Re: [Numpy-discussion] Zeros in strides

[Sasha <nd...@ma...>]

On 2/2/06, Travis Oliphant <oli...@ie...> wrote:
> Sasha wrote:
>
> >Sure.  I've started working on a "proof of concept" patch and will post =
it soon.
> >
> Great.

Attached patch allows numpy create memory-saving zero-stride arrays.

Here is a sample session:

>>> from numpy import *
>>> x =3D ndarray([5], strides=3D0)
>>> x
array([12998768, 12998768, 12998768, 12998768, 12998768])
>>> x[0] =3D 0
>>> x
array([0, 0, 0, 0, 0])
>>> x.strides =3D 4
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
ValueError: strides is not compatible with available memory
>>> x.strides
(0,)
>>> x.data
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
AttributeError: cannot get single-segment buffer for discontiguous array
>>> exp(x)
array([ 1.,  1.,  1.,  1.,  1.])
# Only single-element buffer is required for zero-stride array:
>>> y =3D ones(1)
>>> z =3D ndarray([10], strides=3D0, buffer=3Dy)
>>> z
array([1, 1, 1, 1, 1, 1, 1, 1, 1, 1])


I probably missed some places where buffer size is computed as a
product of dimensions, but it should not be hard to review the code
for those if we agree that having zero-stride arrays is a good idea.

Note that I did not attempt to change any behaviors, the only change
is that zero-stride arrays do not use more memory than they need.