Several home automation platforms support Python as an extension, but if you’re a real Python fiend, you’ll probably want Home Assistant, which places the programming language front and center. Paulus Schoutsen created Home Assistant in 2013 “as a simple script to turn on the lights when the sun was setting,” as he told attendees of his recent Embedded Linux Conference and OpenIoT Summit presentation, “Automating your Home with Home Assistant: Python’s Answer to the Internet of Things.”

Schoutsen, who works as a senior software engineer for AppFolio in San Diego, has attracted 20 active contributors to the project. Home Assistant is now fairly mature, with updates every two weeks and support for more than 240 different smart devices and services. The open source (MIT license) software runs on anything that can run Python 3 — from desktop PCs to a Raspberry Pi, and counts thousands of users around the world.

Like most automation systems, Home Assistant offers mobile and desktop browser clients to control smart home devices from afar. It differs from most commercial offerings, however, in that it has no hub appliance, which means there are no built-in radios. You can add precisely which radios you want, however, using USB sticks. There’s also no cloud component, but Schoutsen argues that any functionality you might sacrifice because of this is more than matched by better security, privacy, and resiliency.

“There is no dependency on a cloud provider,” said Schoutsen. “Even when the Internet goes down, the home doesn’t shut down, and your very private data stays in your home.”

Schoutsen did not offer much of a promo in his presentation, but quickly set to work explaining how the platform works. Since Home Assistant is not radically different from other IoT frameworks — one reason why it interfaces easily with platforms ranging from Nest to Arduino to Kodi — the presentation is a useful introduction to IoT concepts.

To get a better sense of Home Assistant’s strengths, I recently asked Schoutsen for his elevator pitch. He highlighted the free, open source nature of the software, as well as the privacy and security of a local solution. He also noted the ease of setup and discovery, and the strength of the underlying Python language.

“Python makes it very easy to extend the system,” Schoutsen told me. “As a dynamic language, it allows a flexibility that Java developers can only dream off. It is very easy to test out and prototype new pieces on an existing installation without breaking things permanently. With the recent introduction of MicroPython, which runs on embedded systems as Arduino and ESP8266, we can offer a single language for all levels of IoT: from sensors to automation to integration with third-party services.”

In Schoutsen’s ELC 2016 presentation, he described how Home Assistant is an event-driven program that incorporates a state machine that keeps track of “entities” — all the selected devices and people you want to track. Each entity has an identifier, a state condition, and attributes. The latter describes more about the state, such as the color and intensity of the light on a Philips Hue smart bulb.

To integrate a Philips Hue into the system, for example, you would need to use a light “component,” which is aware of the bulb and how to read its state (off or on). Home Assistant offers components for every supported device or service, as well as easy access to component groups such as lights, thermostats, switches, and garage doors. Setup is eased with a network discovery component that scans the network, and if you have a supported device, sets it up automatically. 

The software is further equipped with a service registry, which provides services over the event bus. “We can register the turn-on command for a light, and have it send an email or SMS,” said Schoutsen. “A timer can send a time change event every second, and a component can ask to be notified at a particular time, or in intervals. Based on time change events, it will trigger the callback of the components.”

Each component writes its state to the state machine, emitting a state change event to the event bus. “The light component would register its turn on service inside the service registry so that anyone could fire an event to the event bus to turn on the light,” said Schoutsen.

You can easily integrate a light component with a motion detector component using an automation component. This would listen to the motion detector events, and fire a “turn light on” event to the event bus, which in turn would be forwarded to the service registry. The registry would then check to see that the light component can handle the event. “Automation components can listen for events, observe certain attribute states or triggers, and act on them,” explained Schoutsen.

Another component type handles presence detection. “The platform can check the router to see which phones are connected in order to see who is home,” said Schoutsen. “Other components are responsible for recording event and state history, or for entity organization — grouping multiple entities and summarizing their state.” Components are available for integrating third party services, such as MQTT or IFTTT, and other components export data to external databases and analysis tools.

Schoutsen also explained concepts such as a “platform” layer that sits above the entity components. Each platform integrates an “abstract base class,” which “acts as the glue between the real device and the one represented in Home Assistant,” said Schoutsen. Later, he ran through a code example for a basic switch and explored the use of trigger zones for geofencing.

As Schoutsen says, Home Assistant is “gaining a lot of traction.” Check out the complete video below to see what happens when Python meets IoT.

Interested in sharing your expertise, knowledge and ideas on embedded Linux and IoT with the open source community? Embedded Linux Conference + OpenIoT Summit Europe 2016 will be held on October 11-13 in Berlin, Germany. The call for speaking proposals is open until June 26, 2016. Submit your proposal now!