I was having some issues earlier wrapping my mind around why, exactly, packing strings didn't give me a string with the "\x##\x##\x##" format. Evidently, that is only necessary for characters that do not have a normal, printable equivalent.
>>> "\x7D" + "\x7B"
Anyway, the following output is what had me confused, and why I spent about an hour or so now looking into the 'struct' package and why it wasn't giving me what I thought I wanted. Notice the plaintext "test" at the end. It seemed out of place, so I was assuming that I was doing something wrong.
>>> from pcsextension.payload import payload
>>> from pcs.packets.tcp import tcp
>>> p = payload('test')
>>> t = tcp()
>>> t.data = p