'Filter the current expression.'

def Filter(self, match=None, **_):

    arg = self.stack.pop((-1))
    for filter_name in match.group(1).split(','):
        filter_object = ConfigFilter.classes_by_name.get(filter_name)
        if (filter_object is None):
            raise FilterError(('Unknown    filter    function    %r' % filter_name))
        logging.debug('Applying    filter    %s    for    %s.', filter_name, arg)
        arg = filter_object().Filter(arg)
    self.stack[(-1)] += arg
