Exception hooks

In wxPython, it's possible to handle uncaught exceptions with an exception hook. Wax makes this especially easy: in a given frame, define or override the __ExceptHook__ method. (Usually you'll want to use the root frame for this.)

The __ExceptHook__ method must be defined with three parameters (besides self):

class MyFrame(Frame):
    def __ExceptHook__(self, exctype, value, traceback):
        ...handle exception...

• exctype is the class of the exception that was raised.
• value is the value that was passed to the exception (usually a string describing what went wrong).
• traceback is a traceback object that can be printed, inspected, etc. (For more information about what is possible with these objects, see the traceback module in the Python standard library.)

If the root frame has an __ExceptHook__ method, then it will be assigned to sys.excepthook when the application is initialized. If you use other code or libraries that set sys.excepthook as well, this may cause a conflict.

Using __ExceptHook__ to write a simple handler

The following example demonstrates how to use this method.

# excepthook-1.py

from wax import *

class MainFrame(Frame):
    def Body(self):
        b = Button(self, "Generate exception", event=self.OnButtonClick)
        self.AddComponent(b, expand='both', border=5)
        self.Pack()
        self.Size = 100, 100
    def OnButtonClick(self, event):
        print 1/0
    def __ExceptHook__(self, exctype, value, traceback):
        print "The following exception was caught:"
        print "exctype:", exctype
        print "value:", value
        print "traceback:", traceback

app = Application(MainFrame)
app.Run()

When the button is clicked, it produces output similar to the following:

The following exception was caught:
exctype: exceptions.ZeroDivisionError
value: integer division or modulo by zero
traceback: <traceback object at 0x0191A3A0>

Writing a more user-friendly handler using ErrorDialog

The ErrorDialog widget (defined in tools/errordialog.py) was designed to cooperate with __ExceptHook__ and handle uncaught exceptions gracefully. Here's how to use it:

# excepthook-2.py

from wax import *
from wax.tools.errordialog import ErrorDialog

class MainFrame(Frame):
    def Body(self):
        b = Button(self, "Generate exception", event=self.OnButtonClick)
        self.AddComponent(b, expand='both', border=5)
        self.Pack()
        self.Size = 100, 100
    def OnButtonClick(self, event):
        print 1/0
    def __ExceptHook__(self, exctype, value, traceback):
        dlg = ErrorDialog(self, exctype, value, traceback)
        dlg.ShowModal()
        dlg.Destroy()

app = Application(MainFrame)
app.Run()

Clicking the button will generate an exception, which will cause the handler to produce this dialog: