jython-dev

[Jython-dev] Attempting to embed Jython

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

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.

Response by E-mail would also be appreciated.

Thanks

-steve

Re: [Jython-dev] Attempting to embed Jython

[Robert W. B. <rb...@di...>]

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

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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