Dennis Lee Bieber wrote:
> On Mon, 23 Dec 2013 13:33:08 +1100, Steven D'Aprano
> <steve+comp.lang.pyt...@pearwood.info> declaimed the following:
>
>>Roy Smith wrote:
>>
>>
>>> else:
>>> assert 0, "can't create picker (classes = %s)" % classes
>>
>>¡Ay, caramba! I was with you until the very last line. The above code is
>>possibly buggy and inappropriately designed. (I may be completely
>>misinterpreting this, in which case feel free to ignore the following
>>rant.)
>>
>
> I'd think the biggest problem with this is that if one runs Python with
> optimization turned on, the assert statement itself vanishes, leaving one
> with an empty else clause...
>
> Try debugging that problem!
Actually, that's not correct. If the assert statement vanishes, so does the
else clause, since there's nothing in it.
[steve@ando ~]$ python2.7 -c "from dis import dis
> code = compile('''\
> for x in [1, 2, 3]:
> pass
> else:
> assert x
> ''', '', 'exec')
> dis(code)"""
1 0 SETUP_LOOP 35 (to 38)
3 LOAD_CONST 0 (1)
6 LOAD_CONST 1 (2)
9 LOAD_CONST 2 (3)
12 BUILD_LIST 3
15 GET_ITER
>> 16 FOR_ITER 6 (to 25)
19 STORE_NAME 0 (x)
2 22 JUMP_ABSOLUTE 16
>> 25 POP_BLOCK
4 26 LOAD_NAME 0 (x)
29 POP_JUMP_IF_TRUE 38
32 LOAD_GLOBAL 1 (AssertionError)
35 RAISE_VARARGS 1
>> 38 LOAD_CONST 3 (None)
41 RETURN_VALUE
Compare to the case with optimizations on:
[steve@ando ~]$ python2.7 -O -c "from dis import dis
code = compile('''\
for x in [1, 2, 3]:
pass
else:
assert x
''', '', 'exec')
dis(code)"""
1 0 SETUP_LOOP 23 (to 26)
3 LOAD_CONST 0 (1)
6 LOAD_CONST 1 (2)
9 LOAD_CONST 2 (3)
12 BUILD_LIST 3
15 GET_ITER
>> 16 FOR_ITER 6 (to 25)
19 STORE_NAME 0 (x)
2 22 JUMP_ABSOLUTE 16
>> 25 POP_BLOCK
4 >> 26 LOAD_CONST 3 (None)
29 RETURN_VALUE
--
Steven
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