[Python-Dev] Usage of += on strings in loops in stdlib

[Christian Tismer]

On 13.02.13 19:06, Maciej Fijalkowski wrote:
> On Wed, Feb 13, 2013 at 7:33 PM, MRAB <python at mrabarnett.plus.com> wrote:
>> On 2013-02-13 13:23, Lennart Regebro wrote:
>>> On Wed, Feb 13, 2013 at 1:10 PM, Serhiy Storchaka <storchaka at gmail.com>
>>> wrote:
>>>> I prefer "x = '%s%s%s%s' % (a, b, c, d)" when string's number is more
>>>> than 3
>>>> and some of them are literal strings.
>>>
>>> This has the benefit of being slow both on CPython and PyPy. Although
>>> using .format() is even slower. :-)
>>>
>> How about adding a class method for catenation:
>>
>>      str.cat(a, b, c, d)
>>      str.cat([a, b, c, d]) # Equivalent to "".join([a, b, c, d])
>>
>> Each argument could be a string or a list of strings.
>>
>>
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> I actually wonder.
>
> There seems to be the consensus to avoid += (to some extent). Can
> someone commit the change to urrllib then? I'm talking about reverting
> http://bugs.python.org/issue1285086 specifically

So _is_ += faster in certain library funcs than ''.join() ?
If that's the case, the behavior of string concat could be something 
that might be added
to some implementation info, if speed really matters.

The library function then could take this info and use the appropriate code
path to always be fast, during module initialisation.
This is also quite explicit, since it tells the reader not to use in-place
add when it is not optimized.

If += is anyway a bit slower than other ways, forget it.
I would then maybe add a commend somewhere that says
"avoiding '+=' because it is not reliable" or something.

cheers - chris

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