[ python-Bugs-1586448 ] compiler module dont emit LIST_APPEND w/ list comprehension

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Bugs item #1586448, was opened at 2006-10-29 00:58
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Category: Python Library
Group: None
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: sebastien Martini (seb_martini)
Assigned to: Nobody/Anonymous (nobody)
Summary: compiler module dont emit LIST_APPEND  w/ list comprehension

Initial Comment:
In the module compiler, list comprehensions are
implemented without emitting this bytecode.

For example:
>>> src = "[a for a in range(3)]"
>>> co = compiler.compile(src, 'lc1', 'exec')
>>> co

<code object <module> at 0x404927b8, file "lc1", line 1>
>>> dis.dis(co)

  1           0 BUILD_LIST               0
              3 DUP_TOP
              4 LOAD_ATTR                0 (append)
              7 STORE_NAME               1 ($append0)
             10 LOAD_NAME                2 (range)
             13 LOAD_CONST               1 (3)
             16 CALL_FUNCTION            1
             19 GET_ITER
        >>   20 FOR_ITER                16 (to 39)
             23 STORE_NAME               3 (a)
             26 LOAD_NAME                1 ($append0)
             29 LOAD_NAME                3 (a)
             32 CALL_FUNCTION            1
             35 POP_TOP
             36 JUMP_ABSOLUTE           20
        >>   39 DELETE_NAME              1 ($append0)
             42 POP_TOP
             43 LOAD_CONST               0 (None)
             46 RETURN_VALUE
>>> co2 = compile(src, 'lc2', 'exec')
>>> co2

<code object <module> at 0x40492770, file "lc2", line 1>
>>> dis.dis(co2)

  1           0 BUILD_LIST               0
              3 DUP_TOP
              4 STORE_NAME               0 (_[1])
              7 LOAD_NAME                1 (range)
             10 LOAD_CONST               0 (3)
             13 CALL_FUNCTION            1
             16 GET_ITER
        >>   17 FOR_ITER                13 (to 33)
             20 STORE_NAME               2 (a)
             23 LOAD_NAME                0 (_[1])
             26 LOAD_NAME                2 (a)
             29 LIST_APPEND
             30 JUMP_ABSOLUTE           17
        >>   33 DELETE_NAME              0 (_[1])
             36 POP_TOP
             37 LOAD_CONST               1 (None)
             40 RETURN_VALUE 

-- 
sébastien martini

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