[Numpy-discussion] problem with view() and strided arrays?

Charles R Harris charlesr.harris@gmail....
Thu Apr 24 22:53:42 CDT 2008


On Thu, Apr 24, 2008 at 10:00 AM, Zachary Pincus <zachary.pincus@yale.edu>
wrote:

> > It seems like 'view' won't create a view where the stride length is
> > not a whole multiple of the dtype's itemsize. However, since strides
> > are measured in bytes (right?), this shouldn't be a problem.
>
>
> Actually -- it seems like view() doesn't work with strided arrays at
> all. (?)
>
> In : a = numpy.ones((4,32), dtype=numpy.uint8)
>
> In : a.view(numpy.uint16).shape
> Out: (4, 16)
>
> In : a[:,:16].view(numpy.uint16)
> ValueError: new type not compatible with array.
>
> I think this might be a recent regression, because before I updated my
> numpy installation to the latest SVN version (to check if the bug was
> fixed!), I'm pretty sure this kind of operation worked.
>

Views only work for items of the same size. You are trying to view bytes as
two byte values. View is like strict pointer aliasing in C.

Chuck
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