[Numpy-discussion] Using arr.dtype.type to check byteorder-independed dtype fails for bool

Sebastian Haase haase@msg.ucsf....
Tue Nov 13 07:57:49 CST 2007


On Nov 13, 2007 2:18 PM, Stefan van der Walt <stefan@sun.ac.za> wrote:
> Hi Sebastian
>
> On Tue, Nov 13, 2007 at 01:11:33PM +0100, Sebastian Haase wrote:
> > Hi,
> > I need to check the array dtype in a way that it is ignoring
> > differences coming only from big-endian vs. little-endian.
>
> Does
>
> N.issubdtype(first_dtype, second_dtype)
>
> work?

Hi Stéfan !
It appears to work :

>>> N.empty(5, dtype=">f").dtype==N.float32
False
>>> N.empty(5, dtype="<f").dtype==N.float32
True
>>> a = N.empty(5, dtype=">f")
>>> a.dtype
>f4
>>> a.dtype.type
<type 'numpy.float32'>
>>> N.issubdtype(a.dtype, N.float32)
True
>>> a = N.empty(5, dtype=">?")
>>> a.dtype
bool
>>> a = N.empty(5, dtype="<?")
>>> a.dtype
bool
>>> a = N.empty(5, dtype=">?")
>>> N.issubdtype(a.dtype, N.bool)
True
>>> N.issubdtype(a.dtype, N.bool_)
True

Furthermore however,
>>> N.empty(5, dtype=">?").dtype == N.empty(5, dtype="<?").dtype
True

So, for "symmetry reasons" with my existing non-bool code, I would
likely use "arr.dtype.type == N.bool_".
Still wondering what the "_" means here. (reading the book did not
enlighten....)

Thanks,
Sebastian


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