[Numpy-discussion] Support for understand ctypes data-types now in SVN
Stefan van der Walt
stefan at sun.ac.za
Fri Nov 17 14:05:34 CST 2006
On Fri, Nov 17, 2006 at 12:43:45PM -0700, Travis Oliphant wrote:
>
> The NumPy dtype command now understands ctypes data-types including
> derived structures and arrays.
>
> This means you can specify data-types using ctypes method of building
> structures and pass those classes whenever NumPy expects a data-type
> object.
>
> Simple example:
>
> import ctypes as ct
> import numpy as np
>
> np.array([1,2,3],ct.c_short)
>
> More complicated:
>
> class POINT(ct.Structure):
> _fields_ = [("x", ct.c_int),
> ("y", ct.c_int)]
>
> np.array([(3,4),(5,6),(7,8)], dtype=POINT)
Is the memory layout of the array above the same as what an array of
POINTs would be in C, or are they not padded? If not, is
dtype(POINT,align=True) supported?
Or am I rather looking for
dtype(POINT*3,align=True)
or are they equivalent in terms of memory use?
The reason I ask is because this would make it very easy to allocate
fairly complex C structures on the python side when wrapping.
Good stuff, thanks!
Cheers
Stéfan
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