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this patch touches only Python/ceval.c.
1. the only existing thing it modifies is PyEval_EvalFrameEx (adds 7
extra cases for the new 3.0 opcodes, doesn't mess w/ any of the existing
ones, or anything else as a matter of fact)
2. that, plus it defines (the new opcodes)
#define SET_ADD 17
#define STORE_LOCALS 69
#define LOAD_BUILD_CLASS 34 // 71 in py3k
#define MAKE_BYTES 35 // unused in py3k
#define POP_EXCEPT 36 // 89 in py3k
#define UNPACK_EX 94
#define BUILD_SET 109 // 104 in py3k
and some backported vars & helper functions
only 2 contiguous areas of ceval.c is patched (1. & 2. - areas are
delimited by the comments '// py3k')
this simple patch seems sufficient in theory to allow the interpreter to
natively execute most of 3.0's language syntax (nonlocal, print,
extended unpacking, ... have been tested to work)
*the one exception being pep3102 - keyword-only arguments
i wrote 2 small scripts which gives an interactive function 'compile_py3k'
similar to __builtin__.compile. its a wrapper function which queries
the byte-compiling task to a python 3.0 server via pipe io.
example demonstrating pep3132 extended unpacking syntax:
a,b,*c = 1,2,3,4
(note the backported 3.0 opcode used in line2 of the disassembly)
Python 2.5.2 (r252:60911, Jun 27 2008, 21:19:51)
[GCC 3.4.6 20060404 (Red Hat 3.4.6-9)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import py3to2
py3to2 server restarting with io: (4, 5)
py3to2 server: Python 3.0b1 (r30b1:64395, Jun 24 2008, 21:53:55)
py3to2 server: [GCC 3.4.6 20060404 (Red Hat 3.4.6-9)] on linux2
py3to2 server: Type "help", "copyright", "credits" or "license" for more
information.
py3to2 server:
>>> src = "a,b,*c = 1,2,3,4"
>>> codeobject = py3to2.compile_py3k(src,"","exec")
 1 0 LOAD_CONST 5 ((1, 2, 3, 4))
 3 UNPACK_EX_py3k 2
 6 STORE_NAME 0 (a)
 9 STORE_NAME 1 (b)
 12 STORE_NAME 2 (c)
 15 LOAD_CONST 4 (None)
 18 RETURN_VALUE
>>> exec(codeobject)
>>> print a,b,c
1, 2, [3, 4]
>>>
u can go c
http://pypi.python.org/pypi?name=py3to2&version=20080628&:action=display
for more info on the script
anyway, i think it would b a great boost for python 3.0 (which i think
is very cool) if developers can test/develop it under the 2.x
environment. this patch plus some scripts to emulated 3k extensions 
(bytes, bytearray, ...) can go a long way in making 3.0 available for
the masses.
ps. i've also attempted the reverse (forward-port 2.x opcodes to 3.0),
& its a bit more complicated (namely the PRINTxxx opcodes). if there's
significant interest in that, i could work on it a bit more, but my
current interest is in extending 3.0 functionality to the vast 2.x
software base.