Dietrich's answer is probably just the thing you need for what you describe, sending bytes, but a closer analogue to the code you've provided for example would be using the bytearray type.
>>> key = bytearray([0x13, 0x00, 0x00, 0x00, 0x08, 0x00])
>>> bytes(key)
b'\x13\x00\x00\x00\x08\x00'
>>>