[rogerbinns]

Heap allocation does also allow other things. For example stack frames (PyFrame) are also heap allocated. When there is an exception, the C stack gets unwound but the heap allocated frames are retained forming the traceback. You can then examine the values of the local variables at each level of the traceback.

And it also allows async functions, since state is held off the C stack, so frames can be easily switched when returning to the event loop.

The other thing made easy is C extension authoring. You compile CPython without free lists and an address sanitizer, and getting reference counting wrong shows up.