Think Python - Denison University

192 Chapter 19. Casestudy: Tkinteroption: A value that controls the appearance orfunction ofawidget.keyword argument: An argument that indicates theparameter name aspart ofthe function call.callback: A function associated withawidget that iscalled when theuser performs anaction.bound method: A method associated withaparticular instance.event-driven programming: Astyleofprogramminginwhichtheflowofexecutionisdeterminedby user actions.event: A user action, likeamouse click orkey press,that causes aGUI torespond.event loop: Aninfinite loop that waits foruser actions and responds.item: A graphical element on aCanvas widget.bounding box: Arectanglethatenclosesasetofitems,usuallyspecifiedbytwoopposingcorners.pack: To arrange and displaythe elements ofaGUI.geometry manager: A system for packing widgets.binding: An association between a widget, an event, and an event handler. The event handler iscalled when theevent occurs inthe widget.19.11 ExercisesExercise 19.4 For this exercise, you willwritean image viewer. Here isasimpleexample:g = Gui()canvas = g.ca(width=300)photo = PhotoImage(file='danger.gif')canvas.image([0,0], image=photo)g.mainloop()PhotoImage reads a file and returns a PhotoImage object that Tkinter can display. Canvas.imageputs the image on the canvas, centered on the given coordinates. You can also put images on labels,buttons, and some other widgets:g.la(image=photo)g.bu(image=photo)PhotoImage can only handle a few image formats, like GIF and PPM, but we can use the PythonImaging Library (PIL)toread other files.The name of the PIL module is Image, but Tkinter defines an object with the same name. To avoidtheconflict, you can useimport...aslikethis:import Image as PILimport ImageTkThe first line imports Image and gives it the local name PIL. The second line imports ImageTk,which can translateaPILimage intoaTkinter PhotoImage. Here’san example: