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

[Tom Parris]

Rick,

Thanks!  This is very helpful.  I'll read the Ptolemy document more
thoroughly and try again.

The basic challenge I'm having is translating from java examples to python.
I've been experimenting with the optional methods.   In the Java examples
I've been looking at (e.g., Repeat, DownSample) the constructor method is
used to: create and set parameters, and sets the input_tokenConsumptionRate
and output_tokenConsumptionRate.  The same is true for SDFTranformer (from
which these examples are subclassed). That is what led me to try the same in
Python (with the __init__ method).

The other challenge I'm having is reading n elements from an input port, but
only consuming m elements (where 0<=m<=n) in order to implement sliding
window actors.  Given the code for IOPort.java, I'm not convinced this is
even possible. It looks (to the untrained eye) that every call to get
implicitly pops tokens off the channel.

I'll work both challenges some more and get back to you offline if I still
need help.

-- Tom

On Tue, Nov 24, 2009 at 11:04 AM, Rick Moore <rem63 at cornell.edu> wrote:

>  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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