How can I make silent exceptions louder in tkinter?

Question

If I run the following code from a terminal, I get a helpful error message in the terminal:

import Tkinter as tk  master = tk.Tk()  def callback():     raise UserWarning("Exception!")  b = tk.Button(master, text="This will raise an exception", command=callback) b.pack()  tk.mainloop() 

However, if I run it without a terminal (say, by double-clicking an icon), the error message is suppressed.

In my real, more complicated Tkinter application, I like that the GUI is a little crash-resistant. I don't like that my users have a hard time giving me useful feedback to fix the resulting unexpected behavior.

How should I handle this? Is there a standard way to expose tracebacks or stderror or whatnot in a Tkinter application? I'm looking for something more elegant than putting try/except everywhere.

EDIT: Jochen Ritzel gave an excellent answer below that pops up a warning box, and mentioned attaching it to a class. Just to make this explicit:

import Tkinter as tk import traceback, tkMessageBox  class App:     def __init__(self, master):         master.report_callback_exception = self.report_callback_exception         self.frame = tk.Frame(master)         self.frame.pack()         b = tk.Button(             self.frame, text="This will cause an exception",             command=self.cause_exception)         b.pack()      def cause_exception(self):         a = []         a.a = 0 #A traceback makes this easy to catch and fix      def report_callback_exception(self, *args):         err = traceback.format_exception(*args)         tkMessageBox.showerror('Exception', err)  root = tk.Tk() app = App(root) root.mainloop() 

My remaining confusion: Jochen mentions the possibility of having different exception reporting functions in different frames. I don't yet see how to do that. Is this obvious?

Answer 1

There is report_callback_exception to do this:

import traceback import tkMessageBox  # You would normally put that on the App class def show_error(self, *args):     err = traceback.format_exception(*args)     tkMessageBox.showerror('Exception',err) # but this works too tk.Tk.report_callback_exception = show_error 

If you didn't import Tkinter as tk, then do

Tkinter.Tk.report_callback_exception = show_error 

Answer 2

First a followup: Just today, a patch on the CPython tracker for the tkinter.Tk.report_callback_exception docstring made it clear that Jochen's solution is intended. The patch also (and primarily) stopped tk from crashing on callback exceptions when run under pythonw on Windows.

Second: here is a bare-bones beginning of a solution to making stderr function with no console (this should really be a separate SO question).

import sys, tkinter  root = tkinter.Tk()  class Stderr(tkinter.Toplevel):     def __init__(self):         self.txt = tkinter.Text(root)         self.txt.pack()     def write(self, s):         self.txt.insert('insert', s)  sys.stderr = Stderr()  1/0 # traceback appears in window 

More is needed to keep the popup window hidden until needed and then make it visible.