The moment you need to do something that there's not extension coverage for, or the extension primitive is too small, you're contending the GIL. It's pretty ni

The moment you need to do something that there's not extension coverage for, or the extension primitive is too small, you're contending the GIL. It's pretty nice to be able to just throw cores at a problem during prototyping phases, compared to throwing developer time to write native code. This is a real problem-- which is why there's a whole lot of numpy/scipy maintainers in favor of the change.