为什么通用的“ try / except”块不适用于Python TkInter回调？

Question

I have determined that in a Python TkInter GUI program, it is best practice to enclose the entire thing in a try / except block in order to catch all exceptions and present them to the end user (as opposed to something going wrong silently or the program exiting for seemingly no reason).

However, this approach has some problems. Consider the following tiny program that attempts to divide by 0 when a button is clicked:

import tkinter

class Foo():
    def __init__(self):
        # Initialize a new GUI window
        root = tkinter.Tk()

        # The "Generic error" message is shown when the following is uncommented
        #number = 1 / 0

        # Define a button and draw it
        button = tkinter.Button(root, text='Generate an error', command=self.generate_error)
        button.pack()

        # Loop forever
        root.mainloop()

    def generate_error(self):
        # The "Generic error" message is not shown
        number = 1 / 0



if __name__ == '__main__':
    try:
        # Run the Foo class
        Foo()

    except Exception as e:
        print('Generic error:', str(e))

Why does the "Generic error" statement not apply to the button callback function?

Answer 1

The following StackOverflow post was helpful: Should I make silent exceptions louder in tkinter?

Basically, I need to use report_callback_exception . I've modified the code snippet accordingly:

import tkinter
import tkinter.messagebox
import traceback

class Foo():
    def __init__(self):
        # Initialize a new GUI window
        tkinter.Tk.report_callback_exception = callback_error  # TkInter callbacks run in different threads, so if we want to handle generic exceptions caused in a TkInter callback, we must define a specific custom exception handler for that
        root = tkinter.Tk()

        # The error() function is triggered when the following is uncommented
        #number = 1 / 0

        # Define a button and draw it
        button = tkinter.Button(root, text='Generate an error', command=self.generate_error)
        button.pack()

        # Loop forever
        root.mainloop()

    def generate_error(self):
        # The "callback_error()" function is triggered when the button is clicked
        number = 1 / 0


def error(message, exception):
    # Build the error message
    if exception is not None:
        message += '\n\n'
        message += traceback.format_exc()

    # Also log the error to a file
    # TODO

    # Show the error to the user
    tkinter.messagebox.showerror('Error', message)

    # Exit the program immediately
    exit()


def callback_error(self, *args):
    # Build the error message
    message = 'Generic error:\n\n'
    message += traceback.format_exc()

    # Also log the error to a file
    # TODO

    # Show the error to the user
    tkinter.messagebox.showerror('Error', message)

    # Exit the program immediately
    exit()



if __name__ == '__main__':
    try:
        # Run the Foo class
        Foo()

    except Exception as e:
        error('Generic error:', e)