Access a Java object at runtime in Jep-embedded Python

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Tongfei Chen

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Mar 15, 2017, 1:53:26 AM3/15/17
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Suppose I have a Jep instance running in my Java main method.
I'd like to pass an object (not a class) from the JVM side to the Python side, so in Python I can call the methods of this object dynamically. Is this possible?


Ben Steffensmeier

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Mar 16, 2017, 3:25:59 PM3/16/17
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Yes, Jep lets you use java objects easily from python, here is a simple example:

try (Jep jep = new Jep()){
    Object javaObject = new Object();
    jep.set("javaObject", javaObject);
    jep.eval("print(javaObject.toString())");
}



On Wed, Mar 15, 2017 at 12:53 AM, Tongfei Chen <cton...@gmail.com> wrote:
Suppose I have a Jep instance running in my Java main method.
I'd like to pass an object (not a class) from the JVM side to the Python side, so in Python I can call the methods of this object dynamically. Is this possible?


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Tongfei Chen

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Mar 18, 2017, 9:18:17 PM3/18/17
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Thanks a lot !


On Thursday, March 16, 2017 at 3:25:59 PM UTC-4, Ben Steffensmeier wrote:
Yes, Jep lets you use java objects easily from python, here is a simple example:

try (Jep jep = new Jep()){
    Object javaObject = new Object();
    jep.set("javaObject", javaObject);
    jep.eval("print(javaObject.toString())");
}


On Wed, Mar 15, 2017 at 12:53 AM, Tongfei Chen <cton...@gmail.com> wrote:
Suppose I have a Jep instance running in my Java main method.
I'd like to pass an object (not a class) from the JVM side to the Python side, so in Python I can call the methods of this object dynamically. Is this possible?


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Nathan Jensen

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May 18, 2018, 11:38:43 AM5/18/18
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Python imports are weird (in my opinion).  Back a few messages, you got an ImportError on "import java.util.ArrayList".  That doesn't work but a similar statement of "from java.util import ArrayList" does work.  You can notice the same behavior with other python packages, for example "import numpy.ndarray" fails but "from numpy import ndarray" succeeds.  You can play with these imports with the jep command line script, though it will use the default ClassEnquirer (though that will include classes on the classpath).

Java packages with io are a mess because there is a Python module named io.  https://github.com/ninia/jep/issues/29

What does your import statement look like?  If you're doing import io.knowscieng.SomeClass instead of from io.knowscieng import SomeClass that may explain the problem.




On Fri, May 18, 2018 at 5:35 AM, SemanticBeeng <semanticbeen...@gmail.com> wrote:

As per https://groups.google.com/d/msg/jep-project/uuMVFAKhIY0/vih6VDceCQAJ I implemented `ClassEnquirer`

```
    val ci = ClassList.getInstance()

    new JepConfig()
...
      /**
        * A way to be able to execute Python code embedded in the Knowscieng code base (se python folders)
        * #resource
        */
      .addIncludePaths(PythonPaths.includePaths: _*)
      .setClassEnquirer(new ClassEnquirer {
        override def isJavaPackage(name: String): Boolean = {
          if (ci.isJavaPackage(name)) {
            logger.info(s"isJavaPackage($name) = true")
            true
          }
          else if (name.startsWith("java.") || name.startsWith("io.knowscieng.")) {
           logger.info(s"isJavaPackage($name) = true")
            true
          }
          else {
           logger.info(s"isJavaPackage($name) = false")
            false
          }
        }

