How to use eval via Jython?

Question

I am trying to use the original eval in Python, via Jython. But for some reason I don't understand, I am getting a NullPointerExec.

public static String Parse(String s)
{
    ScriptEngine engine = new ScriptEngineManager().getEngineByName("python");
    try 
    {
        return engine.eval("eval('%s')".format(s)).toString();
    } 
    catch (ScriptException e) 
    {
        e.printStackTrace();
    }

    return "--";
}

Answer 1

You can use Pythons eval function through Java (and Jython) like this:

public static boolean XLargerThanY(int x, int y) throws ScriptException {
  PyScriptEngineFactory factory = new PyScriptEngineFactory();
  ScriptEngine engine = factory.getScriptEngine();
  PyFunction function = (PyFunction) engine.eval("x > y");
  PyBoolean ans = (PyBoolean) function.__call__(new PyInteger(x), new PyInteger(y));
  return ans.getBooleanValue();
}