fortran_oop_from_python

Sample of using fortran classes from python C extension.

• This repository contains sample code to use classes defined in Fortran from Python.
• For the binding between Python and Fortran, I use the C extension of Python.
• Pointers pointing to Fortran classes are included in PyObject as C void*. In this case, PyCapsule_New is used.
• Interoperation is made possible by converting the void* to a Fortran pointer on the fortran side by using c_f_pointer.

Code overview

fortran_oop_lib/m_shape.f90

As an example, we have an interface type,abstruct,public :: IShape that represents the shape, and in the method we have created a function to calculate the area of the shape. We have defined "circle" and "square" as the actual instances.

It also makes use of pure elemental features, so it will be easier to write constructors, etc. when the main code is fortran.

There are also methods to show the data of each class to the console.

pyflib/m_shape_c.f90

This is the C interface of m_shape.f90 defined with iso_c_binding.

pyflib/custom.c

Python C extension code.

include/c_f_interface.h

The functions defined in m_chape_c.f90 in C header format.

test/fort_main.f90

Main program which use fortran_oop_lib/m_shape.f90 for test.

test/test_c_main.c

Main program which use fortran_oop_lib/m_shape.f90 and its binding /pyflib/m_shape_c.f90.

main.py

python test script which load custom.so and use it. custom.so use fortran Circle_t type defined in the fortran_oop_lib/m_shape.f90.

Makefile

make file which build custom.so, f_main and c_main.

How to build and test run

First, build binary file. Then, run tests as follows.

make
./f_main
./c_main
python3 main.py

Output samples

./f_main

#--- scalar version ---
 【 Hello from Fortran showinfo method 】
    type   : Circle_t
    radius :    3.0000000000000000     
    area   :    28.274333882308138     
 【 Hello from Fortran showinfo method 】
    type   : Rectangle_t
    width  :    2.0000000000000000     
    height :    3.0000000000000000     
    area   :    6.0000000000000000     
#--- array version ---
  -- array(1) ---
 【 Hello from Fortran showinfo method 】
    type   : Circle_t
    radius :    1.0000000000000000     
    area   :    3.1415926535897931     
 【 Hello from Fortran showinfo method 】
    type   : Rectangle_t
    width  :    1.0000000000000000     
    height :    4.0000000000000000     
    area   :    4.0000000000000000     
  -- array(2) ---
 【 Hello from Fortran showinfo method 】
    type   : Circle_t
    radius :    2.0000000000000000     
    area   :    12.566370614359172     
 【 Hello from Fortran showinfo method 】
    type   : Rectangle_t
    width  :    2.0000000000000000     
    height :    5.0000000000000000     
    area   :    10.000000000000000     
  -- array(3) ---
 【 Hello from Fortran showinfo method 】
    type   : Circle_t
    radius :    3.0000000000000000     
    area   :    28.274333882308138     
 【 Hello from Fortran showinfo method 】
    type   : Rectangle_t
    width  :    3.0000000000000000     
    height :    6.0000000000000000     
    area   :    18.000000000000000

./c_main

calculatearea(circle) from C : 28.274334
 【 Hello from Fortran showinfo method 】
    type   : Circle_t
    radius :    3.0000000000000000     
    area   :    28.274333882308138     
calculatearea(rectangle) from C : 6.000000
 【 Hello from Fortran showinfo method 】
    type   : Rectangle_t
    width  :    2.0000000000000000     
    height :    3.0000000000000000     
    area   :    6.0000000000000000

python3 main.py

 【 Hello from Fortran showinfo method 】
    type   : Circle_t
    radius :    1.0000000000000000     
    area   :    3.1415926535897931     
 【 Hello from Fortran showinfo method 】
    type   : Circle_t
    radius :    2.0000000000000000     
    area   :    12.566370614359172     
 【 Hello from Fortran showinfo method 】
    type   : Circle_t
    radius :    3.0000000000000000     
    area   :    28.274333882308138     

# ---- get area as PyObject ---
<class 'float'> 3.141592653589793
<class 'float'> 12.566370614359172
<class 'float'> 28.274333882308138