Working with message boxes

Now, let's complete the code for the About and Help menus. The functionality is simple. When a user clicks on the Help or About menu, a message window pops up and waits for the user to respond by clicking on a button. Though we can easily code new Toplevel windows to show the About and Help messages, we will instead use a module called messagebox to achieve this functionality.

The messagebox module provides ready-made message boxes to display a wide variety of messages in applications. The functions available through this module include showinfo, showwarning, showerror, askquestion, askokcancel, askyesno, askyesnocancel, and askretrycancel, as shown in the following screenshot:

To use this module, we simply import it into the current namespace by using the following command:

import tkinter.messagebox 

A demonstration of the commonly used functions of messagebox is provided in 2.08.py in the code bundle. The following are some common usage patterns:

 import tkinter.messagebox as tmb
 tmb.showinfo(title="Show Info", message="This is FYI")
 tmb.showwarning(title="Show Warning", message="Don't be silly")
 tmb.showerror(title="Show Error", message="It leaked")
 tmb.askquestion(title="Ask Question", message="Can you read this?")
 tmb.askokcancel(title="Ask OK Cancel", message="Say Ok or Cancel?")
 tmb.askyesno(title="Ask Yes-No", message="Say yes or no?")
 tmb.askyesnocancel(title="Yes-No-Cancel", message="Say yes no cancel")
 tmb.askretrycancel(title="Ask Retry Cancel", message="Retry or what?")

Equipped with an understanding of the messagebox module, let's code the about and help functions for the code editor. The functionality is simple. When a user clicks on the About or Help menu item, a showinfomessagebox pops up.

To achieve this, include the following code in the editor (2.09.py):

def display_about_messagebox(event=None):
     tkinter.messagebox.showinfo("About", "{}{}".format(PROGRAM_NAME,                     
       "\nTkinter GUI Application\n Development Blueprints"))
 

def display_help_messagebox(event=None):
     tkinter.messagebox.showinfo("Help", "Help Book: \nTkinter GUI                           
       Application\n Development Blueprints", icon='question')

Then, attach these functions to the respective menu items, as follows:

about_menu.add_command(label='About', command=display_about_messagebox)
about_menu.add_command(label='Help', command=display_help_messagebox)

Next, we will add the quit confirmation feature. Ideally, we should have implemented file saving in the event the text content has been modified, but for the sake of simplicity I am not putting in that logic here and instead am displaying a prompt for the user to determine whether the program should be closed or kept open. Accordingly, when the user clicks on File | Exit, it prompts an Ok-Cancel dialog to confirm the quit action:

def exit_editor(event=None):
       if tkinter.messagebox.askokcancel("Quit?", "Really quit?"):
            root.destroy() 

Then, we override the Close button and redirect it to the exit_editor function that we previously defined, as follows:

root.protocol('WM_DELETE_WINDOW', exit_editor)

Then, we add a callback command for all the individual menu items, as follows:

file_menu.add_command(label='Exit', accelerator='Alt+F4', command= exit_editor)
about_menu.add_command(label='About', command = display_about_messagebox)
about_menu.add_command(label='Help', command = display_help_messagebox)

Finally, add the bindings for the keyboard shortcut to display help: 

content_text.bind('<KeyPress-F1>', display_help_messagebox) 

This completes the iteration.