[Numpy-discussion] Using arr.dtype.type to check byteorder-independed dtype fails for bool
Timothy Hochberg
tim.hochberg at ieee.org
Tue Nov 13 11:17:13 EST 2007
On Nov 13, 2007 6:57 AM, Sebastian Haase <haase at msg.ucsf.edu> wrote:
> On Nov 13, 2007 2:18 PM, Stefan van der Walt <stefan at 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....)
Out of curiosity, does it work with arr.dtype.type == N.float? I would
expect not, and I imagine that is the same reason that it doesn't work for
N.bool. Which is that N.bool is __builtin__.bool or, in other words,
N.boolis just Python's boolean type. I believe this is to protect
those foolish
enough to use "from x import *". Anyway, N.bool_ is the real, numpy boolean
dtype that is analogous to unit8 and friends.
>
>
> Thanks,
> Sebastian
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>
--
. __
. |-\
.
. tim.hochberg at ieee.org
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