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8 years after the original patch, there's still no trivial constant folding in bytecode generated (because peephole of course is not a real optimizer to consistently catch all cases):
$ cat const.py 
FOO = 1
BAR = FOO + 2 + 4
$ python --version
Python 2.7.3
$ python -OO -m dis const.py
 1 0 LOAD_CONST 0 (1)
 3 STORE_NAME 0 (FOO)
 2 6 LOAD_NAME 0 (FOO)
 9 LOAD_CONST 1 (2)
 12 BINARY_ADD 
 13 LOAD_CONST 2 (4)
 16 BINARY_ADD 
 17 STORE_NAME 1 (BAR)
 20 LOAD_CONST 3 (None)
 23 RETURN_VALUE 
$ python3.3 --version
Python 3.3.3
$ python3.3 -OO -m dis const.py
 1 0 LOAD_CONST 0 (1) 
 3 STORE_NAME 0 (FOO) 
 2 6 LOAD_NAME 0 (FOO) 
 9 LOAD_CONST 1 (2) 
 12 BINARY_ADD 
 13 LOAD_CONST 2 (4) 
 16 BINARY_ADD 
 17 STORE_NAME 1 (BAR) 
 20 LOAD_CONST 3 (None) 
 23 RETURN_VALUE