>> I should have to start that package somehow.
>
> `pip install` is a pretty good opt-in already imo

I think that’s where we disagree. Like others, I don’t want this to affect every python script in a given installation. 

>> Instead of just shipping "my_module.foo", you ship "my_module.py" and "_my_module.foo", where "my_module.py" looks like:
>
> but that's exactly my point, now you have to ship extra junk python files when it's a way better experience to have the hooks _just work_


You mean extra junk like .pth files? I don’t see the difference between a .py file and a .pth file, except I can’t opt out of .pth files. 

We’re just looking for some way to control the behavior, without giving the .pth file unlimited capabilities before the user script starts. If it’s “just” some extra .py files, then maybe that’s great. If we need some other new mechanism, then I’d be okay with that, too.