support iris > 3.7

[jgriesfeller]

No description provided.

[jgriesfeller]

It looks like iris does not allow non CF compliant units anymore (since V3.7) I opened a discussion at the iris gihub site: SciTools/iris#5856

Let's see what they say.

[jgriesfeller]

looking at the saver code here:
https://github.com/SciTools/iris/blob/cbb08457fc139249ed89b1970eb326144a7074ec/lib/iris/fileformats/netcdf/saver.py#L1713-L1715
It really seems that we lost the abiliy to save netcdf files with cutom units
The loader part here:
https://github.com/SciTools/iris/blob/cbb08457fc139249ed89b1970eb326144a7074ec/lib/iris/fileformats/_nc_load_rules/helpers.py#L895-L920
does not look promising reagarding loading netcdf files with non CF units either.

[jgriesfeller]

Bad news from iris: One of the maintainers there said that he is surprised that using non CF units ever worked... Digging a bit deeper to see what really changed...

[jgriesfeller]

Things were not as bad as it seemed. As long as the cf_units package understands the the unit, we are still fine. Iris had just changed it's warnings if that was not the case.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.27%. Comparing base (5ff89df) to head (2e4ce15).

Additional details and impacted files

@@            Coverage Diff            @@
##           main-dev    #1061   +/-   ##
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  Coverage     79.27%   79.27%           
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  Files           109      109           
  Lines         19023    19023           
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  Hits          15080    15080           
  Misses         3943     3943           

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unittests	79.27% <ø> (ø)

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