What is the difference between jython-standalone-2.7.0.jar and jython-2.7.0.jar

Question

I wrote a Java example, code:

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 successfully run java -jar target/jython-example-1.0-SNAPSHOT.jar , by the way, I used the maven-assembly-plugin to build the 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 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 

pyEngine seems to be null .

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

Answer 1

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

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

Working maven 2.7.1b2, which 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 website, it correctly includes the lib folder. This is just a version of the maven repository.

Answer 2

I believe that the main difference causing your problem 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 detailed description of the problem, as well as other issues and provides an alternative bank to get around some of the problems noted in the description.

I have no experience with scijava: jython-shaded, but I replaced it with your pom (for my setup, I also had to change jdk.version to 1.7 and JythonExample), and your example runs.