which is more pythonic/faster append or +=[]

[Stargaming]

Alex Martelli schrieb:
> 7stud <bbxx789_05ss at yahoo.com> wrote:
>    ...
> 
>>>.append - easy to measure, too:
>>>
>>>brain:~ alex$ python -mtimeit 'L=range(3); n=23' 'x=L[:]; x.append(n)'
>>>1000000 loops, best of 3: 1.31 usec per loop
>>>
>>>brain:~ alex$ python -mtimeit 'L=range(3); n=23' 'x=L[:]; x+=[n]'
>>>1000000 loops, best of 3: 1.52 usec per loop
>>>
>>>Alex
>>
>>Why is it necessary to copy L?
> 
> 
> If you don't, then L gets longer and longer -- to over a million
> elements by the end of the loop -- so we're measuring something that's
> potentially very different from the problem under study, "what's the
> best way to append one item to a 3-items list".
> 
> That's important to consider for any microbenchmark of code that changes
> some existing state: make sure you're measuring a piece of code that
> _overall_ does NOT change said existing state in a cumulative way,
> otherwise you may be measuring something very different from the issue
> of interest.  It's maybe the only important caveat about using "python
> -mtimeit".
> 
> 
> Alex
>  

Cannot reproduce that. Consider the following:

$ python -mtimeit "L=range(3)" "L.append(1); print len(L)"
4
4
[...]
4
1000 loops, best of 3: [...]

Doesn't seem like copying is really neccessary.