Running a Fortran function from Python

This example shows how to run a Fortran function from Python.

Setup

Install scipy package. It includes the f2py utility that we will use.

pip3 install scipy

Clone this repository.

git clone https://github.com/evgenyneu/FortranFromPython.git
cd FortranFromPython

Fortran function

We have a simple Fortran function that receives two integer numbers and returns their sum. Our goal is to run this function from Python.

function add(a, b) result(result)
    integer     :: a
    integer     :: b
    integer     :: result
    result = a + b
end function add

Verify f2py utility version

You've installed scipy package that includes the f2py. There are two incompatible versions of Python: Python2 and Python3. We need to make sure that when we type f2py command it executes the Python3 version of this utility.

which f2py

It will show the location of the utility, usually something like

/Library/Frameworks/Python.framework/Versions/3.6/bin/f2py

You can see that utility belongs to Python 3.6, which means we use the correct one. If the returned location corresponds to Python 2, then you will need to look at your .bash_profile (on Mac) and add Python3 binaries directory to the PATH variable.

Generate Python module from Fortran code

Change to the fortran directory of this repository and build a Python extension module:

f2py -c -m add_two_numbers add_two_numbers.f90

Run Fortran code from Python

The f2py utility will generate a module file that can be imported into Python code. To check that it is working, open python console from the fortran directory:

python3
>>> import add_two_numbers
>>> add_two_numbers.add(1,41)
42

Run Fortran code from a unit test

The Fortran code is also executed from the unit test.

Install pytest:

pip3 install pytest

From the root directory of this repository, run

pytest

Reference

• Using Python as glue