f2py array valued functions

Question

Do recent versions of f2py support wrapping array-valued fortran functions? In some ancient documentation this wasn't supported. How about it now?

Let's for example save the following function as func.f95.

function func(x)
    implicit none
    double precision :: x(:),func(size(x))
    integer :: i
    do i=1,size(x)
        func(i) = i*x(i)
    end do
end function

I compile this with f2py --fcompiler=gnu95 -c -m func func.f95

Then let the following python code be test_func.py

import func
from numpy import array

x = array(xrange(1,10),dtype='float64')
print 'x=',x

y = func.func(x)
print 'func(x)=',y

The output from
python test_func.py is

x= [ 1.  2.  3.  4.  5.  6.  7.  8.  9.]
Segmentation fault

you can do the workaround explained in this answer..., but it will require more evaluations than required. For this case I'd go for Cython — Saullo G. P. Castro
– Saullo G. P. Castro, Commented Aug 13, 2013 at 4:50

SethMMorton · Accepted Answer · 2013-09-09 22:39:49Z

3

The mechanism of f2py turns Fortran subroutines into python functions. It doesn't understand how to turn a Fortran function into a python function. I have found that I need to wrap all Fortran functions with a subroutine, or even better, rewrite them as subroutines.

edited Sep 9, 2013 at 22:39

answered Jun 6, 2012 at 13:52

SethMMorton

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2 Comments

capt Over a year ago

Is f2py that powerful? Is it reliable enough that writing the whole fortran codebase in this special way is a fair price?

SethMMorton Over a year ago

I've never had problems with reliability, but like I said, it is frustrating. Personally, I only use it for small projects because of the restrictions it imposes. There is another tool, fwrap, that is supposed to be better than f2py, but I haven't tested it.

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