> there is a large number of “dark matter” Python (and C extension) code out there that isn’t open-source. We need to be careful not to break it since it might

> there is a large number of “dark matter” Python (and C extension) code out there that isn’t open-source. We need to be careful not to break it since it might not be feasible for its users to make required changes, or to report problems back upstream to us. In particular, some C extensions protect their own internal state with the GIL. This is a big worry, and might be a big hindrance to adoption of a GIL-free Python. Probably doesn't work across minor versions anyway, most stuff isn't built against the limited API.