Tkinter callback problem

[Jeff Epler]

You could try using this definition of getint():
    def getint(x):
        if x == "??": return None
        return int(x)
that depends on the tk people being nice and never changing the "??"
string.  But if they'd make this incompatible change during a minor
release (hm, some python advocate should follow tcl/tk development and
raise hell when this happens) I wouldn't bet on it.

Jeff