It's a _NamespacePath in 3.7 because there's no __init__.py in the top-level "google" directory, and that makes it a namespace package.

I'm not exactly sure why it works in 2.7, frankly. <time passes> Looking some more: it's because they're playing tricks in a .pth file. I don't recall what the interactions between .pth and namespace packages.

I don't know if Google really means for "google" to be a namespace package, or if it's just a side effect of how they're installing protobuf.

In any event, I don't think we want a _NamespacePath to be modifiable.