'Return ``True`` if `Range` header is present and if underlying
resource is considered unchanged when compared with `If-Range` header.'

def _is_range_request_processable(self, environ):

    return ((('HTTP_IF_RANGE' not in environ) or (not is_resource_modified(environ, self.headers.get('etag'), None, self.headers.get('last-modified'), ignore_if_range=False))) and ('HTTP_RANGE' in environ))
