Optional extras to manage dependencies

It would help if xarray provided a bunch of optional extras to manage the dependencies when it’s installed, e.g. xarray['netcdf4'] etc etc; it’s not sufficient to simply list a few things on http://xarray.pydata.org/en/stable/installing.html because that provides no guidance or management for compatible versions. Since some dependencies like Pandas are still at 0.x versions that can and will break APIs, it’s important to have this version guidance and management (including relevant test suites).

[dazza-codes]

Since xarray is operating as a meta-package with various wrappers, it is the only place that can apply version compatibility on it’s dependencies. If there are optional dependencies, the python package extras are the process to manage them (not a README). The SEM-VER standards allow specification of more than one version for any dependency (so long as it complies with SEM-VER standards).

Essentially, this is a request for more sophistication in the setup.py file

• https://github.com/pydata/xarray/blob/master/setup.py

Consider, for example, how Apache Airflow does it:

• https://github.com/apache/airflow/blob/master/setup.py
• https://github.com/apache/airflow/blob/master/setup.py#L353

[equaeghe]

Even if version information is (not yet) available, this would be very useful. Currently, when packaging xarray for downstream distributions, it is a very burdensome task to piece together which optional dependencies there are in the first place. I understand that dealing with the backlog makes this a rather tedious task, but making it a requirement going forward to add such dependency information whenever a dependency is changed or added would be required in any case.