How to check the classpath where Jython ScriptEngine looks for python module?

Question

I have this Java code which I am using to run a python script using Jython ScriptEngine:

StringWriter writer = new StringWriter();
ScriptEngineManager manager = new ScriptEngineManager();
ScriptContext context = new SimpleScriptContext();

context.setWriter(writer);
ScriptEngine engine = manager.getEngineByName("python");
engine.eval(new FileReader("/Users/folder1/test.py"), context);

In my python script there are several module import statements and when I run the Java code I get error as javax.script.ScriptException: ImportError: No module named psycopg2. All the modules are installed in my machine and when I run the python script normally through CLI it executes. So my understanding is that Jython classpath is looking somewhere else for the python modules.

How can I check where does the Jython ScriptEngine looks for modules and then modify it include where actually my python modules are present? I am new to this so please forgive any lack of understanding.

Note: I have CentOS and python 2.7.5 installed on my machine

Answer 1

sys.path is a list of strings that specifies where Jython (and Python) searches for modules. You can check its value like so:

engine.eval("import sys; print sys.path");

To add a directory to sys.path, use the JYTHONPATH environment variable. If yourmodule is installed in /path/to/modules/yourmodule, it would look like this:

export JYTHONPATH=/path/to/modules

Another way is to use the python.path property.

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Unfortunately, in the case of psycopg2 the above won't help since that package is a C extension and therefore only compatible with CPython. Perhaps you can use the port of Psycopg for Ctypes instead.

Answer 2

An alternative way to add path to folder with custom python libs using ScriptEngine:

engine.eval("import sys; sys.path.append(\"/some/path/to/folder/withpylibs\")");