Readline eats exceptions raised by completer functions.

def complete_wrap(self, func, *args, **kwargs):
        """ Readline eats exceptions raised by completer functions. """
        # Workaround readline's one-time-read of terminal width.
        termcols = shutil.get_terminal_size()[0]
        readline.parse_and_bind('set completion-display-width %d' % termcols)
        try:
            return func(*args, **kwargs)
        except:
            traceback.print_exc()
            raise