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| = Programming Jython = [:../:FAQ Home] ---- '''Why can't I multiply inherit from two Java classes?''' In earlier versions of JPython, you actually could. This was deliberately disabled in 1.1 for a variety of good reasons. For a detailed discussion on this issue see the following archive messages: https://python.domainunion.de/pipermail/jpython-interest/1998-April/000213.html https://python.domainunion.de/pipermail/jpython-interest/1999-June/001874.html Note that you can still multiply inherit from any number of Python classes. ---- '''Why does dir(someJavaObject) return the empty list?''' Because the built-in dir() function returns a list of names called from the object's __dict__, __methods__, and __members__ attributes. In Python, an instance's methods live in the instance's class's dictionary, so dir(someJavaObject.__class__) would return a list of the method names (although only for the direct class, not for any base classes). ---- '''I'm trying to execute a 'protected' or 'private' Java Instance Method or attribute in a Java package. How can I get access?''' By default, as in Java, these methods are protected from external access, but there may be reasons, such as test scaffolding scripts, that this feature is not wanted. In the [jython home]/registry file: {{{ # Setting this to false will allow Jython to provide access to # non-public fields, methods, and constructors of Java objects. python.security.respectJavaAccessibility = false }}} ---- '''Can I reload a java class as is possible for python modules?''' The support for reloading java classes through reload(java-class), is disabled. The reload(java-class) only worked when the java class was a standalone class without any dependencies on other java classes (except the system class). When there was more than one class involved, the simple reload(java-class) no longer worked. Now on the other hand Jython 2.0 comes with some alternative (experimental) user-level support for java classes reloading ("jreload" module). See: https://www.jython.org/docs/jreload.html Further Jython 2.0 internal changes enable the expert user to play with reloading and class-loaders as he would from native java. ---- '''How can I access Java protected (static) members from a Jython subclass?''' The short answer: you can't. At least not without setting the registry option python.security.respectJavaAccessibility to false. It is difficult to add in a nice manner. The problem is a bit like this: A normal (public) static method is from jython called on the parent java class: javaclass.method() Such a call does not originate from the subclass, but from internal reflection code in jython. If we want to add support for calling protected static methods from a jython subclass, the call will have to originate from the subclass (ie. the proxy class), so we will have to generate a referring method in subclass proxy like: {{{#!java public static void method() { javaclass.method() } }}} (with the right return type and throws clauses) and the jython subclass will have to call the method on its own class, not the java class. ---- '''How can I use a Java null value in Jython?''' A java null is turned into a Python None value. {{{ import java >>> h = java.util.Hashtable() >>> print h.get("abc") None >>> if h.get("abc") is None: ... print "null returned" ... null returned >>> }}} ---- '''Where's the -O switch?''' Jython 2.0 does not have a -O command-line switch. Assigning __debug__=0 has been used to get -O behavior from things like "assert", but such assignments to __debug__ are considered an error, and in the future, will raise an exception. __debug__ is supposed to be a read-only variable. ---- ---- '''The Jython's os module is missing some functions, why?''' Python's and Jython's os modules differ necessarily because of differences Java imposes on natvie system access. For example, Java does not have a chdir equivalent, so it does not exist in Jython's os. There is an alternative os module that does provide additional functionality, and it is the jnios module found at: https://sourceforge.net/projects/jnios The jnios module replaces the default os module with a Java/JNI implementation of Python's os and posix modules. Jython CVS also has more functions in the os module (like system and the popen* functions). See ''The Jython's os module is missing some functions, why?'' below. ---- '''The Jython's os module is missing some functions, why?''' Use the os.system or os.popen* functions from Jython CVS. To use these functions, you'll need javaos.py, javashell.py, and popen2.py: https://cvs.sourceforge.net/cgi-bin/viewcvs.cgi/jython/jython/Lib/ You'll need to delete the 'from __future__ import division' line from javaos.py (this is a Python 2.2 feature not supported in Jython 2.1) Alternatively, you could use java.lang.Runtime.exec() directly, but the os functions handle a lot of complexity for you. --- |
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My name is Phoebe Rosenhain but everybody calls me Phoebe. I'm from Germany. I'm studying at the university (2nd year) and I play the Air horn for 6 years. Usually I choose songs from my famous films ;).
I have two brothers. I like Trainspotting, watching TV (Supernatural) and Sculling or Rowing.
Also visit my webpage - fat loss factor - fatlossfactorguides.com -