Embedding Fortran in Python with f2py

Question

I need a script to recurse across a directory structure, extract numbers from files in the directories, then perform calculations on those numbers. I am using Python as the main language for the script, but wanted to use Fortran for the numerical computations. (I am more comfortable with Fortran and it is a better tool for numerical work)

I am trying to use f2py, but I keep getting strange errors. f2py is complaining about my variable declarations, trying to change character(*) to integer and appending ! onto my variable names when I have a comment immediately following the variable declaration.

The subroutine is too long to post here, but takes two arguments, an input file name and output file name. It opens the input file, reads the numbers, processes them, then writes to the output file. I intend to use the Python script to write the numerical file in each directory and call the Fortran subroutine on it.

I can try to post a smaller example with the same issues, but are there any common 'gotchas' with f2py? I am using gfortran v4.6.1, python v3.2.2, and f2py v2.

EDIT: Here is a small example with the same errors:

itimes-s.f (File containing subroutine to be used from python):

  module its

  contains

  subroutine itimes(infile,outfile)

    implicit none

    ! Constants
    integer, parameter :: dp = selected_real_kind(15)

    ! Subroutine Inputs
    character(*), intent(in) :: infile    ! input file name
    character(*), intent(in) :: outfile   ! output file name

    ! Internal variables
    real(dp) :: num               ! number to read from file
    integer :: inu                ! input unit number
    integer :: outu               ! output unit number
    integer :: ios                ! IOSTAT for file read

    inu = 11
    outu = 22

    open(inu,file=infile,action='read')
    open(outu,file=outfile,action='write',access='append')

    do
      read(inu,*,IOSTAT=ios) num
      if (ios < 0) exit

      write(outu,*) num**2
    end do

  end subroutine itimes

  end module its

itests.f (Fortran driver program):

  program itests

  use its

  character(5) :: outfile
  character(5) :: infile

  outfile = 'b.txt'
  infile = 'a.txt'

  call itimes(infile, outfile)

  end program itests

a.txt:

1
2
3
4
5
6
7
8
9
10.2

b.txt after compiling and running itests and itimes-s using gfortran only:

   1.0000000000000000     
   4.0000000000000000     
   9.0000000000000000     
   16.000000000000000     
   25.000000000000000     
   36.000000000000000     
   49.000000000000000     
   64.000000000000000     
   81.000000000000000     
   104.03999999999999     

Running f2py using f2py.py -c -m its itimes-s.f produces numerous errors however. (not posted due to length, but if someone wants I can post them)

Answer 1

I have never tried using f2py to wrap a full Fortran module. However, if you extract the itimes function from the module into its own file and then run the same f2py command, everything appears to work when I tried it locally (f2py v2, numpy 1.6.1, python 2.7.2, gfortran 4.1.2).

Also, note that you are not explicitly closing your input and output files, though this has no real bearing on f2py's working or not.