Python and C

[Gilles Ansquer]

Paul Prescod <paul at prescod.net> wrote in message news:<mailman.146.1077391155.27104.python-list at python.org>...
> hermes at numericable.fr wrote:
> 
> > Hi, this may be a newbie question, as I'm quite new to python but I'd rather get
> > your points of view instead of wasting a week or two on a wrong way 
> > 
> > I'm using python 2.3 on a mandrake brand new system 
> > 
> > My problem : I'd like to use a complex C program under python. 
> > After few researchs I tested SWIG, which seems to work for me exept that I'd
> > like to be able to 
> > use a C function under python that has this prototype 
> > 
> > void Fitimp(double *x1, double *x2... ) 
> 
> How will the implementation of Fitimp know how long these lists are?
> 
> > these double parameters are lists of double precision number.
> > The python script will read this datas from files, So i'd like to know how to
> > transform a python list of double precision float to a C double * variable
> 
> I don't know SWIG but I do know Pyrex, so here's a Pyrex solution:
> 
> import array
> 
> cdef extern from "header.h":
>          cdef void Fitimp(double *x1, int x1_len, double *x2, int x2_len)
> 
> def PyFitimp(pyx1, pyx2):
>          cdef double *x1, *x2
>          cdef int address1, length1, address2, length2
> 
>          array1 = array.array('d', pyx1)
>          address1, length1 = array1.buffer_info()
>          x1 = <double *>address1
> 
>          array2 = array.array('d', pyx2)
>          address2, length2 = array2.buffer_info()
>          x2 = <double *>address2
> 
>          print x1[0]
>          print array1
>          print x2[0]
>          print array2
> 
>          Fitimp(x1, length1, x2, length2)
> 
> PyFitimp(range(3,10), range(6,13))
> 
>   Paul Prescod



thanks for your help, it works really fine, 

altough I'm still having problem because I need to do multiple calls
to this function.
This bring the problem of freeing memory between two calls, is there
any specific way to do do it ? (I get a seg fault when I attempt
multiple calls
from python whereas it does not segfault with multiple C calls.)


Gilles Ansquer