问Python:用于os.system()和os.popen()的NullPointerException

EN

import sys
import os

print (sys.version)   #This line works on both servers and gives 2.2.1 os output 
os.system('pwd')
os.popen('hostname -f').read().rstrip('\n')

*File "/u01/oracle/mwhome/wlserver_10.3/common/wlst/modules/jython-modules.jar/Lib/javaos$py.class", line 333, in system
File "/u01/oracle/mwhome/wlserver_10.3/common/wlst/modules/jython-modules.jar/Lib/popen2.py", line 31, in ?
File "/u01/oracle/mwhome/wlserver_10.3/common/wlst/modules/jython-modules.jar/Lib/javashell.py", line 17, in ?
File "/u01/oracle/mwhome/wlserver_10.3/common/wlst/modules/jython-modules.jar/Lib/string$py.class", line 434, in ?
    at java.io.File.<init>(File.java:222)
    at java.lang.Package$1.run(Package.java:527)
    at java.lang.Package.defineSystemPackage(Package.java:520)
    at java.lang.Package.getSystemPackages(Package.java:511)
    at java.lang.ClassLoader.getPackages(ClassLoader.java:1513)
    at java.lang.ClassLoader.getPackages(ClassLoader.java:1511)
    at java.lang.Package.getPackages(Package.java:281)
    at org.python.core.JavaImportHelper.buildLoadedPackages(Unknown Source)
    at org.python.core.JavaImportHelper.tryAddPackage(Unknown Source)
    at org.python.core.imp.import_next(Unknown Source)
    at org.python.core.imp.import_name(Unknown Source)
    at org.python.core.imp.importName(Unknown Source)
    at org.python.core.ImportFunction.load(Unknown Source)
    at org.python.core.ImportFunction.__call__(Unknown Source)
    at org.python.core.PyObject.__call__(Unknown Source)
    at org.python.core.__builtin__.__import__(Unknown Source)
    at org.python.core.imp.importFromAs(Unknown Source)
    at org.python.core.imp.importFrom(Unknown Source)
    at string$py.f$0(C:\wlst\jython_2.2.1\Lib\string.py:434)
    at string$py.call_function(C:\wlst\jython_2.2.1\Lib\string.py)
    at org.python.core.PyTableCode.call(Unknown Source)
    at org.python.core.PyCode.call(Unknown Source)
    at org.python.core.imp.createFromCode(Unknown Source)
    at org.python.core.imp.createFromPyClass(Unknown Source)
    at org.python.core.ZipFileImporter$ZipFileLoader.load_module(Unknown Source)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
java.lang.NullPointerException: java.lang.NullPointerException*