[Numpy-discussion] NumPy C-API equivalent of np.float64()

Matthew Brett matthew.brett@gmail....
Wed Dec 29 13:43:22 CST 2010


Hi,

>> That might be because I'm not understanding you very well, but I was
>> thinking that:
>>
>> cdef dtype descr = PyArray_DescrFromType(NPY_FLOAT64)
>>
>> would give you the float64 dtype that I thought you wanted?  I'm
>> shooting from the hip here, in between nieces competing for the
>> computer and my attention.
>
> I think I need a function. One that does this:
>
>>> n = 10.0
>>> hasattr(n, 'ndim')
>   False
>>> m = np.float64(n)
>>> hasattr(m, 'ndim')
>   True

Now the nieces have gone, I see that I did completely misunderstand.
I think you want the C-API calls to be able to create a 0-dim ndarray
object from a python float.

There was a thread on C-API array creation on the cython list a little
while ago:

http://www.mail-archive.com/cython-dev@codespeak.net/msg07703.html

Code in scipy here:

https://github.com/scipy/scipy-svn/blob/master/scipy/io/matlab/mio5_utils.pyx

See around line 36 there, and 432, and the header file I copied from
Dag Sverre:

https://github.com/scipy/scipy-svn/blob/master/scipy/io/matlab/numpy_rephrasing.h

As you can see, it's a little horrible, in that you have to take care
to get the references right to the dtype and to the data.  I actually
did not investigate in detail whether this lower-level array creation
was speeding my code up much.

I hope that's more useful...

Matthew


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