PythonPubSub

Python Pub/Sub - Example 11

This example is a reimplementation of example 2 in Python.

pypub.py

This example combines both features (subscriber and publisher into one file). Let's start with publishing.

gn = GravityNode()
while gn.init("PyPub") != gravity.SUCCESS:
    SpdLog.warn("failed to init, retrying...")
    time.sleep(1)
gn.registerDataProduct("PythonGDP", gravity.TCP)
gn.subscribe("PythonGDP", mySub) # Note that this is here to subscribe only. Not useful for publishing

counterPB = BasicCounterDataProductPB()
gdp = GravityDataProduct("PythonGDP")
for i in range (1, 50):
    counterPB.count = i
    gdp.data=counterPB
    gn.publish(gdp)
    time.sleep(1)

gn.waitForExit()

To set up the subscriber, you must define a class the same way you would in C++. Then, call the subscribe method with an instantiation of that class.

class MySubscriber(GravitySubscriber):
    # We're only using GravitySubscriber here, but this is generally the way we 
    # initialize Gravity Python components to ensure that __init__ is called
    # on each parent.
    def __init__(self):
        GravitySubscriber.__init__(self)

    def subscriptionFilled(self, dataProducts):
        counterPB = BasicCounterDataProductPB()
        for gdp in dataProducts:
            gdp.populateMessage(counterPB)
            SpdLog.warn("received counter with value = "+str(counterPB.count))

mySub = MySubscriber()

gn = GravityNode()
while gn.init("PyPub") != gravity.SUCCESS:
    SpdLog.warn("failed to init, retrying...")
    time.sleep(1)
gn.registerDataProduct("PythonGDP", gravity.TCP) # Not useful for subscribing.
gn.subscribe("PythonGDP", mySub)

Once you understand the regular C++ version, this is pretty straightforward.

Again it's pretty similar to the C++ version. One difference is that the _init_() method is explicitly defined, which ensures parent constructors are called. Another is constants, such as GravityReturnCodes and protocols.