I'm completely guessing here, but my guess is that regular PyObject arrays require single threaded access with GIL. But if you have pointers to strings without

I'm completely guessing here, but my guess is that regular PyObject arrays require single threaded access with GIL. But if you have pointers to strings without involving Python machinery you don't need the GIL for each access. I would also guess that when using object you actually throw away all the known type information and you have to repeatedly call PyString_Check or similar to do type checks to ascertain they are strings.