[Python-Dev] New opcode to simplifiy/speedup list comprehensions

[Raymond Hettinger]

> >>> def f(x):
> 	y = [i+i for i in x]
> 
> >>> dis(f)
>   2           0 BUILD_LIST               0
>               3 DUP_TOP
>               4 LOAD_ATTR                0 (append)    <-- delete this
> line
>               7 STORE_FAST               3 (_[1])
>              10 LOAD_FAST                0 (x)
>              13 GET_ITER
>         >>   14 FOR_ITER                20 (to 37)
>              17 STORE_FAST               2 (i)
>              20 LOAD_FAST                3 (_[1])
>              23 LOAD_FAST                2 (i)
>              26 LOAD_FAST                2 (i)
>              29 BINARY_ADD
>              30 CALL_FUNCTION            1              --> replace
with
> LIST_APPEND
>              33 POP_TOP                                 <-- delete
this
> line
>              34 JUMP_ABSOLUTE           14
>         >>   37 DELETE_FAST              3 (_[1])


P.S.  The patch also removes the DELETE_FAST at position 37


>              40 STORE_FAST               1 (y)
>              43 LOAD_CONST               0 (None)
>              46 RETURN_VALUE


Raymond Hettinger