Question

If I have a button that executes a handler in relation to one toplevel window or root – can it modify a widget in another toplevel? What is the standard method of doing this?

Answer 1

I am not experienced in Tkinter, but I am sure its no different than PyQt4. Generally you want the parent child relationship. A parent widget contains children widgets and can modify them. The children should usually not know much about their parents and would communicate via signals or events.

When a handler fires, it should be free to modify the widgets it knows about. That is, if your top level window has 10 widgets, and contains the handler as a method, the method should be allowed to modify the 10 widgets through self attributes.

Something like:

class MyTopWindow:

    def __init__(self):
        self.widget1 = Widget
        self.widget2 = Widget
        self.button = Button

        #self.button.clicked -> self.handler   

    def handler(self):
        self.widget1.someAttribute = 1

button.click() # -> handler()

You make use of composition to build widgets inside of widgets. What you should avoid is a handler making some reference to a global widget that it really does not own.