other thingsthe classes arrange for automatic quit verification dialog pop ups and icon file searching for instancethe window classes always search the current working directory and the directory containing this module for window icon fileonce per process by using classes that encapsulate--that ishide--such detailswe inherit powerful tools without having to think about their implementation again in the future moreoverby using such classeswe'll give our applications standard look-and-feel and behavior and if we ever need to change that appearance or behaviorwe have to change code in only one placenot in every window we implement to test this utility moduleexample - exercises its classes in variety of modes-as mix-in classesas superclassesand as calls from nonclass code example - pp \gui\tools\windows-test py must import windows to testelse __name__ is __main__ in findicon from tkinter import buttonmainloop from windows import mainwindowpopupwindowcomponentwindow def _selftest()mixin usage class content"same code used as tktopleveland framedef __init__(self)button(selftext='larch'command=self quitpack(button(selftext='sing 'command=self destroypack(class contentmix(mainwindowcontent)def __init__(self)mainwindow __init__(self'mixin''main'content __init__(selfcontentmix(class contentmix(popupwindowcontent)def __init__(self)popupwindow __init__(self'mixin''popup'content __init__(selfprev contentmix(class contentmix(componentwindowcontent)def __init__(self)componentwindow __init__(selfprevcontent __init__(selfcontentmix(nested frame on prior window sing erases frame subclass usage class contentsub(popupwindow)def __init__(self)popupwindow __init__(self'popup''subclass'wrapping up top-level window interfaces