[Numpy-discussion] What is a numpy.long type?

David Cournapeau cournape@gmail....
Fri Aug 23 01:57:16 CDT 2013


On Fri, Aug 23, 2013 at 6:02 AM, Chris Barker - NOAA Federal <
chris.barker@noaa.gov> wrote:

> Hi folks,
>
> I had thought that maybe a numpy.long dtype was a system
> (compiler)-native C long.
>
> But on both 32 and 64 bit python on OS-X, it seems to be 64 bit. I'm
> pretty sure that on OS-X 32 bit, a C long is 32 bits. (gdd, of course)
>
> I don't have other machines to test on , but as the MS compilers and
> gcc do different things with a C long on 64 bit platforms, I"m curious
> how numpy defines it.


> In general, I prefer the "explicit is better than implicit" approach
> and use, e.g. int32 and int64. However, in this case, we are using
> Cython, and calling C code that used "long" -- so what I want is
> "whatever the compiler thinks is a long" -- is there  a way to do that
> without my own kludgy platform-dependent code?
>
> I note that the Cython numpy.pxd assigns:
>
> ctypedef signed long      npy_long
>
> Is that a bug? (or maybe npy_long is not supposed to match np.long....
>

npy_long is indeed just an alias to C long, np.long is an alias to python's
long:

arch -32 python -c "import numpy as np; print np.dtype(np.int); print
np.dtype(np.long)"
int32
int64

arch -64 python -c "import numpy as np; print np.dtype(np.int); print
np.dtype(np.long)"
int64
int64

and python -c "import numpy as np; print np.long is long" will print True

All this is on python 2.7, I am not sure how/if that changes on python 3
(that consolidated python int/long).

David

>
> -Chris
>
>
>
>
> --
>
> Christopher Barker, Ph.D.
> Oceanographer
>
> Emergency Response Division
> NOAA/NOS/OR&R            (206) 526-6959   voice
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>
> Chris.Barker@noaa.gov
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