Chardata first working on feature branch

[pp-mo]

Successor to #6898
Now targetting (new) FEATURE_chardata feature branch in main repo

TODO: please check that any remaining unresolved issues on #6898 are now resolved here

[ukmo-ccbunney]

Looking pretty good. 👍🏼
I've got a few comments, questions and suggestions.

I have not looked at the tests yet - just the main Iris code. I thought it was worth submitting the review at this point so you can see the comments. I'll take a look at the tests next.

Also - remind me - what are we doing in the case where data is stored as a netCDF string type - i.e. the variable length string type? At the moment that just loads in as an object array in numpy. Were we just leaving that as-is? We can't write that kind of datatype in Iris.

Edit: Discussed with @pp-mo and he reminded me that we never intended to handle the variable length string cases.

[codecov]

Codecov Report

❌ Patch coverage is 92.92308% with 23 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.18%. Comparing base (043b0bc) to head (570eeb6).
⚠️ Report is 1 commits behind head on FEATURE_chardata.

Files with missing lines	Patch %	Lines
...ib/iris/fileformats/netcdf/_bytecoding_datasets.py	93.36%	9 Missing and 4 partials ⚠️
lib/iris/fileformats/netcdf/saver.py	91.95%	5 Missing and 2 partials ⚠️
lib/iris/fileformats/netcdf/_thread_safe_nc.py	81.25%	3 Missing ⚠️

Additional details and impacted files

@@                 Coverage Diff                  @@
##           FEATURE_chardata    #6975      +/-   ##
====================================================
+ Coverage             90.11%   90.18%   +0.07%     
====================================================
  Files                    91       92       +1     
  Lines                 24912    25092     +180     
  Branches               4675     4689      +14     
====================================================
+ Hits                  22449    22629     +180     
- Misses                 1684     1688       +4     
+ Partials                779      775       -4     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[ukmo-ccbunney]

Tests looks sensible as far as I can tell, with the expectation that there will be more coverage added as part of #6898.

[ukmo-ccbunney]

Nearly there, I think.
There is just your decision on this comment and a failing doctest/docs build to address.

Edit: The docs failures might be a transient error - seems to be related to a link failure in the InterSphinx links:

intersphinx inventory 'https://pandas.pydata.org/docs/objects.inv' not fetchable due to <class 'requests.exceptions.HTTPError'>: 522 Server Error: <none> for url: https://pandas.pydata.org/docs/objects.inv

https://pandas.pydata.org seems to be unresponsive at the time of wtriting.

[ukmo-ccbunney]

I think this is looking good now, as far as banking these changes in the feature branch go.
Well done @pp-mo 👍🏼 - this is definitely a thornier area than I expected!