pyFMS

The pyFMS package is a Python-C-Fortran interface (through the use of the ctypes package), for access to select methods from the Flexible Modeling System (FMS) developed by NOAA/GFDL (https://github.com/NOAA-GFDL/FMS.git).

Quickstart - bare metal

Build

The build backend of pyFMS is scikit-build-core, which allows for the compilation of extension modules for Python packages through CMake.

pyFMS requires:

• GCC > 9.2
• MPI
• Python 3.12

To clone pyFMS from its GitHub repository:

git clone https://github.com/NOAA-GFDL/pyFMS.git

We recommend creating a Python venv or conda environment for your installation.

python -m venv <name_of_environment>
source .<name_of_environment>/bin/activate

Inside of your Python environment, to install pyFMS and its dependencies:

pip install .[install_options]

The available install_options are:

• test
• dev (which installs the test dependecies as well)
• extras (which installs the dev dependencies as well)

For developers we suggest installing with the editable flag -e and the verbose flag -v:

pip install -e -v .[dev]

use of the editable installation method will allow updates to the Python source code to be reflected in the installation without re-installing. Subsequent installs of pyFMS will recompile all extension modules, due to the methods of compilation used by scikit-build-core.

The CMakeLists.txt file will be accessed by the build backend during the installation to compile the necessary shared object file from the C-Fortran interface, cFMS, to be loaded by the ctypes package for use by pyFMS.

Editing the extension modules of pyFMS

If you require a different version of cFMS and/or its dependency FMS, depending on the use case, two methods of use are available:

1. Edit the CMakeLists.txt file to point to the repository containing your custom cFMS and/or FMS to install it alongside pyFMS through the methods outlined above
2. Perform a separate compilation of cFMS and/or FMS outside of the provided build tools and point to the desired shared object file when running pyfms.cfms.init(libpath=<path_to_shared_object_library>)

pyFMS as a dependency

This package can be treated like any Python package when used needed as a dependency; ensure it is defined as a dependency for your project, and import as usual. Subsequent installs of the dependent package will not trigger a recompilation of the extension modules of pyFMS, unless directly called to due so by a reinstall of pyFMS, as the dependency manager of the build backend for the dependent project will see the requirements of pyFMS are satisfied. If an editable version of pyFMS is needed for the dependent package, please use the method of editable install detailed above.