Farshid Lashkari wrote:
>>I really don't understand why it's so important: it's not a part of the
>>language definition at all, and therefore whatever behavior you see is
>>simply an artifact of the implementation you observe.
>
>
> I guess I should rephrase my question in the form of an example. Should
> I assume that a new string object is created in each iteration of the
> following loop?
>
> for x in xrange(1000000):
> func(x,'some string')
>
> Or would it be better to do the following?
>
> stringVal = 'some string'
> for x in xrange(1000000):
> func(x,stringVal)
>
> Or, like you stated, is it not important at all?
>
It doesn't make a lot of difference:
>>> import dis
>>> print dis.dis.__doc__
Disassemble classes, methods, functions, or code.
With no argument, disassemble the last traceback.
>>> help(dis.dis)
>>> dis.dis(compile("""\
... for x in xrange(1000000):
... func(x,'some string')""", "", 'exec'))
1 0 SETUP_LOOP 33 (to 36)
3 LOAD_NAME 0 (xrange)
6 LOAD_CONST 0 (1000000)
9 CALL_FUNCTION 1
12 GET_ITER
>> 13 FOR_ITER 19 (to 35)
16 STORE_NAME 1 (x)
2 19 LOAD_NAME 2 (func)
22 LOAD_NAME 1 (x)
25 LOAD_CONST 1 ('some string')
28 CALL_FUNCTION 2
31 POP_TOP
32 JUMP_ABSOLUTE 13
>> 35 POP_BLOCK
>> 36 LOAD_CONST 2 (None)
39 RETURN_VALUE
>>> dis.dis(compile("""\
... stringVal = 'some string'
... for x in xrange(1000000):
... func(x,stringVal)""", "", 'exec'))
1 0 LOAD_CONST 0 ('some string')
3 STORE_NAME 0 (stringVal)
2 6 SETUP_LOOP 33 (to 42)
9 LOAD_NAME 1 (xrange)
12 LOAD_CONST 1 (1000000)
15 CALL_FUNCTION 1
18 GET_ITER
>> 19 FOR_ITER 19 (to 41)
22 STORE_NAME 2 (x)
3 25 LOAD_NAME 3 (func)
28 LOAD_NAME 2 (x)
31 LOAD_NAME 0 (stringVal)
34 CALL_FUNCTION 2
37 POP_TOP
38 JUMP_ABSOLUTE 19
>> 41 POP_BLOCK
>> 42 LOAD_CONST 2 (None)
45 RETURN_VALUE
>>>
It just boils down to either a LOAD_CONST vs. a LOAD_NAME - either way
the string isn't duplicated.
regards
Steve
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Steve Holden +44 150 684 7255 +1 800 494 3119
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