Using fortranmagic in IPython notebook for sorting an array: no return value

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I have to say that I am not a Fortran-programmer at all. I usually only use Python and C++, but sometimes colleagues have written great Fortran functions that would be great to implement in my Python code for efficiency. I was just about to try the f2py module via IPython's magic function.

For a trivial test, I have the following bubblesort implementation where I want to sort a Python list in place (which I convert to an numpy array laid out in memory the Fortran-style; I assume this would be more efficient than using Python lists right?)

However, the function has no return value here (None), and I am wondering where my mistake would be!?

The commands to install and load the fortranmagic which uses f2py

%install_ext http://ift.tt/1oIL7Nt
%load_ext fortranmagic

The Fortran bubblesort code:

%%fortran
SUBROUTINE fortran_bubblesort(a)
  REAL, INTENT(in out), DIMENSION(:) :: a
  REAL :: temp
  INTEGER :: i, j
  LOGICAL :: swapped = .TRUE.

  DO j = SIZE(a)-1, 1, -1
    swapped = .FALSE.
    DO i = 1, j
      IF (a(i) > a(i+1)) THEN
        temp = a(i)
        a(i) = a(i+1)
        a(i+1) = temp
        swapped = .TRUE.
      END IF
    END DO
    IF (.NOT. swapped) EXIT
  END DO
END SUBROUTINE fortran_bubblesort

The execution:

x = np.asfortranarray([3,2,1])
y = fortran_bubblesort(x)
print(x, y)

The result:

[3 2 1] None

asked 1 min ago

Sebastian Raschka

665