Tkinter and exceptions

[Peter Otten]

Nick Craig-Wood wrote:

> I'm just starting out with Tkinter programming (using Programming
> Python as a reference), and I couldn't find the answer to this
> anywhere...
> 
> How do you catch general exceptions in a Tkinter program.  If you run
> the below and click the "Exception" or "Callback Exception" buttons
> you see a traceback on stderr under unix, and nothing at all under
> windows (if run as a pyw).
> 
> How so you catch those exceptions so that they can pop up in a dialog?
> There doesn't seem to be a hook. I was imagining that there would be a
> global error handler I could hook / override?

Overriding report_callback_exception() seems to work:

 
> from Tkinter import *
  
  import traceback
  import tkMessageBox

> 
> class AppDemo(Frame):
>     """A sample tk app"""
> 
>     def __init__(self, parent=None):
>         Frame.__init__(self, parent)
>         self.pack(expand=YES, fill=BOTH)
>         self.make_tool_bar()
>         self.master.title("A Title")
>         self.bang = 0

        def show_error(*args):
            a = traceback.format_exception(*args)
            tkMessageBox.showerror(a[-1], "\n".join(a[:-1]))
        self._root().report_callback_exception = show_error

>         self.process()
> 
>     def process(self):
>         self.after(1000, self.process)
>         if self.bang:
>             self.bang = 0
>             raise ValueError("Callback Exception")
>         
>     def make_tool_bar(self):
>         self.toolbar = Frame(self, cursor='hand2', relief=SUNKEN, bd=2)
>         self.toolbar.pack(side=BOTTOM, fill=X)
>         Button(self.toolbar, text='Exception',
>         command=self.make_exception).pack(side=TOP, fill=X)
>         Button(self.toolbar, text='Callback Exception',
>         command=self.make_callback_exception).pack(side=TOP, fill=X)
>         Button(self.toolbar, text='Quit',
>         command=self.quit).pack(side=TOP, fill=X)
> 
>     def make_exception(self):
>         raise ValueError("Exception")
> 
>     def make_callback_exception(self):
>         self.bang = 1
> 
> if __name__ == "__main__":
>     AppDemo().mainloop()

Peter