[Python-3000] struni and the Apple four-character-codes

[Jeffrey Yasskin]

I'm looking through a couple of the OS X tests and have run into the
question of what to do with four-character codes. (For those of you
who are unfamiliar with these, Apple, around the dawn of time, decided
that C constants like 'TEXT' (yes, those are single quotes) would
compile to the uint32_t 0x54455854 (or maybe the other-endian version
of that) so they could use these as cheap-but-readable type
identifiers.) In Python 2, these are represented as 'str' instances,
which PyMac_GetOSType() in Python/mactoolboxglue.c converts to the
native int format. For Python 3, right now they're str8's, but str8 is
theoretically supposed to go away. Because they're binary constants
displayed as ASCII, not unicode text, I initially thought that 'bytes'
was the appropriate type. Unfortunately, bytes is mutable, and I think
it makes sense to hash these constants (and some code in aepack.py
does).

So, I'm stuck and wanted to ask the list for input. I see 5 options:
 1) Make these str instances so they're immutable and just rely on
convention and runtime errors to keep them in ascii.
 2) Make them bytes, and cast them to something else when you want to
make them keys in a dict.
 3) Keep them str8 and give up on getting rid of it.
 4) Make bytes immutable, add a 'buffer' type which acts like the
current bytes type, and make these codes instances of bytes. [probably
impossible this late in the game]
 5) Make a new hashable class for these codes which converts them to
and from ints and bytes and becomes the general argument type for the
apple platform interface. [Cleanest, but lots of work that I'm not
volunteering to do]

Thoughts?
Jeffrey