Re: [Py4j-users] Calling Python from Java side?

[Frank J. I. Jr. <fr...@ae...>]

On 2/17/2015 4:32 AM, Barthelemy Dagenais wrote:
> The process is a little involved so there might be better alternatives
> (jython would probably not work with SciPy. not sure how pyjnius
> handles Java to Python).
Hi Barthelemy,

Thanks for your suggestions, to which I have a few follow-up questions.

But first, do you have any opinions about another possible alternative, 
that is to use Pyrolite?
    https://pythonhosted.org/Pyro4/pyrolite.html
{pyrolite reportedly eliminates the Jython hop earlier required when 
using the following chain:
Java<->Jython<->Pyro<->CPython; so now Java<->pyrolite<->CPython}
....

So if I understand your steps below, they are nearly parallel to your 
example in
http://py4j.sourceforge.net/advanced_topics.html#implementing-java-interfaces-from-python-callback

as follows below, and if so, I might simply first attempt to extend your 
example:

> The steps would be:
>
> 1. In Java, declare an interface (e.g., MySciPy).
> 2. In Java, create a class that will hold an instance of MySciPy. This
> is the class you will use in Java to "talk to Python through MySciPy".
> We will call it PythonProxy with setMySciPy and getMySciPy
> 3. In Python, implement the interface in a class (e.g., MySciPyImpl)

1. MySciPy=interface Operator (Java side)
2. PythonProxy=OperatorExample  (Java side)
     --> "holding instance of 
MySciPy"=OperatorExample.randomBinaryOperator(Operator op)
3. MySciPyImpl=Addition (Python side)

> Then, once you are done, the control flow would be:
> ...
> 4. In Python, call PythonProxy.setMySciPy(myscipyimpl_instance)
> ...
> 6. Your Java code can now call Python with
> PythonProxy.getMySciPy().yourMethodHere()

4.  In Python, call PythonProxy.setMySciPy(myscipyimpl_instance) <=>
    gateway.entry_point.randomBinaryOperator(operator)
OR
   
gateway.jvm.py4j.examples.OperatorExample().randomBinaryOperator(operator)

6.  yourMethodHere() = doOperation()


But now to achieve what I'm seeking, which is your Step 6, I'm still 
mystified but would the following get me close?:

On Step2, in my Java client code, I would also do:
   myOperatorExample = new OperatorExample();
   GatewayServer server = new GatewayServer(myOperatorExample);
      server.start();

so that:

6.  In Java, PythonProxy.getMySciPy().yourMethodHere() <=>
     numbers = myOperatorExample.randomBinaryOperator(Operator.doOperation)

I don't see how the above would bind myOperatorExample to the actual 
Python proxy.


Thanks!





-- 

Frank J. Iannarilli   fr...@ae...
Aerodyne Research, Inc., 45 Manning Road, Billerica, MA 01821 USA