It looks simple and easy to understand. To achieve lazy import without breaking backward compatibility, I want to add one more rule: When package defines both of __getattr__ and __all__, automatic import of submodules are disabled (sorry, I don't have pointer to specification about this behavior). For example, some modules depends on email.parser or email.feedparser. But since email/__init__.py uses __all__, all submodules are imported eagerly. See https://github.com/python/cpython/blob/master/Lib/email/__init__.py#L7-L25 Changing __all__ will break backward compatibility. With __getattr__, this can be lazy import: import importlib def __getattr__(name): if name in __all__: return importlib.import_module("." + name, __name__) raise AttributeError(f"module {__name__!r} has no attribute {name!r}") Regards,