With this patch, read_byte returns an integer in the range -128 to 127 instead of 0 to 255 if char is signed. Python 3.1.2 (r312:79149, Mar 21 2010, 00:41:52) [MSC v.1500 32 bit (Intel)] on win32 is affected by this. I think it is a bug. The test code would fail if the test string contained any bytes outside the ASCII range.
(Did this really go unnoticed for a year and a half? I noticed it the moment I first tried to use read_byte (which was just now). I see that read_byte was broken in a different way in 3.0. Does anybody actually use it?)