Getting Started

Nate Jensen edited this page Jul 12, 2018 · 16 revisions

Since Jep 3.0


Jep requires that the following dependencies be installed before it can be built and run:

  • JDK >= 1.7
  • Python = 2.7, 3.3, 3.4, 3.5, or 3.6, 3.7

Building Jep

If you cloned or downloaded the Jep source, you will need to build Jep. Simply run

python build

If the build succeeds it will create a directory jep/build which will contain a jep.jar and the compiled C library of Jep, typically named or jep.dll depending on your platform.

Installing Jep

There are multiple ways to install Jep, in order of least involved to most involved:

  1. If you used pip install jep, Jep should already be built and installed.
  2. If you built the source yourself, you can run python install to install Jep to the standard dirs.
  3. If you would like to include jep as part of your application, you can place the files as necessary presuming the following conditions are met:
  • The jep.jar is accessible to the Java classloaders (typically through the Java classpath)
  • The shared library ( or jep.dll) is accessible by the Java process (typically through -Djava.library.path or the environment variable LD_LIBRARY_PATH)
  • The jep python files (,,, etc) are accessible by Python (typically by placing them in the site-packages/jep directory).

Example Code

Using Jep in your application is designed to be easy to intermix Java and Python objects in the Python interpreter.

Hello World

try(Jep jep = new Jep()) {
    jep.eval("from java.lang import System");
    jep.eval("s = 'Hello World'");

Calling Python methods from Java and getting results

try(Jep jep = new Jep()) {
    jep.eval("import somePyModule");
    // any of the following work, these are just pseudo-examples

    // using eval(String) to invoke methods
    jep.set("arg", obj);
    jep.eval("x = somePyModule.foo1(arg)");
    Object result1 = jep.getValue("x");

    // using getValue(String) to invoke methods
    Object result2 = jep.getValue("somePyModule.foo2()");

    // using invoke to invoke methods
    jep.eval("foo3 = somePyModule.foo3")
    Object result3 = jep.invoke("foo3", obj);

   // using runScript

Calling Java constructors from Python

# importing the java.lang.Class objects
from java.util import HashMap
from java.util import ArrayList as AL

# instantiation
x = HashMap()
y = HashMap(100)
a = AL()

Calling Java methods from Python

from java.util import ArrayList, HashMap

a = ArrayList()
a += "def"

m = HashMap()
m.put("listkey", a)
m["otherkey"] = "xyz"
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