Message12210

I don't think this is the Java 9 / Jigsaw problem. The message is not the same.

This will cause trouble:

                interpreter.exec("sys.path.append(\"/Library/Python/2.7/site-packages\")");

because CPython and Jython just don't mix. And if I count correctly, this is the place the stack dump ends. I'm stumped, though. How can there be any problem with access to PyList.getList() from PyShadowString in the same package, via the same classloader (from the same JAR)?

I believe you need a full installation of Jython and then use the pip it gives you to install the packages you need (which have to be pure Python) in the site-packages of your Jython library.