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Sat Sep 2 13:38:05 EDT 2017 · https://mail.python.org/pipermail/python-dev/2017-September/149137.html

On Fri, Sep 1, 2017 at 6:16 PM, Joe Jevnik via Python-Dev <
python-dev at python.org> wrote:

> The string concat optimization happens in the interpreter dispatch for
> INPLACE_ADD
>

In that case, isn't there a new string being build, all in one line of
python? that is, the string the optimization is being created at that
point, so the interpreter can know there isn't anything referencing it
anywhere else.

-CHB

> On Fri, Sep 1, 2017 at 9:10 PM, Greg Ewing <greg.ewing at canterbury.ac.nz>
> wrote:
>
>> Chris Angelico wrote:
>>
>>> This particular example is safe, because the arguments get passed
>>> individually - so 'args' has one reference, plus there's one more for
>>> the actual function call
>>>
>>
>> However, that's also true when you use the += operator,
>> so if the optimisation is to trigger at all in any useful
>> case, the refcount threshold needs to be set higher than
>> 1.
>>
>> Some experiments I did suggest that if you set it high
>> enough for x += y to trigger it, then it will also be
>> triggered in Joe's case.
>>
>> BTW, isn't there already a similar optimisation somewhere
>> for concatenating strings? Does it still exist? How does
>> it avoid this issue?
>>
>> --
>> Greg
>>
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>
>
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>

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[Python-Dev] Inplace operations for PyLong objects