L[:]

[Grant Edwards]

On 2014-01-10, Terry Reedy <tjreedy at udel.edu> wrote:
> On 1/10/2014 12:38 PM, Albert-Jan Roskam wrote:
>> In Python Cookbook, one of the authors (I forgot who) consistently used the "L[:]" idiom like below. If the second line simply starts with "L =" (so no "[:]") only the name "L" would be rebound, not the underlying object. That was the author?? explanation as far as I can remember. I do not get that. Why is the "L[:]" idiom more memory-efficient here? How could the increased efficiency be demonstrated?
>>
>> #Python 2.7.3 (default, Sep 26 2013, 16:38:10) [GCC 4.7.2] on linux2
>>>>> L = [x ** 2 for x in range(10)]
>>>>> L[:] = ["foo_" + str(x) for x in L]
>
> Unless L is aliased, this is silly code.

And if L _is_ aliaised, it's probably trying to be too clever and
needs to be fixed.

-- 
Grant