[Pyrex] Re: Pyrex and Numarray

[John Carter]

I've never had any problems doing this.

I have declared a _numarray object which


cdef extern from "numarray/arraybase.h":
     cdef enum NumarrayType:
         tAny, tBool, tInt8, tUInt8, tInt16, tUInt16, tInt32, 
tUInt32, tInt64, tUInt64, tFloat32, tFloat64, tComplex32, tComplex64

cdef extern from "numarray/arrayobject.h":
     struct PyArray_Descr:
         int type_num
         int elsize
         char type

cdef extern from "numarray/arrayobject.h":
     ctypedef class numarray._numarray._numarray [object PyArrayObject]:
         cdef char *data
         cdef int nd
         cdef int *dimensions
         cdef int *strides
         cdef object base
         cdef PyArray_Descr *descr

cdef extern from "numarray/arrayobject.h":
     cdef object PyArray_FromDimsAndData(int nd, int *dims, int type, 
char *data)
     cdef object PyArray_FromDims(int nd, int *dims, int type)
     cdef object PyArray_Return(object)


I can use with

cdef extern from "numarray/libnumarray.h":
     # The numarray initialization funtion
     void import_libnumeric()

# The Numeric API requires this function to be called before
# using any Numeric facilities in an extension module.
import_libnumeric()



cdef _numarray out

then I use the nunarray api to fill it.

   out = PyArray_FromDims(left.nd, left.dimensions, tUInt8)

then I can use the constructs

out.nd, out.dimensions, out.strides, out.data

to access the internals.

this is great but what I really want to do is, given a,b,c,d,e as 
numarray's I want to write

a = (c+b)*(d-e)

and have pyrex generate efficient C code that dosnt create intermediate arrays.

I'm sure  I can do this if a .. e are PyObjects by going back to the 
python level. But that seems to defeat the idea of numerical efficiency.

I ran an undergraduate project about 3 years ago (pyrex was about 
0.4) which did this but it wasn't really useable,as he totally 
hijacked the [] notation and lists and stuff stopped working.

I'm considering having another go (or rather getting an 
undergraduate), but I cant decide on the approach:
Use a preprocessor to generate pyrex,
Hack pyrex internals
or wait till pyrex does objects and hope that the object 
implementation will be sufficiently flexible to let me do what I want.

I'm currently leaning on the first option, even if it means parsing 
the pyrex file twice.

John





Dr. John N. Carter   jnc at ecs.soton.ac.uk
ISIS                        http://www.ecs.soton.ac.uk/~jnc/