Python调用Fortran的三种形式

function area_of_circle (r)  
! function result     
implicit none      
   ! dummy arguments        
   real :: area_of_circle   
   ! local variables 
   real :: r     
   real :: pi
   pi = 4 * atan (1.0)     
   area_of_circle = pi * r**2  
end function area_of_circle

function area_of_circle (r) result(a)
implicit none
   real :: a
   real :: r
   real :: pi
   pi = 4 * atan (1.0)
   a = pi * r**2
end

subroutine area_of_circle (r,a)
implicit none
   real, intent(out) :: a
   real, intent(in) :: r
   real :: pi
   pi = 4 * atan (1.0)
   a = pi * r**2
end

python -m numpy.f2py -c circle.f90 -m circle

import circle
print(circle.__doc__)
print(circle.area_of_circle(2))

function area_of_circle(r) result(area) bind(c, name='area_of_circle')
    use iso_c_binding
    implicit none
    real(c_double) :: area
    real(c_double), intent(in) :: r
    real :: pi
    pi = 4 * atan (1.0)
    area = pi * r**2
end function area_of_circle

 gfortran -shared circle2.f90 -o circle2.so

import ctypes as ct

# import the shared library
fortlib = ct.CDLL('./circle2.so')

# Specify arguments and result types
fortlib.area_of_circle.argtypes = [ct.POINTER(ct.c_double)]
fortlib.area_of_circle.restype = ct.c_double

# Create a double and pass it to Fotran (by reference)
a = ct.c_double(2)
b = fortlib.area_of_circle(ct.byref(a))
print(b)

program calling_func
   real :: a
   a = area_of_circle(2.0)
   Print *, "The area of a circle with radius 2.0 is"
   Print *, a
end program calling_func

function area_of_circle(r)
! function result
implicit none
   ! dummy arguments
   real :: area_of_circle
   ! local variables
   real :: r
   real :: pi
   pi = 4 * atan (1.0)
   area_of_circle = pi * r**2
end function area_of_circle

import os
#编译
os.system(r"gfortran  ./circle3.f90 -o circle")
#调用编译的circle程序
os.system('./circle')