loop.

things is an iterable of instances of pywot.Thing. name is a unrestricted string. port is the port onwhich to offer HTTP services. ssl_options is unclear from the underlying webthing documentation.

WoTServer.run

pywot.WoTServer.run()

This instance method of pywot.WoTServer handles starting and shutdown all the asynchronous value updating methods and the Web server. It is a blocking call that can be terminated with the signal SIG_TERM or ^C from the command line.

logging_config

pywot.logging_config

This is an instance of a Namespace object from the configman configuration system. It holds configuration information used to initialize the logging system. It is offered as a convenience.

log_config

pywot.log_config

This is a module level method that will take an instance of completed configman compatible configuration and just stream it out to logging at INFO level. It is just a convenience if configman is employed in apps using this package.