making python and fortran friends

f2py, fortran, python

Solution

I think you just need to change your f2py function signature slightly (so that `out_x` is only `intent(out)` and `in_x` is only `intent(in)`):

subroutine pow2(in_x, out_x)
  implicit none
  real, intent(in)   :: in_x
  !f2py real, intent(in) :: in_x
  real, intent(out)     :: out_x
  !f2py real, intent(out) :: out_x
  out_x = in_x ** 2
  return
end subroutine pow2

Now compile:

f2py -m test -c test.f90

Now run:

>>> import test
>>> test.pow2(3)   #only need to pass intent(in) parameters :-)
9.0
>>>

Note that in this case, `f2py` is able to correctly scan the signature of the function without the special `!f2py` comments:

!test2.f90
subroutine pow2(in_x, out_x)
  implicit none
  real, intent(in)   :: in_x
  real, intent(out)     :: out_x
  out_x = in_x ** 2
  return
end subroutine pow2

Compile:

f2py -m test2 -c test2.f90

run:

>>> import test2
>>> test2.pow2(3)   #only need to pass intent(in) parameters :-)
9.0
>>>

Problem

Assume we need to call fortran function, which returns some values, in python program. I found out that rewriting fortran code in such way: ``` subroutine pow2(in_x, out_x) implicit none real, intent(in) :: in_x !f2py real, intent(in, out) :: out_x real, intent(out) :: out_x out_x = in_x ** 2 return end ``` and calling it in python in such way: ``` import modulename a = 2.0 b = 0.0 b = modulename.pow2(a, b) ``` gives us working result. Can I call fortran function in other way, cause I think the first way is a bit clumsy?

Original source