Software Design Lecture Notes
Fall 2004


Tips on Chatters and Rooms
--------------------------

One way to make up a name for your Chatter:

        from random import randrange
        self.login = os.getlogin()
        self.name = 'chatter_%s%d' % (self.login, randrange(1000))


In working on your Chatter and Room implementations, you
might find it tricky to handle KeyboardInterrupts correctly.
As an example, here is the version of stoppableLoop from
RemoteObject.py

    def stoppableLoop(self):
        # run handleRequests until another thread clears self.running
        self.running = 1
        while self.running:
            self.demon.handleRequests(0.1)
        self.cleanup()

If this ends normally, it cleans up after itself, but if the user
presses Control-C while the thread is running the loop, it might
exit without cleaning up.  One way to fix that is with the finally
clause:

    def stoppableLoop(self):
        # run handleRequests until another thread clears self.running
        self.running = 1
        try:
            while self.running:
                self.demon.handleRequests(0.1)
        finally:
            self.cleanup()

The finally clause always executes, whether an exception occurs
or not.  For more details, I recommend "Python in a Nutshell".

An alternative is to use an except clause, as I did in my
implementation of Chatter:

    try:
        chat.mainloop()
    except:
        chat.quit()
        (type, value, traceback) = sys.exc_info()
        if type != KeyboardInterrupt:
            raise type, value

If an exception occurs while mainloop is running, we execute
quit (which executes cleanup).  If the exception is anything
other than a KeyboardInterrupt, we "propagate" the exception
by re-raising it.

See if you prove, by inspection of your code, that the program cannot
exit (either normally or with an exception) without cleaning up!


Scrollable text
---------------

I've added a couple of widgets to World.py

You have to download the newest version to get them.
Here's the new code

    # scrollbar
    def sb(self, side=TOP, fill=NONE, expand=0, anchor=CENTER, **options):
        return self.widget(Scrollbar, side, fill, expand, anchor, **options)

    class ScrollableText:
        def __init__(self, gui,
                     side=TOP, fill=NONE, expand=0, anchor=CENTER, **options):
            self.frame = gui.fr(side, fill, expand, anchor, **options)
            self.scrollbar = gui.sb(RIGHT, fill=Y)
            self.text = gui.te(LEFT, wrap=WORD,
                                 yscrollcommand=self.scrollbar.set)
            self.scrollbar.config(command=self.text.yview)
            gui.endfr()
            
    # scrollable text
    # returns a ScrollableText object that contains a frame, a
    # text entry and a scrollbar.
    # note: the options provided to st apply to the frame only;
    # if you want to configure the other widgets, you have to do
    # it after invoking st
    def st(self, side=TOP, fill=NONE, expand=0, anchor=CENTER, **options):
        return self.ScrollableText(self, side, fill, expand, anchor, **options)

Here's how you can create a ScrollableText widget:

    st = self.st()

And here's how you can add text to it:

    st.text.insert(END, message + '\n')