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Embed Python in Java
C Java Python Other
branch: master


Jep - Java Embedded Python

Jep embeds CPython in Java. It is safe to use in a heavily threaded environment, it is quite fast and its stability is a main feature and goal.

Some benefits of CPython over Java-based languages:

  • Using the native Python interpreter may be much faster.
  • Python is mature and well supported, so there's no fear the interpreter will suddenly change widely-used features.
  • Access to the high quality Python modules, both native and Python-based.
  • Compilers and assorted Python tools are as mature as the language.
  • Python is an ideal language for your business logic. It is easy to learn, readable and generally immune to programming gotchas.

Patches, comments and other help is greatly appreciated. If you need help, post to the SourceForge mailing list or forums. Please include code snippets for the most accurate response.

Jep is licensed zlib/libpng license to avoid linking issues.


Simply run pip install jep.


  • Python version >= 2.6
  • JNI >= 1.4

Building on Mac OS X

OS X requires the Java Developer Package and Xcode from Apple. They are free to download.


You'll need to use the same compiler that your Python is built with. That's usually MSVC.

Note that Oracle is now building Java with a MSVCRT version that is not easily linked with using tools that I have. Using native modules on Windows has not worked in recent years because the compilers are not widely available. If an OpenJDK build used MinGW, that'd be much more likely to work.

Running scripts

The script will provide a jep shortcut to make launching Java and Python easier.

$ jep
>>> from java.lang import System
>>> System.out.println('hello, world')
hello, world

Running on *nix

Due to some (common) difficulties with Java and C projects that dlopen libraries, you may need to set LD_PRELOAD environment variable. That's in addition to setting LD_LIBRARY_PATH if you've installed libjep into a directory not cached by

See the contents of the installed jep script for an example how to do this. The script should have the correct values for your interpreter and virtualenv (if present).

Running the tests

The tests are run from

$ python test


For issues and source control, use github:

There's also a Sourceforge mailing list that is the best way to get support for Jep:

Mike Johnson

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