'The conditional_etag keyword argument for Response will allow the
conditional match value of a If-Match request to be compared to a
non-standard value.
This is available for Storage Policies that do not store the client
object data verbatim on the storage nodes, but still need support
conditional requests.
It\'s most effectively used with X-Backend-Etag-Is-At which would
define the additional Metadata key(s) where the original ETag of the
clear-form client request data may be found.'

@property
def conditional_etag(self):

    if (self._conditional_etag is not None):
        return self._conditional_etag
    else:
        return self.etag
