Python 3.9 deprecated API calls in use

Per the Python 3.9 release notes[1], `PyEval_CallFunction` is deprecated

I believe `PyObject_CallFunction` is the preferred replacement[2].

[1]
https://docs.python.org/3/whatsnew/3.9.html#deprecated

[2]
https://docs.python.org/3/c-api/call.html?highlight=pyobject_callfunction#c.PyObject_CallFunction
