[Pyrex] getting data pointer to numpy object

[Brian Blais]

Greg Ewing wrote:
> Brian Blais wrote:
> 
>> ...but I would like to do something like...
>>
>> #-------------------------------
>> def test2(d):  # pass a python dict
>>
>>     w=d['w']   # get the numpy object
>>
>>     cdef double *w_p
>>
>>     # get the pointers
>>     w_p=<double *>w.data
>> #-------------------------------
> 
> You can declare any variable as an ArrayType,
> not just parameters. So
> 
>   def test2(d):
>     cdef ArrayType w
>     cdef double *w_p
>     w = d['w']
>     w_p = <double *>w.data
> 

I tried this, and got some warnings, and the code didn't work. I get the compile-time
warning of:

test3.c:78: warning: use of cast expressions as lvalues is deprecated

(along with all of the other, normal, Pyrex compile warnings)

I am including the code here:


#test3.pyx

cdef extern from "numpy/arrayobject.h":

   struct PyArray_Descr:
     int type_num, elsize
     char type

   ctypedef class numpy.ArrayType [object PyArrayObject]:
     cdef char *data
     cdef int nd
     cdef int *dimensions, *strides
     cdef object base
     cdef PyArray_Descr *descr
     cdef int flags

def fun1(d):


     cdef ArrayType W
     cdef double *w
     cdef int i,l

     W=d['w']
     w=<double *>W.data
     l=W.dimensions[0]*W.dimensions[1]

     for i from 0 <= i < l:

         print "%.4e" % w[i]


#=================================================

#run_test3.py
import numpy
import test3

w=numpy.arange(0,2,.5)
d={"w":w}

test3.fun1(d)


#===================================================

#output from program:
>>> execfile('run_test3.py')
0.0000e+00
5.0000e-01
1.0000e+00
1.5000e+00
8.3394e-312
0.0000e+00
0.0000e+00
0.0000e+00
0.0000e+00
0.0000e+00
0.0000e+00
0.0000e+00
0.0000e+00
0.0000e+00
0.0000e+00
0.0000e+00
0.0000e+00
1.9354e+01
5.3216e-315
0.0000e+00
2.1127e+01
5.3428e-315
0.0000e+00
0.0000e+00
0.0000e+00
0.0000e+00
0.0000e+00
0.0000e+00
0.0000e+00
0.0000e+00
-5.1923e+00
2.5548e+02




-- 
-----------------

             bblais at bryant.edu
             http://web.bryant.edu/~bblais