Passing Arrays from Python to Fortran (and back)

Question

Background:
My program currently assembles arrays in Python. These arrays are connected to a front-end UI and as such have interactive elements (i.e. user specified values in array elements). These arrays are then saved to .txt files (depending on their later use). The user must then leave the Python program and run a separate Fortran script which simulates a system based on the Python output files. While this only takes a couple of minutes at most, I would ideally like to automate the process without having to leave my Python UI.

Assemble Arrays (Python) -> Edit Arrays (Python) -> Export to File (Python)
-> Import File (Fortran) -> Run Simulation (Fortran) -> Export Results to File (Fortran)
-> Import File to UI, Display Graph (Python)

Question:
Is this possible? What are my options for automating this process? Can I completely remove the repeated export/import of files altogether?

Edit: I should also mention that the fortran script uses Lapack, I don't know if that makes a difference.

Vladimir F Героям слава · Accepted Answer · 2014-01-19 10:53:49Z

5

You do not have to pass arrays to Fortran code using text files. If you create an entry point to the Fortran code as a subroutine, you can pass all the numpy arrays using f2py. You should be aware of that if you added the f2py tag yourself. Just use any of the numerous tutorials, for example https://github.com/thehackerwithin/PyTrieste/wiki/F2Py or http://www.engr.ucsb.edu/~shell/che210d/f2py.pdf .

The way back is the same, the Fortran code just fills any of the intent(out) or intent(inout) arrays and variables with the results.

answered Jan 19, 2014 at 10:53

Vladimir F Героям слава

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2 Comments

Tim Whitcomb Over a year ago

This is definitely an awesome way to go - just treat the Python layer as a driver for the Fortran subroutine(s) doing the heavy computation. Additional bonus is that if you write your Fortran code correctly (i.e. Fortran 90 with intent statements, etc.) the wrapping is pretty much automatic and you don't have to change much.

MarkyD43 Over a year ago

Thanks for the input guys, I've got f2py working with my program, I do however have an intermittent bug, but I think that deserves a post of its own!

Raman Shah · Accepted Answer · 2014-01-19 22:12:12Z

2

I love the Python+Fortran stack. :)

When needing close communication between your Python front-end and Fortran engine, a good option is to use the subprocess module in Python. Instead of saving the arrays to a text file, you'll keep them as arrays. Then you'll execute the Fortran engine as a subprocess within the Python script. You'll pipe the Python arrays into the Fortran engine and then pipe the results out to display.

This solution will require changing the file I/O in both the Python and Fortran codes to writing and reading to/from a pipe (on the Python side) and from/to standard input and output (on the Fortran side), but in practice this isn't too much work.

Good luck!

answered Jan 19, 2014 at 22:12

Raman Shah

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