How to access a python class through PythonInterpreter

Question

I have a pretty simple python class that preprocesses some files, after which I want to read those files into java. The Python class looks like this

class Preprocess(object):
  dataFolder = None
  prepFolder = None

  def __init__(self, dataFolder, prepFolder):
    self.dataFolder = dataFolder
    self.prepFolder = prepFolder

  def preprocess(self):
    *Do some complex preprocess shizzle*

Intuitively I would type something like this.

public class Main {
  public static void main(String[] args) {
    String dataFolder,prepFolder;
    PythonInterpreter py = new PythonInterpreter();
    PyClass prep = new PyClass("Preprocess",new PyString(dataFolder),new PyString(prepFolder));
    prep.callMethod("preprocess");
  }
}

Now this obviously doesn't work. How would I have to use the PythonInterpreter for this to work?

smac89 · Accepted Answer · 2015-01-04 20:32:37Z

To make it less complicated, I find it easier to do as much as possible in PythonInterpreter local namespace then when the need arises, use the __tojava__ method to get a java representation. So with the help of the interpreter, you are able to do something like:

PythonInterpreter py = new PythonInterpreter();
String dataFolder,prepFolder;
py.execfile("filename.py");
py.set("df", dataFolder);
py.set("pf", prepFolder);
py.exec("prep = Preprocess(df, pf)");

//if the preprocess method does not return anything, you can do:
py.exec("prep.preprocess()");

//To get the return value in java, you can do:
SomeJavaClass retvalue = py.eval("prep.preprocess()").__tojava__(SomeJavaClass.class);

//To get and store the return type in the python local namespace:
py.exec("retValue = prep.preprocess()");

There are many other ways of doing the same thing because the PythonInterpreter class comes with a wide variety of methods that can evaluate both java and python code and return or set the values in either java or python.

See jython-userguide as well as the PythonInterpreter javadoc

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