Adapt pysteps to allow for nowcast plugins.

[Loickemajou]

Creating a DGMR plugin to be intergrated into the pysteps nowcasts methods.

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Codecov Report

:x: Patch coverage is 81.39535% with 8 lines in your changes missing coverage. Please review. :white_check_mark: Project coverage is 83.99%. Comparing base (917c83b) to head (45070d4). :warning: Report is 43 commits behind head on master.

Files with missing lines	Patch %	Lines
pysteps/nowcasts/interface.py	78.37%	8 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #418      +/-   ##
==========================================
+ Coverage   83.88%   83.99%   +0.10%     
==========================================
  Files         160      160              
  Lines       12780    12924     +144     
==========================================
+ Hits        10720    10855     +135     
- Misses       2060     2069       +9     

Flag	Coverage Δ
unit_tests	83.99% <81.39%> (+0.10%)	:arrow_up:

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[Loickemajou]

apologies for the slow action on this, I left few comments to clarify certain parts, but otherwise this is looking good!

So the actual plugin would be https://github.com/pySTEPS/pysteps-dgmr-nowcasts right? is everything ready on that side?

Hello @dnerini , thanks for reviewing the code.

Concerning the plugin, everything is ok, just left to include a test for the plugin.

[ladc]

I think this can soon be merged, although it shows that the current way the plugins are structured is hitting its limits. It leads to a lot of duplicate code and maintainability issues, and also it's not so flexible. I'll open a separate issue about that.

These modifications allow the pysteps-nowcast-dgmr plugin and other future nowcast plugins to be detected if installed.

[dnerini]

I think this can soon be merged, although it shows that the current way the plugins are structured is hitting its limits. It leads to a lot of duplicate code and maintainability issues, and also it's not so flexible. I'll open a separate issue about that.

Hi @ladc, could you please elaborate on the issues that you mentioned? anything we can do to improve it or should we rather go ahead with this PR as it is now and improve it in a separate effort?

[ladc]

I think the current state is fine, it enables nowcast plugins in pysteps, opening the door for all kinds of data driven methods. The reason why I said it's hitting its limits is because another internship student, @viktor40, wanted to create a plugin which included both post-processing and visualisation functionality, but the way the plugin system is currently designed only allows a single functionality type to be added. I suppose it's not too difficult to extend it but currently the internships are mostly finished so we'll have to do that at a later time. I would also need to add a test for the nowcast loader, but for that we need to update the cookiecutter - so I propose to go ahead and merge this in, if it's ok for everyone.