embed Fortran in Python using Cython

c_penjumlahan.f90

module penjumlahan_interface
use iso_c_binding, only: c_double
use penjumlahan_module, only: penjumlahan
implicit none
contains
subroutine c_penjumlahan(a, b, c) bind(c)
    real(c_double), intent(in) :: a, b
    real(c_double), intent(out) :: c
    call penjumlahan(a, b, c)
    
end subroutine c_penjumlahan
    
end module penjumlahan_interface

c_penjumlahan.h

extern void c_penjumlahan(double* a, double* b, double* c);

c_perkalian.f90

module perkalian_interface
use iso_c_binding, only: c_double
use perkalian_module, only: perkalian
implicit none
contains
subroutine c_perkalian(a, b, c) bind(c)
    real(c_double), intent(in) :: a, b
    real(c_double), intent(out) :: c
    call perkalian(a, b, c)
    
end subroutine c_perkalian
    
end module perkalian_interface

c_perkalian.h

extern void c_perkalian(double* a, double* b, double* c);

penjumlahan.f90

module penjumlahan_module
implicit none
contains
subroutine penjumlahan(a, b, c)
    double precision, intent(in) :: a, b
    double precision, intent(out) :: c

    c = a + b
    
end subroutine penjumlahan
    
end module penjumlahan_module

perkalian.f90

module perkalian_module
implicit none
contains
subroutine perkalian(a, b, c)
    double precision, intent(in) :: a, b
    double precision, intent(out) :: c

    c = a * b
    
end subroutine perkalian
    
end module perkalian_module

setup.py

from distutils.core import setup
from distutils.extension import Extension
from Cython.Distutils import build_ext
# This line only needed if building with NumPy in Cython file.
from numpy import get_include
from os import system

# HOW TO RUN SETUP.PY
# python setup.py build_ext -inplace --plat-name=win-amd64
# python setup.py install

def fortran_compiler(statement):
    print(statement)
    system(statement)

# compile the fortran modules without linking
# compile fortran modules
fortran_compiler('gfortran penjumlahan.f90 -c -o penjumlahan.o -O3 -fPIC')
fortran_compiler('gfortran perkalian.f90 -c -o perkalian.o -O3 -fPIC')

# compile fortran shared modules
fortran_compiler('gfortran c_penjumlahan.f90 -c -o c_penjumlahan.o -O3 -fPIC')
fortran_compiler('gfortran c_perkalian.f90 -c -o c_perkalian.o -O3 -fPIC')

# editable components
module_name = "kalkulator"
source_file = "source_file.pyx"
compiled_modules = ['penjumlahan.o', 'perkalian.o', 'c_penjumlahan.o', 'c_perkalian.o']

# setup
ext_modules = [Extension(# module name:
                         module_name,
                         # source file:
                         [source_file],
                         # other compile args for gcc
                         extra_compile_args=['-fPIC', '-O3'],
                         # other files to link to
                         extra_link_args=compiled_modules)]

for e in ext_modules:
    e.cython_directives = {'language_level': "3"} #all are Python-3

setup(name = module_name,
      cmdclass = {'build_ext': build_ext},
      # Needed if building with NumPy.
      # This includes the NumPy headers when compiling.
      include_dirs = [get_include()],
      ext_modules = ext_modules)

source_file.pyx

cdef extern from "c_penjumlahan.h":
	void c_penjumlahan(double* a, double* b, double* c)

cdef extern from "c_perkalian.h":
	void c_perkalian(double* a, double* b, double* c)

def penjumlahan(double a, double b):
	cdef:
		double c
	c_penjumlahan(&a, &b, &c)
	return c

def perkalian(double a, double b):
	cdef:
		double c
	c_perkalian(&a, &b, &c)
	return c

How to run setup.py

python setup.py build_ext -inplace --plat-name=win-amd64
python setup.py install

Requirements for Windows:

1. minGW-w64 (download)
2. (optional case) if this statement is out on cmd error: Unable to find vcvarsall.bat then the computer need to install Visual Studio (download). During the installation, select the Python development workload and the Native development tools option.

Personal:
Python version: 3.8.10
Conda version: 4.9.2
OS: Windows 10 Pro ver. 10.0.19042 Build 19042

The Example

(base) C:\go\to\directory>python
>>> import kalkulator
>>> kalkulator.penjumlahan(3,5)
8.0
>>> kalkulator.perkalian(3,5)
15.0