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

[Lennart Regebro]

On Wed, Feb 13, 2013 at 4:02 PM, Amaury Forgeot d'Arc
<amauryfa at gmail.com> wrote:
> 2013/2/13 Lennart Regebro <regebro at gmail.com>
>>
>> On Wed, Feb 13, 2013 at 3:27 PM, Amaury Forgeot d'Arc
>> <amauryfa at gmail.com> wrote:
>> > Yes, it's jitted.
>>
>> Admittedly, I have no idea in which cases the JIT kicks in, and what I
>> should do to make that happen to make sure I have the best possible
>> real-life test cases.
>
>
> PyPy JIT kicks in only after 1000 iterations.

Actually, my test code mixed iterations and string length up when
printing the results, so the tests I showed was not 100 iterations
with 10.000 long string, but 10.000 iterations with 100 long strings.

No matter what the iteration/string length is .format() is the slowest
or second slowest of all string concatenation methods I've tried and
'%s%s' % just marginally faster. This both on PyPy and CPython and
irrespective of string length.

I'll stick my neck out and say that using formatting for concatenation
is probably an anti-pattern.

//Lennart