Class definition example question

[Grant Edwards]

[background]

I'm working on a program to do design verification and
production test on a circuit board.  Most of the actual testing
is done by a C program with a whole boatload of obscure command
line options.  It works but it's not very friendly, so I'm
going to slap a GUI front-end on it.  I generally use STk for
stuff like this, but this time I decided to try Python since
most of the Linux machines around here come with Python and
Tkintr already installed, and I've got a better chance of
dumping maintenance duties on somebody else if it's not in
Scheme. ;)

[my example]

I've extended the Pmw "ScrolledText" class to add a "run"
method that runs a program in a sub-process and displays the
standard output in the contained text widget.  The class
definition is shown below.

My question is about the definition of the callback handler
"stdoutHandler".  If it's done this way, you end up with a
complete copy of the handler routine defined each time a
program is run.  I couldn't figure out any other way for the
callback routine to know what widget it belonged to.

It seems to work, but I'm pretty sure there's a more elegant
way to do this.

Would it be better to create a callback class with an instance
variable that points to associated widget?  Can an object
instance be passed to tkintr.createfilehandler?  Is this where
one needs to define a __call__ method?

Any helpful comments will be appreciated

#----------------------------------------------------------------------

class execWindow(Pmw.ScrolledText):

    def run(self,progPath):
    
        def stdoutHandler(file,mask,s=self):
        
            # read available data
            line = os.read(s.__fd,4096)
            
            # display it in window
            
            if line != "":
                s.insert('end',line)
            
            # done?
            
            r = s.__child.poll()
            
            if r != -1:
                Tkinter.tkinter.deletefilehandler(file)
                s.__returnCode = r
                s.insert('end', '[return=' + str(r) +']\n')
            
        self.__child = popen2.Popen3(progPath)
        self.__fd = self.__child.fromchild.fileno()
        
        fcntl.fcntl(self.__fd, FCNTL.F_SETFD, FCNTL.O_NDELAY);
        
        Tkinter.tkinter.createfilehandler(self.__child.fromchild,
                                  Tkinter.tkinter.READABLE,
                                  stdoutHandler)
                                  
#----------------------------------------------------------------------

-- 
Grant Edwards                   grante             Yow!  I guess we can live
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