An attribute of the current server's description.

        If the client is not connected, this will block until a connection is
        established or raise ServerSelectionTimeoutError if no server is
        available.

        Not threadsafe if used multiple times in a single method, since
        the server may change. In such cases, store a local reference to a
        ServerDescription first, then use its properties.

def _server_property(self, attr_name):
        """An attribute of the current server's description.

        If the client is not connected, this will block until a connection is
        established or raise ServerSelectionTimeoutError if no server is
        available.

        Not threadsafe if used multiple times in a single method, since
        the server may change. In such cases, store a local reference to a
        ServerDescription first, then use its properties.
        """
        server = self._topology.select_server(
            writable_server_selector)

        return getattr(server.description, attr_name)