the “strange errors” are actually the byte representation of the numbers. sorry, i forgot about that part. if you change the code (temporarily) to output the byte number rather than the byte at that number, then you will see the numbers.
but, if you get values in the arduino serial monitor when you press buttons, it seems that the arduinome is responding somewhat properly.
did you flash the arduino to reset the serial number? Sorry, i am not familiar with Serial-PyIO