[f2py] f2py with commonblocks - problem

[Pearu Peterson]

On Tue, July 22, 2008 10:43 am, Jan.Sippli at dlr.de wrote:
> Hello,
> I'm a student at the german aerospace-center in germany.
> I have some problems with wrapping code from fortran to python by using
> common blocks. To show you my problem I paste you some example-fortran
> code. It isn't allowed (to me) to change the source code to solve the
> problem.

The example-fortran code seem to use poor programming style:
the dimensions of the work argument are defined in a common block.
Hmm, it can be also a clever trick for Fortran.. Could you check whether
the original Fortran code uses the same trick? If yes, read on.
Otherwise, fix the example code and run f2py as follows:

  f2py -c --fcompiler=gnu95 sub.f -m test

(note that it does not make sense to wrap the main program to python,
hence main.f is not used in f2py argument list).

>
> When I try to create the python-modul I build the .pyf-file first with the
> following command:
>
> f2py main.f sub.f -m test -h test.pyf
>
> Reading fortran codes...
> 	Reading file 'main.f' (format:fix,strict)
> 	Reading file 'sub.f' (format:fix,strict)
> Post-processing...
> 	Block: test
> 			Block: test
> 			Block: set
> 			Block: compute
> 			Block: output
> Post-processing (stage 2)...
> Saving signatures to file "./test.pyf"
>
>
>
> Then I try to build the .so-file by doing this
>  f2py -c test.pyf main.f sub.f --f90exec=/usr/bin/gfortran

Please use --fcompiler=gnu95 instead of --f90exec switch (otherwise
you'll get undefined symbol errors later).

> But then I get an ERROR when gcc tries  to compile the testmodul.c
> for example "n1,n2 is not defined"

Ok, here follows a workaround:

1) Run
  f2py -m test -h test.pyf sub.f

2) Edit test.pyf file as follows (replace dimension specs n1,n2
by *,*, respectively). Here's the content of resulting test.pyf file:

python module test ! in
    interface  ! in :test
        subroutine set ! in :test:sub.f
            integer :: n1
            integer :: n2
            common /sizes/ n1,n2
        end subroutine set
        subroutine compute(work) ! in :test:sub.f
            real dimension(*,*) :: work
        end subroutine compute
        subroutine output(work) ! in :test:sub.f
            real dimension(*,*) :: work
        end subroutine output
    end interface
end python module test

3) Run

  f2py -c test.pyf sub.f --fcompiler=gnu95

4) In python:

>>> from numpy import *
>>> import test
>>> test.set()
>>> work = zeros((test.sizes.n1, test.sizes.n2),dtype='f',order='FORTRAN')
>>> test.compute(work)
>>> print work
>>> test.output(work)

Note that dtype='f' and order='FORTRAN' options are crucial to use.

HTH,
Pearu