[kepler-users] 3 Qs re: PythonScript, tokenConsumptionRate, portparameters, and polymorphism

[Rick Moore]

Tom,

I ran your workflow and both ports had the correct values ... but your 
script doesn't currently do anything with the blocksize except print it 
to stdout (which in kepler is the console). And that works as well.

A PythonActor doesn't communicate with it's scripts through the standard 
Python __init__ method. Rather it expects the Python scripts to 
implement the same methods that a Java actor might implement. Of course, 
you already use fire(), but there are several other optional methods 
available :

def preinitialize(self) ... set port types and/or scheduling information ...
def initialize(self) ... initialize local variables ...
def prefire(self) ... determine whether firing should proceed ... a good 
place to check whether the execution environment is valid
      if you use it, it must return True to proceed,  False if there is 
some problem ... no return value is the same as False
      the fire(0 method will be called only if prefire() returns True
def postfire(self) ... update persistent state and/or determine whether 
firing should continue to next iteration
     if you use it, it must return True to proceed,  False if there is 
some problem ... no return value is the same as False
     returning False will terminate the workflow
def wrapup(self) ... cleanup and display final results ...
     I use this to reset to the initial state after the last iteration

Designing actors is discussed in detail in chapter 5 of the document at
http://www.eecs.berkeley.edu/Pubs/TechRpts/2008/EECS-2008-28.pdf

If you want, I can help you in more detail off list.

Rick Moore
Information Science
Cornell University

"Once in a while you will be shown the light in the strangest of places, 
if you look at it right"
from Scarlet Begonias by the Grateful Dead

Tom Parris wrote:
> Dear Keplerites:
>
> I have been making steady progress understanding how to write actors 
> for Kepler using the PythonScript actor.  However, I have hit a 
> stumbling block in my attempts to set input_tokenConsumptionRate.  
>
> To illustrate my problem, I have attached a simple workflow with an 
> actor titled "IntTokenSum" written with the PythonScript actor.  This 
> actor is designed to add some number of integer tokens from it's 
> "input" port.  The number of tokens is defined by the "windowsize" 
> port.  The number of tokens to consume with each "fire" is defined 
> with the "blocksize" port.   The current version works as desired with 
> the exception of the blocksize input prot (it always takes on the 
> value of the windowsize input port).
>
> Q1: As the script is currently configured, the windowsize parameter 
> works as advertised.  However, I can't seem to get the blocksize 
> parameter to work.  I've tried a number of approaches to setting the 
> input_tokenConsumptionRate per the java code for several actors (e.g., 
> DownSample).  But now I'm wondering if that is the correct approach. 
>  Perhaps its the call to self.input.get that needs to be changed.  
> Correct output on Display2 should be the sequence: 1, 3, 5, 7, 9, 11, 
> 13, 15, 17.
>
> Q2: I'd also like to use an actor along these lines under the SDF 
> director with portparameters for windowsize and blocksize.  But can't 
> figure out how to to this with the PythonScript actor.  Is this 
> possible?  If so, I would welcome guidance.
>
> Q3: Finally, it should be fairly easy to make this actor polymorphic. 
>  I think this can be done by changing the line:
>
>    val = val + it.intValue()
>
> to
>
>    val = it.add(val)
>
> But I am not sure how to initialize val to the additive identity 
> (generalized notion of zero).
>
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