Overriding to make updating the defaults after instantiation of
        the option parser possible, _update_defaults() does the dirty work.

def get_default_values(self):
        """Overriding to make updating the defaults after instantiation of
        the option parser possible, _update_defaults() does the dirty work."""
        if not self.process_default_values:
            # Old, pre-Optik 1.5 behaviour.
            return optparse.Values(self.defaults)

        # Load the configuration, or error out in case of an error
        try:
            self.config.load()
        except ConfigurationError as err:
            self.exit(UNKNOWN_ERROR, str(err))

        defaults = self._update_defaults(self.defaults.copy())  # ours
        for option in self._get_all_options():
            default = defaults.get(option.dest)
            if isinstance(default, string_types):
                opt_str = option.get_opt_string()
                defaults[option.dest] = option.check_value(opt_str, default)
        return optparse.Values(defaults)