[thelazydogsback]

It amazes me that the stack-entwined implementation with the GIL remained the canonical version this whole time -- I would think that the Stackless version (or similar) would have been the default long-ago. This really should have made it worth it from a 2.x to 3.x version perspective, even if many people had to rewrite their extensions, and even if some monkey-patching were removed from the language in favor of more disciplined meta-programming.

[beagle3]

Stackless still uses the GIL; But it avoids using the C stack most of the time, which opens the door to green threads (of which you can have a lot more than OS threads), suspending processes (dump/undump style, except portably), coroutines and more.

There were a couple of GIL-less variations, but they were either incredibly slow, or suffered serious compatibility problems (and often both).