Hi John and Alan, I got it! Thank you both for explaining this situation.
Thanks, Joe ________________________________________________ Get your own "800" number Voicemail, fax, email, and a lot more http://www.ureach.com/reg/tag ---- On Tue, 22 Nov 2005, [EMAIL PROTECTED] ([EMAIL PROTECTED]) wrote: > >>I'm puzzled by the 'command' option in menu and Button of > >>Tkinter. With the following lines, > > The command value needs to be a *reference* to a function. > > That is not the function call itself but a reference to the function > that will be \called. > > Let me illustrate the difference: > > def f(): print 'Its me!' > > f() # prints the message > > g = f # this assigns a reference to f > > g() # this now calls that reference, > so calling g() is the same as calling f() > > > >>menu.add_command(label="Open Viewer", > command=os.system("Open my viewer &")) > > Here you assign the result of the os.system() > call to command, in fact you want to assign > a reference to a call of os.system which will > be executed when the menu/button is activated. > > The more straightforward way to do that is to > define a short function that calls os.system: > > def callSystem(): > os.system(Mycommand) > > And make the menu/button reference callSystem: > > >>menu.add_command(label="Open Viewer", > command=callSystem) > > Notice no parens, just the name of the function. > > Because we can wind up with loads of these little > wrapper functions there is a shortcut called lambda. > With lambda we can avoid defining a new mini function: > > >>menu.add_command(label="Open Viewer", > command=lambda : os.system("Open my viewer &")) > > the thing that follows the lambda is what gets > executed when the widget activates. > > Does that help? > > Alan G. > http://www.freenetpages.co.uk/hp/alan.gauld _______________________________________________ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
