Re: [f2py] Frotran, GDAL and f2py

You can call Python from Fortran, but f2py is not involved. I am doing
it and it works rather well for me. Unfortunately, it can get a bit
complicated. I have attached an example. Relevant documentation is The
Python/C API , Extending and embedding Python and the c-api section from
the Numpybook.

It may seem like a lot of work, but for me it was worth it. And it's not
that hard once you get the hang of it.

Stiaan


On 03/02/2010 02:27 AM, Robin wrote:
> On Mon, Mar 1, 2010 at 11:21 PM, Jamie Lahowetz <[email protected]> wrote:
>   
>> Thanks for the reply. Its nice to know that there are other packages for
>> shapefile manipulation. GDAL is an opensource GIS package that does
>> everything I need it to do so there is no real benifit in learning a new
>> package. My first question still stands though: How do I call python from
>> fortran using f2py?
>>     
> I don't think you really can. f2py is designed to allow calling
> fortran code from python as a python extension. I think there is a
> facility for callbacks to python from the fortran code, but I don't
> think that can be used in a standalone way (without calling the
> fortran code as an extension from a python process).
>
> I think the idea is one can write the wrapping stuff (including file
> io etc.) in Python which is faster to write but slower to run, and
> then implement any computationally expensive inner loops in fortran
> which are called easily from the python process.
>
> I don't know of any way to call python from a standalone fortran
> program (other than through a shell). In C it is possible to embed a
> python interpreter in another process, to use python from a c program,
> but I am not aware of anything similar for fortran. Possibly you could
> embed Python in your own C library and interact with that from fortran
> but I think it would be quite complicated.
>
> Cheers
>
> Robin
>
>   
>> On Mon, Mar 1, 2010 at 2:59 PM, James Boyle <[email protected]> wrote:
>>     
>>> As part of Jeff Whittaker's Basemap toolkit for matplotlib, there is a
>>> ability to read/write shapefiles.
>>> The ability to write shapefiles in not cited in the online docs, but there
>>> is an example in the download.
>>> I have only used the read so YMMV.
>>> Jeff is a meteorologist and his stuff is very useful in that field.
>>> http://matplotlib.sourceforge.net/
>>> http://matplotlib.sourceforge.net/users/toolkits.html
>>> --Jim
>>> On Mar 1, 2010, at 12:27 PM, Jamie Lahowetz wrote:
>>>
>>> I have a fortran program that creates storm tracks. I can output these
>>> tracks into a csv file but it would be really helpful if I could just create
>>> shapefiles instead. So heres my question(s):
>>> 1. Im very new to f2py and from what I read, python can be called from
>>> fortran using f2py. I looked at the examples in the documentation but dont
>>> fully understand how to really do this. Can anyone help me out by maybe
>>> explaining it or perhaps share an example of python being called from a
>>> Fortran program.
>>> 2. Is it even possible to do the above using the GDAL python bindings?
>>>
>>> --
>>> Jamie Ryan Lahowetz
>>> University of Nebraska - Lincoln
>>> Graduate Student - Geosciences
>>> 402.304.0766
>>> [email protected]
>>> _______________________________________________
>>> f2py-users mailing list
>>> f2py-users-Y4l6ocDipWCuvFJfX82//[email protected]
>>> http://*cens.ioc.ee/mailman/listinfo/f2py-users
>>>
>>>
>>> _______________________________________________
>>> f2py-users mailing list
>>> f2py-users-Y4l6ocDipWCuvFJfX82//[email protected]
>>> http://cens.ioc.ee/mailman/listinfo/f2py-users
>>>
>>>       
>>
>>
>> --
>> Jamie Ryan Lahowetz
>> University of Nebraska - Lincoln
>> Graduate Student - Geosciences
>> 402.304.0766
>> [email protected]
>>
>> _______________________________________________
>> f2py-users mailing list
>> f2py-users-Y4l6ocDipWCuvFJfX82//[email protected]
>> http://cens.ioc.ee/mailman/listinfo/f2py-users
>>
>>
>>     
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> f2py-users mailing list
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>

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#include <python2.6/Python.h>
#include "/usr/lib64/python/site-packages/numpy/core/include/numpy/arrayobject.h"

#include <string.h>

void init_py_(char *pyfilename, int *pyfilename_len);
void py_foo_(double *args, int *nargs, double *result);

int initialized = 0;
PyObject *pymod, *dict;
PyObject *py_foo;

void init_py_(char *pyfilename, int *pyfilename_len) {
    char pyexecstring[30] = "execfile('";
    char *lastbit = "')\n";

    if (!initialized) {
        initialized = 1;

        Py_Initialize();
        import_array();

        pyfilename[*pyfilename_len] = '\0';

        strcat(pyexecstring, pyfilename);
        strcat(pyexecstring, lastbit);
        PyRun_SimpleString(pyexecstring);

        pymod = PyImport_AddModule("__main__");
        dict = PyModule_GetDict(pymod);
        py_foo = PyDict_GetItemString(dict, "foo");
    }
}

void py_foo_(double *args, int *nargs, double *result) {
    PyObject *foo_args_array;
    PyObject *foo_args;
    PyObject *foo_result;

    foo_args_array = PyArray_SimpleNewFromData(1, (void*)nargs, NPY_DOUBLE, args);
    foo_args = PyTuple_Pack(2, foo_args_array, PyInt_FromLong(*nargs));

    foo_result = PyObject_CallObject(py_foo, foo_args);
    if(!PyArg_ParseTuple(foo_result, "d", result)) {
        printf("Error: ParseTuple failed.\n");
    }

}

program main

character*25 pyfname
integer pyfname_len

double precision args(2), result
integer nargs

pyfname = "pylib.py"
pyfname_len = 8

write (*,"(A)") "Initializing Python"
call init_py(pyfname,pyfname_len)

args(1) = 2d0
args(2) = 3.5
nargs = 2

write (*,"(A)") "Calling Python"
call py_foo(args, nargs, result)

write (*,"(F4.2)") result

end program

py2f: glue.o main.o
	gfortran -lpthread -ldl -lutil -lm -lpython2.6 -o py2f glue.o main.o

main.o: main.f95
	gfortran -c main.f95 -o main.o

glue.o: glue.c
	gcc -c glue.c -o glue.o

#!/usr/bin/python

def foo(args, nargs):
    for val in args:
        print val
    
    print nargs
    
    return (args[0]*args[1],)