cleanup actions on sys.exit()

[Jindra]

Hello,
I wrote a GUI app in Jython (using Java Swing) which uses database. The application remains connected for its whole run time until the main window is closed (JFrame, using defaultCloseOpe ration = JFrame.EXIT_ON_ CLOSE).
Now, when exiting, I would like to make sure I explicitly close the database connection. Is there any function, like _atexit() in C, where I could place my code?
Thank you very much.

[dwblas]

I use the __del__ function however because of the way the Python garbage collector uses a count of references, you may have to be explicit on closing some objects, like file pointers.

http://eli.thegreenplace.net/2009/06/12/safely-using-destructors-in-python/

[Jindra]

Oh, yes, this is what I was looking for but could not find! :) Thank you, dwblas!
Strangely, I haven't heard of __del__ since I first learn some python (version 1.6, I guess).
In the meantime, I found there is one more way in Swing, and that is Runtime.addShut downHook(Thread ).
I defined this function:

class ShutdownTask( java.lang.Thread ):
    def __init__( self, connection ):
        self.conn = connection
        print 'ShutdownTask setup: object = %s' % connection
    def run( self ):
        print 'ShutdownTask in progress'
        if self.conn is not None:
            try:
                print 'ShutdownTask: shutting down database connection'
                self.conn.conn.close()
                print 'ShutdownTask: connection closed'
            except Exception, e:
                print 'ShutdownTask: exception'
                print e
        print 'ShutdownTask: done'

and in the init thread I call this:

    Q = Connection() # my class to represent database connection
    shutdownTask = ShutdownTask( Q )
    java.lang.Runtime.getRuntime().addShutdownHook( shutdownTask )

Works perfectly and is "Swing native", but __del__ in the main GUI class should do the same job.