```
Now I am getting 

```
18/05/18 03:26:13 [jep-single-thread-19] INFO orchestration: isJavaPackage(y_module.data_layer) = false
 18/05/18 03:26:13 [jep-single-thread-19] INFO orchestration: isJavaPackage(y_module.data_layer.module) = false
 18/05/18 03:26:13 [jep-single-thread-19] INFO orchestration: isJavaPackage(signal) = false
 18/05/18 03:26:13 [jep-single-thread-19] INFO orchestration: isJavaPackage(_signal) = false
 18/05/18 03:26:13 [jep-single-thread-19] INFO orchestration: isJavaPackage(enum) = false
 18/05/18 03:26:13 [jep-single-thread-19] INFO orchestration: isJavaPackage(logging) = false
 18/05/18 03:26:13 [jep-single-thread-19] INFO orchestration: isJavaPackage(time) = false
 18/05/18 03:26:13 [jep-single-thread-19] INFO orchestration: isJavaPackage(traceback) = false
 18/05/18 03:26:13 [jep-single-thread-19] INFO orchestration: isJavaPackage(linecache) = false
 18/05/18 03:26:13 [jep-single-thread-19] INFO orchestration: isJavaPackage(tokenize) = false
 18/05/18 03:26:13 [jep-single-thread-19] INFO orchestration: isJavaPackage(re) = false
 18/05/18 03:26:13 [jep-single-thread-19] INFO orchestration: isJavaPackage(sre_compile) = false
 18/05/18 03:26:13 [jep-single-thread-19] INFO orchestration: isJavaPackage(_sre) = false
 18/05/18 03:26:13 [jep-single-thread-19] INFO orchestration: isJavaPackage(sre_parse) = false
 18/05/18 03:26:13 [jep-single-thread-19] INFO orchestration: isJavaPackage(sre_constants) = false
 18/05/18 03:26:13 [jep-single-thread-19] INFO orchestration: isJavaPackage(copyreg) = false
 18/05/18 03:26:13 [jep-single-thread-19] INFO orchestration: isJavaPackage(token) = false
 18/05/18 03:26:13 [jep-single-thread-19] INFO orchestration: isJavaPackage(warnings) = false
 18/05/18 03:26:13 [jep-single-thread-19] INFO orchestration: isJavaPackage(string) = false
 18/05/18 03:26:13 [jep-single-thread-19] INFO orchestration: isJavaPackage(_string) = false
 18/05/18 03:26:13 [jep-single-thread-19] INFO orchestration: isJavaPackage(threading) = false
 18/05/18 03:26:13 [jep-single-thread-19] INFO orchestration: isJavaPackage(atexit) = false
 18/05/18 03:26:13 [jep-single-thread-19] INFO orchestration: isJavaPackage(pandas) = false
 18/05/18 03:26:13 [jep-single-thread-19] INFO orchestration: isJavaPackage(pyspark) = false
 18/05/18 03:26:13 [jep-single-thread-19] ERROR data_layer: Error initModule(data_layer) <class 'ModuleNotFoundError'>: No module named 'io.knowscieng'; 'io' is not a package  In = 303102866, using List(/projects/knowscieng.io/.../src/main/python)

```
The import from the python code is for classes from "io.knowscieng".

But the inquirer is not even asked.
So seems to be confused by the includePaths?

Thanks
Nick


On Friday, May 18, 2018 at 6:09:41 AM UTC-4, SemanticBeeng wrote:
Hi Ben,

Another question in this context, please.

Have a Scala program calling a python script it works fine.
Now need to pass more custom Scala objects to the script running embedded .

Passing a java map works.

But trying to "import java.util.ArrayList" in Python gives " <class 'ModuleNotFoundError'>: No module named 'java.util.ArrayList' "

Have examples where starting a python script (not embeeded in Je) can import and call java objects.
But how to do same from Python running embedded

What I really want is to pass custom Scala objects to embedded Python but also import same classes from Python.

But seeing that passing java maps works without imports I am wondering what is the role of the import.

Is the solution around setting class loaders in JepConfig?

Many thanks in advance,
Nick


On Thursday, March 16, 2017 at 3:25:59 PM UTC-4, Ben Steffensmeier wrote:
Yes, Jep lets you use java objects easily from python, here is a simple example:

try (Jep jep = new Jep()){
    Object javaObject = new Object();
    jep.set("javaObject", javaObject);
    jep.eval("print(javaObject.toString())");
}


On Wed, Mar 15, 2017 at 12:53 AM, Tongfei Chen <cton...@gmail.com> wrote:
Suppose I have a Jep instance running in my Java main method.
I'd like to pass an object (not a class) from the JVM side to the Python side, so in Python I can call the methods of this object dynamically. Is this possible?


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For more options, visit https://groups.google.com/d/optout.

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