f2py: Running Fortran code in Python on Windows, Linux, and Mac

f2py allows importing unmodified Fortran code as a library/module. If the existing Fortran code does not specify “intents”, you can add !f2py intent() comments instead of actual code.

Here is a simple example of correctly specifying Fortran Intent() vis-à-vis Python f2py to consider for Fortran->Python projects.

Install f2py

f2py is part of numpy, so we install Numpy.

Linux / Windows Subsystem for Linux

apt install gfortran
conda install numpy

Mac OS

brew install gcc
conda install numpy

Windows

Alternative: Windows Subsystem for Linux.

Tested on a 64-bit Windows 10 machine.

  1. install Numpy

     conda install numpy
    
  2. install MinGW-W64 to c:\mingw with the setup settings:

    Architecture Threads Exception
    x86_64 posix seh
  3. Insert the mingw bin path to your system path permanently: Control Panel > Advanced System Settings > Environment Variables > System variables > Path. Add the path to gfortran.exe, such as:

     C:\mingw\mingw64\bin
    
  4. Tell Python to use MinGW: create file c:\Anaconda\Lib\distutils\distutils.cfg containing:

     [build]
     compiler=mingw32
    

Test/fix your f2py installation

Try the lowtran7 code. Following the instructions there, you should get

  1. A lowtran7.pyd (on Windows) or lowtran7*.so (on Linux) file
  2. Running python DemoLowtran.py creates a plot of atmospheric loss
Lowtran atmospheric loss line plot
Lowtran atmospheric loss.

f2py does not allow inline comments for COMMON blocks

f2py does not allow inline comments for COMMON blocks for Fortran 77 .f code. This is because f2py works more strictly to Fortran specifications than most modern compilers.

Inline comments are not Fortran 77 standard, and will make f2py throw an error.

To fix this problem, just make the inline comment a full-line command with ! in column 1.

Fortran90 .f90 files won’t throw an f2py error due to inline comments on a line with a COMMON block.

This will manifest itself two different ways, depending on whether you have implicit none or not:

COMMON inline comment error WITH implicit none

Example in badcomment_implicit.f

var2fixfortran: No typespec for argument “x ! bad for fortran77”. getctype: No C-type found in “{}”, assuming void. KeyError: ‘void’

Solution: Make inline comment a full-line comment with ! in column 1.

COMMON inline comment error WITHOUT implicit none

Example in badcomment.f

error: expected ‘;’, ‘,’ or ‘)’ before ‘!’ token

Solution: Make inline comment a full-line comment with ! in column 1.

Windows: troubleshooting f2py errors

Another solution is to use Windows Subsystem for Linux with Anaconda Python. However, with the techniques below, I’ve always gotten f2py to work on Windows 7 and Windows 10.

‘f2py’ is not recognized as an internal or external command, operable program or batch file.

  1. Ensure Numpy is installed

     conda install numpy
    
  2. (Windows) create a file <Anaconda Python install directory>/Scripts/f2py.bat with content

     python %~dp0/f2py.py %*
    

Error: No module named ‘numpy.distutils._msvccompiler’ in numpy.distutils; trying from distutils

is fixed by: create file c:\Anaconda\Lib\distutils\distutils.cfg containing:

    [build]
    compiler=mingw32

Previously fixed Windows f2py bugs

I previously published these bug fixes, now incorporated into Numpy releases.

Error: ValueError: Unknown MS Compiler version 1900`

This is fixed in Numpy 1.13.1

  1. manually patch the file <Anaconda Python install directory>/Lib/distutils/cygwinccompiler.py on line 157 and line 318, replacing

     #self.dll_libraries = get_msvcr()
    

    with the word

     pass
    
  2. manually patch the file <Anaconda Python install directory>/Lib/site-packages/numpy/distutils/mingw32compiler.py, commenting out lines 96-104

     # Check for custom msvc runtime library on Windows. Build if it doesn't exist.
     #msvcr_success = build_msvcr_library()
     #msvcr_dbg_success = build_msvcr_library(debug=True)
     #if msvcr_success or msvcr_dbg_success:
         # add preprocessor statement for using customized msvcr lib
     #    self.define_macro('NPY_MINGW_USE_CUSTOM_MSVCR')
    
     # Define the MSVC version as hint for MinGW
     #msvcr_version = '0x%03i0' % int(msvc_runtime_library().lstrip('msvcr'))
     #self.define_macro('__MSVCRT_VERSION__', msvcr_version)
    

References

Reference

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