What is Python Banyan?

Python Banyan is a lightweight, reactive framework used to create flexible, non-blocking, event-driven, asynchronous applications. It was designed primarily to aid in implementing real-time physical computing applications for devices such as the Raspberry Pi, ESP8266, and Arduino. Still, it may easily be applied to projects outside of the physical programming domain.

Banyan uses a publish/subscribe model similar to MQTT but is much faster than MQTT in real-time control and data monitoring applications. A benchmark comparison of Banyan and MQTT is provided later in this guide to illustrate Banyan's efficiency. If your application requires connectivity to an MQTT broker, a Gateway is provided.

Most traditional physical computing libraries or frameworks use an object-oriented model that yields a single, tightly coupled, monolithic executable image. Python Banyan uses an extension of the object-oriented model, called the component-based service-oriented architectural model. A component-based application consists of a set of independent, loosely coupled components. For python-banyan, these components communicate with one another through a set of platform-independent, user-defined protocol messages transmitted over a TCP network.

A Banyan application is composed of a set of components running concurrently as separate processes. These components can be developed using a single language platform such as Python, or developed using any of the other Banyan frameworks. There are versions of Banyan available for JavaScript, Ruby, and Java. Components developed using dissimilar languages can be combined without modification to form a single, cohesive application.

Banyan uses a central message distribution mechanism called the Backplane. When first starting a Banyan application, the Backplane is brought on-line, followed by the application's components. At startup, each component automatically "plugs" itself into the Backplane establishing a TCP/IP communication channel between itself and the Backplane.

After communication is established, components may publish messages to the Backplane, receive messages from other components, or both publish and receive messages. A major feature of Python Banyan is that it can incorporate Numpy data into a protocol message seamlessly and effortlessly.

Without modification, a Banyan application's components can run on a single computer or distributed across multiple computers. These configurations will be demonstrated later on in this document.

A Little More Detail About Python Banyan

Banyan Base Classes

All Banyan components are created by inheriting from one of the supplied Banyan base classes. The base class methods are overridden as needed to support the component's specific needs.

The base classes act as a wrapper for the ZeroMQ embeddable networking library that has been configured to operate in a Publish/Subscribe networking pattern. Also, the base class encodes and decodes protocol messages for efficient network transmission, using MessagePack.

Banyan Protocol Messages

Banyan protocol messages consist of 2 parts, a "topic" and a "payload."

The Topic String

A message topic consists of a simple string. For a component to receive messages with a set of given topics, a component subscribes to receive messages for each topic. A subscribing component receives all messages published containing the desired topic.

Prefix Matching

When a message is received, the topic is compared to the subscribed topic. If it matches, the message is placed on the component's receive queue. Any topic that begins with the subscribed topic string is considered a match even if the received message topic contains additional text. For example, if you subscribe to the topic "abcd," and a message is received with a topic of "abcde," the "abcde" message will be placed on the receive queue. Any messages with topics that begin with the subscribed topic string are considered a match even though the topic may contain additional text.

The Message Payload

Message payloads consist of a Python dictionary type structure, containing one or more name/value items. By utilizing a dictionary, message data can be quickly de-referenced and processed.

Because Banyan messages are not computer language-specific, components written in other computer languages, such as JavaScript, can be used within a Python Banyan application. A simple JavaScript demo is provided as one of the included examples.

Where Is Python Banyan Being Used?

Commercially, Python Banyan has been chosen by Palace Games in San Francisco to monitor and control their Palace Games Edison Room. The Edison room contains several hundred sensors and actuators. Banyan helps tie all the devices and their associated micro-controllers together, allowing them to communicate quickly and transparently. Banyan supports data transfers of Numpy data, which the Edison room uses to model their data efficiently. You can read about Palace Games on the Raspberry Pi Blog.

Banyan is also being used in numerous physical computing projects utilizing the Raspberry Pi, Arduino, and ESP8266. An earlier version of Python Banyan, called razmq, was used to control a Raspberry Pi robot.

Banyan Application Design

When designing a Banyan Component, it is good practice to keep it as small as possible. By limiting a component to a small area of concern, testing is greatly simplified, and the potential for component reuse increases.

Some Design Guidelines

A component should subscribe to the minimal number of message topics as possible.
Keep messages as short as possible.
Limit the component to its task at hand. For example, if you wish to log application activity, create a specific logging component. All other components can take advantage of this logging facility in a consistent fashion. It also offloads logging I/O from the main component, promoting higher performance for the system as a whole.