The open() method in the MSP430Library class takes a string argument for the port. However, in Python 3 the call to MSP430_Initialize() requires a bytes argument, not a string argument. Changing this line:
status = MSP430_Initialize(port, ctypes.byref(version))
to this:
status = MSP430_Initialize(bytes(port, encoding='ascii'), ctypes.byref(version))
is one way to fix the problem.