Examples of using f2py to get high-speed Fortran integrated with Python easily

f2py Examples

Simple examples of using f2py to get high-speed Fortran integrated with Python easily.
These examples are also useful to troubleshoot problems with f2py.

Build

Fortran compiler is needed:

Mac: brew install gcc
Linux: apt install gfortran or yum install gfortran
Windows

Install

pip install -e .

This will compile the Fortran code (in .f and .f90 files).
It creates a file pyprod.* where * depends on operating system and Python version:

Linux/Mac: .so
Windows: .pyd

Examples

.f2py_f2cmap required

A file .f2py_f2cmap as in this repository must be in the top-level (same as setup.py) of the project directory tree.
If this file is missing, all "real" kinds map to float32, which is not in general what is wanted.
A missing .f2py_f2cmap will lead float64 values to be completely incorrect.

The names in the .f2py_f2cmap must exactly match the Fortran variable names used for the real kind.
If you use dp=>real64 in the Fortran code, then .f2py_f2cmap must map dp as well.

Fortran Intents

python f2py_demo.py

output:

x = 3
y = 2
x * y = 6.0
Your system did this in Python using Fortran-compiled library

Fortran comment syntax

Fortran 77 is officially full-line comments only. Inline comments are
not allowed with f2py as a result in Fortran 77 files. Demonstrate
this with:

f2py -m badcomment -c badcomment.f

Troubleshooting f2py

f2py normally Just Works on Linux, MacOS and
Windows Subsystem for Linux.
However, Windows itself can be more challenging due to inconsistencies in Microsoft Visual Studio.

See the Windows f2py installation guide and troubleshooting
guide.