[Numpy-discussion] memory allocation at assignment

[Nathaniel Smith]

On Thu, Jun 28, 2012 at 12:38 AM, astronomer <shailendra.vikas at gmail.com> wrote:
>
> Hi All,
> I am wondering if there any difference in memory overhead between the
> following code.
> a=numpy.arange(10)
> b=numpy.arange(10)
> c=a+b
>
> and
> a=numpy.arange(10)
> b=numpy.arange(10)
> c=numpy.empty_likes(a)
> c[:]=a+b
>
> Does the later code make a temproray array for the result of (a+b) and then
> copy it to c. I beleive it does that, but i wanted to make sure.

Yes it does. If you want to avoid this extra copy, and have a
pre-existing output array, you can do:

np.add(a, b, out=c)

('+' on numpy array's is just a synonym for np.add; np.add is a ufunc,
and all ufunc's accept this syntax:
  http://docs.scipy.org/doc/numpy/reference/ufuncs.html
)

-n