What's the difference between jython-standalone-2.7.0.jar and jython-2.7.0.jar

Question

I wrote a Java example, the code is:

import org.python.core.PyObject;
import org.python.util.PythonInterpreter;

import javax.script.ScriptEngine;
import javax.script.ScriptEngineFactory;
import javax.script.ScriptEngineManager;
import javax.script.ScriptException;
import java.util.List;

class JythonExample {

  public static void main(String args[]) throws ScriptException {
    listEngines();

    ScriptEngineManager mgr = new ScriptEngineManager();
    ScriptEngine pyEngine = mgr.getEngineByName("python");

    try {
      pyEngine.eval("print \"Python - Hello, world!\"");
    } catch (Exception ex) {
      ex.printStackTrace();
    }

    final PythonInterpreter interpreter = new PythonInterpreter();
    interpreter.exec("print \"Python - Hello, world!\"");

    PyObject result = interpreter.eval("2 + 3");
    System.out.println(result.toString());
  }

  public static void listEngines(){
    ScriptEngineManager mgr = new ScriptEngineManager();
    List<ScriptEngineFactory> factories =
        mgr.getEngineFactories();
    for (ScriptEngineFactory factory: factories) {
      System.out.println("ScriptEngineFactory Info");
      String engName = factory.getEngineName();
      String engVersion = factory.getEngineVersion();
      String langName = factory.getLanguageName();
      String langVersion = factory.getLanguageVersion();
      System.out.printf("\tScript Engine: %s (%s)\n",
          engName, engVersion);
      List<String> engNames = factory.getNames();
      for(String name: engNames) {
        System.out.printf("\tEngine Alias: %s\n", name);
      }
      System.out.printf("\tLanguage: %s (%s)\n",
          langName, langVersion);
    }
  }
}

In my pom.xml, if I use:

<dependency>
    <groupId>org.python</groupId>
    <artifactId>jython-standalone</artifactId>
    <version>2.7.0</version>
</dependency>

then I can run java -jar target/jython-example-1.0-SNAPSHOT.jar successfuly, by the way, I used maven-assembly-plugin to build a runnable jar.

if I use:

<dependency>
    <groupId>org.python</groupId>
    <artifactId>jython</artifactId>
    <version>2.7.0</version>
</dependency>

then when I run java -jar target/jython-example-1.0-SNAPSHOT.jar, I'll always get the following error:

ScriptEngineFactory Info
    Script Engine: jython (2.7.0)
    Engine Alias: python
    Engine Alias: jython
    Language: python (2.7)
ScriptEngineFactory Info
    Script Engine: Oracle Nashorn (1.8.0_31)
    Engine Alias: nashorn
    Engine Alias: Nashorn
    Engine Alias: js
    Engine Alias: JS
    Engine Alias: JavaScript
    Engine Alias: javascript
    Engine Alias: ECMAScript
    Engine Alias: ecmascript
    Language: ECMAScript (ECMA - 262 Edition 5.1)
java.lang.NullPointerException
    at me.soulmachine.JythonExample.main(JythonExample.java:21)
Exception in thread "main" ImportError: Cannot import site module and its dependencies: No module named site
Determine if the following attributes are correct:
  * sys.path: ['/home/programmer/src/github/JythonExample/JythonExample/target/Lib', '__classpath__', '__pyclasspath__/']
    This attribute might be including the wrong directories, such as from CPython
  * sys.prefix: /home/programmer/src/github/JythonExample/JythonExample/target
    This attribute is set by the system property python.home, although it can
    be often automatically determined by the location of the Jython jar file

You can use the -S option or python.import.site=false to not import the site module

It seems the pyEngine is null.

So I wonder what's the difference between jython-standalone-2.7.0.jar and jython-2.7.0.jar

Answer 1

One problem I've just discovered with the same error is that the maven build 2.7.0 does not include the lib folder. This is probably a build error for the release build. I had to move up the b2 build which does properly include the lib folder in the supplied jar.

Problem maven 2.7.0 jar:
<dependency> <groupId>org.python</groupId> <artifactId>jython-standalone</artifactId> <version>2.7.0</version> </dependency>

Working maven 2.7.1b2 that includes the lib folder:
<dependency> <groupId>org.python</groupId> <artifactId>jython-standalone</artifactId> <version>2.7.1b2</version> </dependency>

NOTE: If you download the jar directly from the Jython site it does correctly include the lib folder. It's just the maven repository version.

Answer 2

I believe the main difference causing your issue is that the jython-standalone jar provides Lib/ (which contains site.py) while the jython jar does not.

https://github.com/scijava/jython-shaded gives a more in-depth description of the issue, as well as other issues, and provides an alternative jar to get around some issues noted in the description.

I don't have experience with scijava:jython-shaded, but I substituted it into your pom (for my setup I also had to change jdk.version to 1.7 and to JythonExample) and your example runs.