objc._pycoder contains code for archiving Python objects using the NSCoding protocol. Some of these functions aren't necessary because their encoding and decoding is done by C code.
Most functions marked with 'pragma: no cover' can and should be removed, I haven't done this yet because I'm not yet 100% sure my analysis is correct.
There should be documentation in the file that explains why some basic types appear to be missing in the encoding table.
ALSO: look into python 3.3 pickle changes (there could be a protocol change for python sets)