Identical callback problems

[sragsdale at my-deja.com]

I've got a GUI that is trying to execute the same callback from two
different events.  One is working and the other isn't, even though it's
the same callback.

Basically, it's a program that opens a modal dialog box so that the user
can enter information.  When the callback is bound to a button, the
dialog box opens without problems.  When the callback is bound to a
double-click, the dialog box STILL opens but I get an error saying
"TclError: grab failed: window not viewable".  It's not an invocation
problem since the creation of a DlogBox isn't dependent on anything.
Any idea how I can satisfy tk so that it doesn't complain about this?

To see the bug, run the program below.  Double-click on the left side
(error) and then click the button on the right (no error).

=================================================================
from Tkinter import *

# this just pops up a modal dialog box with a button in it
class DlogBox(Toplevel):
    def __init__(self):
        Toplevel.__init__(self)
        f1 = Frame(self)
        f1.pack(anchor=N, expand=YES, fill=X)
        Button(self, text='OK', command=self.destroy).pack(anchor=S)
        self.grab_set()         # make myself modal:
        self.focus_set()        # mouse grab, keyboard focus, wait...
        self.wait_window()      # till destroy; else returns to caller
now

# The main app
class TestApp(Frame):
    def __init__(self,parent=None):
        Frame.__init__(self,parent,relief=GROOVE,borderwidth=4)
        self.pack(expand=YES, fill=BOTH)
        items = Listbox(self)
        items.pack(side=LEFT, expand=YES, fill=BOTH)

        # bind the button to the callback
        button = Button(self,text="Foo",command=self.callback)
        button.pack(side=RIGHT,expand=YES, fill=BOTH)

        # bind a double-click on the Listbox to the callback
        items.bind('<Double-1>', self.callback)

    # the callback that exposes the DlogBox
    def callback(self,event=None):
        print "Callback called with",event
        DlogBox()

if __name__ == '__main__':
    TestApp().mainloop()


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