Basically you just want to kick the malloc implementation into doing
some housekeeping, freeing its caches?  I'm kinda surprised you don't
add the hook directly to your libc's malloc.

IMO, there's no use-case for this until Py_Finalize can completely tear
down the interpreter, which requires a lot of special work (killing(!)
daemon threads, unloading C modules, etc), and nobody intends to do that
at this point.

The practical alternative, as I said, is to run python in a subprocess.
 Let the OS clean up after us.