Convert python long/int to fixed size byte array
With Python 3.2 and later, you can use int.to_bytes and int.from_bytes: https://docs.python.org/3/library/stdtypes.html#int.to_bytes
With Python 3.2 and later, you can use int.to_bytes and int.from_bytes: https://docs.python.org/3/library/stdtypes.html#int.to_bytes