Wow, that's a great catch with bytearray on py2. Protocols 0-2 are all actually supposed to work with python 2, and I was using 0 from Py3 as it's the default for Py2, and what I want to use during a short transition where both Py3 and Py2 are operating on my pickled data. I was surprised when Py3's protocol 0 output was so different than Py2's protocol 0.

To be "human-readable", I think the protocol would have to be even stricter, omitting the non-printable ASCII characters.

I wonder if protocol 0 was initially ASCII (or even stricter), and then this went out the window or was unintentionally not adhered to when new things like bytearray (2.6) were introduced.