code: def response(code, body='', etag=None, last_modified=None, expires=None, **kw):
      if etag is not None:
          if not (etag[0] == '"' and etag[-1] == '"'):
              etag = '"%s"' % etag
          kw['etag'] = etag
      if last_modified is not None:
          kw['last_modified'] = datetime_to_httpdate(last_modified)
      if expires is not None:
          if isinstance(expires, datetime):
              kw['expires'] = datetime_to_httpdate(expires)
          else:
              kw['expires'] = timedelta_to_httpdate(expires)
      headers = [(k.replace('_', '-').title(), v) for k, v in sorted(kw.items())]
      return Response(code, headers, body)