You can add some bolt-on features to speed some things up, but it is much nicer when things are fast by default, by design. Instead you could have the opposite

You can add some bolt-on features to speed some things up, but it is much nicer when things are fast by default, by design. Instead you could have the opposite kind of annotations, e.g., decorators for classes @monkeypatchable or @attributes_can_be_added_outside_of_init; after all, those features are rarely needed, and it's good to optimize for the common case.