make "heavy" dependencies optional

[cehbrecht]

Currently eggshell has "heavy" dependencies which are required, for example:

• matplotlib
• cartopy
• ocgis

To make eggshell usable also for lightweight birds (wps services) we could make those dependencies optional ... functionality using these libraries is only loaded/available when the libraries are installed (ocgis, matplotlib, ...).

[huard]

I could move those utilities into subpackages. They won't be imported by import eggshell.

Does that mean creating an environment-dev.yml file with those optional dependencies ?

[huard]

Also, I suppose this means that the real birds have the responsibility of having those dependencies, and not delegate non-trivial dependencies to eggshell.

[cehbrecht]

The environment.yml is used for development and we can keep all conda dependencies here, just adding a comment for optional packages. But we should split the requirements.txt which is used by the Python package. Maybe having something like requirements-opt.txt? -dev is already used for the test requirements pytest etc.

Also, I suppose this means that the real birds have the responsibility of having those dependencies ..

yes.