Feature/optional dependencies

[sandorkertesz]

Fixes #252

See docs at: https://earthkit-data--269.org.readthedocs.build/en/269/install.html

The optional Python dependencies are now controlled in setup.cfg.

By default when installed from PyPI we get a minimal version:

Optional dependencies can be installed as:

[sandorkertesz]

Some more questions:

• should we make "grib" or "netcdf" as an optional dependency?
• how should earthkit and earthkit-maps define earthkit-data as a dependency? Should they specify earthkit-data[all] ???
• how should the earthkit-data conda install behave?

[iainrussell]

Looks good to me! I see we mention eccodes twice as a dependency (generally, and for BUFR support). Is that because BUFR support might require a newer version? I'd say that since both instances of the eccodes dep currently require the same version, we could drop it as a separate dep for BUFR.

[sandorkertesz]

Looks good to me! I see we mention eccodes twice as a dependency (generally, and for BUFR support). Is that because BUFR support might require a newer version? I'd say that since both instances of the eccodes dep currently require the same version, we could drop it as a separate dep for BUFR.

Fixed now!

[iainrussell]

Great, I think we're ready to merge then. Nice work!

[sandorkertesz]

Great, I think we're ready to merge then. Nice work!

Thank you! What do you think about the questions above?

[iainrussell]

Some more questions:

Sorry, I did not notice those questions.

• should we make "grib" or "netcdf" as an optional dependency?

I think for now they should be always there, as they are 'core' data types that we support, and the dependencies are easy to install everywhere.

• how should earthkit and earthkit-maps define earthkit-data as a dependency? Should they specify earthkit-data[all] ???

Good question. Probably 'earthkit' should install all, and ek-maps should be more conservative, but this is a slightly different question from this specific PR. And it depends a bit on whether lacking the binary dependencies would cause an error during 'import earthkit.data' in the 'all' case.

• how should the earthkit-data conda install behave?

Probably it should use 'all', but this will not work (yet) in practice because we do not have all the binaries available on conda-forge (e.g. odc, fdb). Once we have our own conda channel up and running, we will be able to do this. So, we should just put all the dependencies that are available on conda-forge as dependencies of the conda-forge package.

[sandorkertesz]

• how should earthkit and earthkit-maps define earthkit-data as a dependency? Should they specify earthkit-data[all] ???

Good question. Probably 'earthkit' should install all, and ek-maps should be more conservative, but this is a slightly different question from this specific PR. And it depends a bit on whether lacking the binary dependencies would cause an error during 'import earthkit.data' in the 'all' case.

'import earthkit.data' should be fine even when the binary dependencies are missing. This PR is only addressing the Python dependencies.