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Thanks for this PR :)
Getting the tests to pass is a bit tricky since the API for pyam changed when they went from version 1.9.0 to 2.0.0 (as you might expect) and our code needs to satisfy both versions since we test on Python <= 3.9, which is not supported for pyam 2.0.0. So let me take a closer look, maybe we'd want to use the function that pyam's sankey function wraps around directly, after all.

Thanks @daymontas1 for stepping up here, much appreciated :)

You should be able to test the PR as is and see how you like it's usefulness, but there are a few things that I would like to see happen before we merge it:

• Please rebase on main to keep it up to date with current developments.
• Please migrate the main functionality from util/__init__.py to somewhere more appropriate. E.g. report/sankey.py if it's a reporting tool or util/sankey.py if there are more general use cases.
• Please check if we can use plotly directly instead of pyam's wrapper functionality. This should allow us to utilize more design options and avoids some dependency constraints (see above). See some examples and their docs.
• Please confirm that we want to integrate the sankey functionality in the reporting as it currently stands. I'd probably ask at least @khaeru for his opinion.
• Please write a test if possible to confirm that sankey_mapper maps the correct values to the correct keys. We might also need to adapt one or two reporting tests that check the number of reporting steps if this stays in the default reporting workflow.

Please feel free to ask about any of these steps if you need help :)

Hi all, to simplify here, I would simply limit this functionality to pyam > 2 - we can do a version check for this on the fly and raise an error.

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.6%. Comparing base (ef66e37) to head (30d8d32).
Report is 20 commits behind head on main.

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##            main    #770     +/-   ##
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- Coverage   95.6%   95.6%   -0.1%     
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  Files         46      47      +1     
  Lines       4344    4383     +39     
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+ Hits        4154    4191     +37     
- Misses       190     192      +2