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

[7stud]

On May 8, 11:05 pm, a... at mac.com (Alex Martelli) wrote:
> alf <ask at me> wrote:
> > two ways of achieving the same effect
>
> > l+=[n]
>
> > or
>
> > l.append(n)
>
> > so which is more pythonic/faster?
>
> .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?