Purpose

Sister library to the Dispatch project.

Project Maturity

The project has some testing implemented. Testing is done using the pytest framework. Simply navigate to the root directory and execute

py.test

I have verified that serialdispatch works on Python3 in Windows 10, Ubuntu, and on the Raspberry Pi 2 (a Debian distribution) within the curve tracer project.

Quick Usage Notes

Setup

pip install serialdispatch

Initialization

The SerialDispatch object must be created before accessing any of the SerialDispatch methods. On instantiation, SerialDispatch must be supplied with a port which is byte-aligned and has the same methods available as the Python serial library. It is assumed that this will be a serial port; however, there is nothing that would stop it from being any other byte-aligned communications channel that has the same interface.

port = serial.Serial("COM9", baudrate=57600, timeout=0.1)
ps = serialdispatch.SerialDispatch(port)

Subscribing

Subscribing is done using the SerialDispatch.subscribe() function. This function takes two parameters, the topic and the function to associate with the topic. Continuing with the starting code above:

def my_subscriber_function(data):
    print('subscriber executed, received data: ', data)
    
ps.subscribe('foo', my_subscriber_function)
#                           ^ subscribing function
#              ^ topic

After executing the above code, every time that the topic foo is received, the string subscriber executed, received data: will be output to the console along with the received data.

The format of data depends on the format of the data received. If the data received is in the format of a string, then a string is returned. If the data received is a single numerical value, then the numerical value is returned. If the data received is an array of data, then the array is returned in the form of a Python list, and if multiple arrays are returned, then a list of lists is generated.

A list of lists allows us to receive multi-dimensional data within a single message. For instance, if data to be sent was a series of (x, y) coordinates, we get all of the data at once. Note that this must be done from within the callback:

def my_callback(data)
    x, y = data  # split the data into the two expected values

    # now do some stuff with the data...

Publishing

Publishing to a topic is simple, but has to follow a format as well. If you simply want to send a string, you can simply

ps.publish('foo', 'my string')
#                     ^ string
#            ^ topic

This will publish 'my string' to the topic 'foo'.

Using the (x, y) idea once again, the data is in two dimensions.

x = [... some unsigned 8-bit numbers ...]
y = [... some signed 16-bit numbers ...]
ps.publish('xy', [x, y], ['U8', 'S16'])
#                              ^ list of format specifiers
#                  ^ data
#            ^ topic

Strings can only be 1 dimensional. The length of x and y must be the same. The currently-supported format specifiers:

• STRING
• U8
• S8
• U16
• S16
• U32
• S32

More details

You can find more details at for(embed).

Example Usage

There is a working example that demonstrates working with multiple data types within the /examples directory. A quick - but complete - example is shown below.

import serialdispatch

# define your serial port or supply it otherwise
port = serial.Serial("COM9", baudrate=57600, timeout=0.01)

# create a new instance of SerialDispatch
ps = serialdispatch.SerialDispatch(port)

# create your subscribers
def array_subscriber(data):
    # retrieve received data for topic 'bar' and print to screen
    print('data: ', data)

def i_subscriber(data):
    # retrieve received data for topic 'i' and print to screen
    print('i: ', data)

# use the instance of SerialDispatch to associate the subscriber function with the topic
ps.subscribe('bar', array_subscriber)
ps.subscribe('i', i_subscriber)

# publish to topics as desired
while True:
    ''' publish 'a test message', to subscribers of 'foo', note
        that the message must be in a list of lists '''
    ps.publish('foo', 'a test message')
    time.sleep(1.0)

Contributions

To make a contribution, simply fork the repository. Create a branch that is appropriately descriptive of your change and perform your development. When complete, create a pull request using that branch - DO NOT merge into master! Once the proper test coverage is added and passing on TravisCI, then we can merge into the master branch.

In some cases in which the documentation or examples are contributed, this process will be fast-tracked.