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Python and Kepler

Details about the Python Actor

Kepler includes the Ptolemy II Python actor that uses Jython,  a Java implementation of Python.

As of November 2011, the Kepler development tree was using Jython 2.5.2, see How to Determine Which Version of Jython is being used.

Kepler has the Python Script actor, which has no ports; to view or edit its Python script, select Configure (or double click on the icon).

See the Ptolemy II PythonScript documentation for details.



External Resources


Mailing List Questions about Python and Kepler

The Kepler-users mailing list has posts about Python and Kepler.  Unfortunately, there is no direct way to search the mailing list archives, we suggest searching for the terms "kepler python".  Below are some post about Python and Kepler:

python and kepler - ideas about interfacing to an external Python interpreter (October, 2011)

Using swing from the Python Actor; skeleton in syspath? - includes information about how Jython searches for packages (March, 2011)

Ideas about creating a new type for the Python tuple type (July, 2009)


How Jython finds imports

See Chapter 8: Modules and Packages for Code Reuse for details, but basically, the Python sys.path variable stores the search path.

See Re: Using swing from the Python Actor; skeleton in syspath? for a Ptolemy model that prints the contents of the sys.path variable and discussion about a bug.  In November, 2011, that model was checked in to the Ptolemy II tree as ptolemy/actor/lib/python/test/PythonSysPath.xml.

In my default Ptolemy setup, sys.path was:


In November, 2011, the Kepler devel tree was updated with outreach/workflows/demos/Python/PythonImport.xml.  That model reads a Jython module in ptolemy/src/lib/Lib/

  1. Start a development version of Kepler, and open outreach/workflows/demos/Python/PythonImport.xml
    Right click on the PythonScript actor, select Configure and note that jythonClassName is set to "PtPythonSquare"
  2. Double click on the PythonScript actor and be sure that the script looks like:
    import PtPythonSquare
    PtPythonSquare = reload(PtPythonSquare)
  3. The Jython model to be run is at ptolemy/src/lib/Lib/  Note that you may need to create the Lib/ directory.  Note that the first lib directory starts with a lower case el and the second starts with an uppercase el.  Jython uses the Jython sys.path variable to find modules.  To get the value of sys.path, either:
    • Right click on the PythonScript actor, select "Listen to Actor", run the model and look at the value printed on stdout


    • Run the model at $PTII/ptolemy/actor/lib/python/test/PythonSysPath.xml
      The contents of should be:
    class Main :
      def fire(self) :
      token = self.input.get(0)
  4. Run the model, note that the output is the square of the input.
  5. Edit and change
  6. Run the model again, note that the output is the twice the input.


Note that the python.home Java property controls what the location of the Python home directory.  In Ptolemy, try:


java -classpath $PTII:${PTII}/lib/jython.jar -Dpython.home=/tmp/bar ptolemy.vergil.VergilApplication PythonSysPath.xml

The two types of Python Actors in Ptolemy II

Kepler uses Ptolemy II as its execution engine.  Ptolemy II includes two different types of Python Actors.  In the Ptolemy II vergil configuration, under More Libraries -> Python, there are two actors:

  • PythonActor - Right click and select Open Actor and an editor appears that contains the Python contents of the actor
  • PythonScript - Double click and an editor appears that contains the Python contents of the actor


By default, Kepler is shipped with the 2nd actor, PythonScript.


Both actors actually use the Java class  The PythonActor merely has a _tableauFactory set in

the configuration.  ptolemy/actor/lib/python/python.xml contains xml that sets the _tableauFactory.


When the user drags a PythonActor in, the _tableauFactory is set.

How to determine what version of Jython is being used

As of November 5, 2011, the Kepler development tree uses Jython-2.5.2.  The easiest way to determine this is to look at the size of jython.jar.  If jython.jar is 10mb, then Jython-2.5.2 is being used.   If jython.jar is around 1Mb, then Jython-2.2 or 2.2.1 is being used.

Kepler-2.2 uses Jython-2.2 or 2.1

The Kepler ptolemy/src/lib/jython.jar file comes from the Ptolemy II tree file $PTII/lib/jython.jar
In October, 2011, the changelog for the jython.jar file in the Ptolemy II tree at $PTII/lib/jython.jar is below:

r62357 | cxh | 2011-11-05 11:05:34 -0700 (Sat, 05 Nov 2011) | 1 line

Upgraded to Jython-2.5.2.
r60529 | cxh | 2011-03-10 13:14:39 -0800 (Thu, 10 Mar 2011) | 1 line

Revert to jython (presumably) 2.2 because jython2.5.8 does not have org.python.core.PyJavaInstance
r60525 | cxh | 2011-03-10 07:22:55 -0800 (Thu, 10 Mar 2011) | 1 line

Updated to jython 2.5.2
r48715 | cxh | 2008-03-12 16:18:19 -0700 (Wed, 12 Mar 2008) | 2 lines

Updated jython.jar to a standalone version so that the javaos Jython package could be found.  See ptolemy/actor/lib/python/test/auto/PythonReadFile.xml

r48497 | cxh | 2008-02-18 16:16:18 -0800 (Mon, 18 Feb 2008) | 2 lines

Updated to Jython 2.2.1

r46882 | cxh | 2007-09-17 08:08:28 -0700 (Mon, 17 Sep 2007) | 2 lines

Updated to Jython 2.2

r32050 | liuxj | 2004-03-25 17:58:35 -0800 (Thu, 25 Mar 2004) | 2 lines

recompiled to work with j2sdk 1.5.0

r27667 | cxh | 2003-04-30 20:41:06 -0700 (Wed, 30 Apr 2003) | 2 lines


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