Introduction of pyecrad

[SebastienRietteMTO]

This PR aims at introducing a python wrapper around ecrad.

[FussyDuck]

All committers have signed the CLA.

[SebastienRietteMTO]

The python package can be installed in two ways:

• by entering pip install . in the ecrad root directory
• using the wheel from pypi test: pip3 install -i https://test.pypi.org/simple/ pyecrad --extra-index-url https://pypi.org/simple/

The wheels are built and pushed on pypi by ./pyecrad_wheel.sh all pyecrad (provided that a pyecrad entry exists in ~/.pypirc)

A simple test can be performed with cd practical; python3 -c "import pyecrad; ecrad=pyecrad.Ecrad('config.nam').driver('era5slice.nc', 'output_py.nc')". This will create the output_py.nc which must be equivalent to the file obtained with ../bin/ecrad config.nam era5slice.nc outpu_ori.nc.

[reuterbal]

Many thanks for this, that looks very interesting. I would like to give that a proper round of testing before I will be able to make more substantial remarks on the implementation. In the meantime, I'm flagging already a few things that would help the integration:

• Would you mind adding a README to the pyecrad directory to explain the purpose and use?
• Can you please add licence headers to the script and Python files? Take a look at the equivalent headers in other files for this.
• We will need a build system integration into CMake as well. We have templates for this e.g. in https://github.com/ecmwf-ifs/ifsbench and https://github.com/ecmwf-ifs/loki that we can adapt here. I can help with that.
• I would like to add the definition of some CTest tests (e.g. via pytest) to ensure this remains functional going forward, e.g., by comparing the produced output against the equivalent output of CTest runs of the pure Fortran binaries. Again, I can help with that.
• The compare.py script serves the same purpose as the existing nccmp.py script, could the latter be used instead of duplicating the functionality?

I hope that makes sense and happy to help with the above where required.

[SebastienRietteMTO]

@reuterbal I did the easiest part (README, license, and removal of compare.py), but I'm not sure how to address your other two comments, especially since I'm not an expert in cmake/ecbuild. I did add a script that can be discovered by pytest, but it's not included in CMakeLists.txt.