Re: [Jython-dev] Attempting to embed Jython

[Stephen S. <ss...@ci...>]

Robert,

Thanks.  I had finally found this distinction.  The problem I was having was that I need to
generate the code for later execution.  I have found (as you point out) that I can compile for
execution or for eval and later execute the code with the same result.

I appreciate the reply.

-steve

"Robert W. Bill" wrote:

> Hi Stephen,
>
> On Thu, 31 May 2001, Stephen Schleimer wrote:
> > Folk,
> >
> > I am attempting to embed  Jython in a system whose dynamic configuration
> > is to include Jython expressions and code fragments.  These code
> > fragments are runtime evaluated and effect the progress of the overall
> > system.   The fragments serve as statement guards, iterators, etc.
> > Thus, I need to do a good deal of expression evaluation, examine, in
> > Java, the results of the evaluation and proceed.  Not every expression
> > will naturally set a variable in the environment storing its results.
> > Thus, I would like to be able to determine the value of the evaluated
> > expression without resorting to a storage side effect .
> >
> > The public interfaces to Py (such as runCode) return a value.  However,
> > in the way I have been experimenting with them, the value is always
> > PyNone.  In addition, a printed result of the expression evaluation is
> > delivered to sysout.
> >
> > I am looking, therefore, for a couple of things:
> >
> > 1) reliably suppressing delivery of the computed result of the
> > expression to sysout
> > 2) reliably delivering the computed result to the invoker of the
> > expression evaluation.
> >
> > Any aid is appreciated.
>
> I'm probably misunderstanding this, but I think you could use the
> PythonInterpreter instance to eval and exec things.
>
> If the code fragments are statement/assignment-free, you can use
> interp.eval(fragment) which returns a PyObject.
>
> If statements/assignments exist in the fragments, you can use
> interp.exec(someFunnyVar = fragment); then
> PyObject x = PyObject.get("someFunnyVar").
>
> Both ways `reliably' get values from the interpreter and neither prints to
> stdout unless there is a print statement in the fragment.
>
> Here's an example of eval'ing and exec'ing things and getting objects
> from the interpreter in case it helps. I'm not sure I really understand
> your situation, so complain lots if I'm way off base.
>
> //====file: test.java
> import java.util.Properties;
> import org.python.core.*;
> import org.python.util.*;
>
> class test {
>     static PythonInterpreter interp;
>
>     public static void main(String[] args) {
>         Properties props = new Properties();
>         props.setProperty("python.home", "/home/rbill/jython-2.1a1");
>         PythonInterpreter.initialize(System.getProperties(), props, new String[0]);
>         interp = new PythonInterpreter();
>
>         // If you truly just need to evaluate, use this
>         PyObject i = interp.eval("1 and 0 or 2");
>         System.out.println( i );
>
>         // If you write eval'able fragments, return value are automatic.
>         // Here's another that processes this code file for lines
>         // containing "eval", plus does some other wacky stuff just to
>         // show how much can be done in an eval().
>         i = interp.eval("filter(lambda x: x.find('eval') > -1, [x.strip()[:-1] for x in " +
>                         "open('test.java').readlines() if not x.lstrip().startswith('//')])");
>         System.out.println(i);
>
>         // If eval doesn't cut it,and you really need statements, you
>         // could assign the results of your fragments to a variable in the
>         // interpreter and extract it.
>         interp.exec("import sys; __frag_val = sys.path");
>         PyObject p = interp.get("__frag_val");
>         System.out.println(p);
>     }
> }
>
> cheers,
> Robert
>
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