[Numpy-discussion] memory allocation at assignment

Nathaniel Smith njs@pobox....
Thu Jun 28 13:42:33 CDT 2012


On Thu, Jun 28, 2012 at 7:04 PM, Chris Barker <chris.barker@noaa.gov> wrote:
> On Thu, Jun 28, 2012 at 9:06 AM, Pierre Haessig
>
>> On the other hand, just like srean mentionned, I think I also misused
>> the "c[:] = a+b" syntax.
>> I feel it's a bit confusing since this way of writing the assignment
>> really feels likes it happens inplace. Good to know it's not the case.
>
> well, c is being modified in place -- it's the a+b that is creating a new array.
>
> so if you have a c around for another purpose (other than to store the
> result of a+b -- it might make sense to use this approach. Though a
> little faster might be:
>
> c[:] = a
> c += b

That should be faster than c[:] = a + b, but still slower than
np.add(a, b, out=c).

-n


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