Correctly re-instate Matplotlib converters

[dstansby]

Fixes #27479. Converters should only be cached to be re-instated if they are original, and not pandas converters.

I'm struggling to write a test for this; I think it requires a clean state with no pandas imports, so one can check what was in the units registry before pandas was imported. I think this means a new test file with no pandas imports at the top, but maybe someone has a better idea?

[TomAugspurger]

Thanks for this!

I'm struggling to write a test for this;

Testing these is quite hard (we accidentally broke the warning for a release and didn't notice).

pandas/pandas/tests/plotting/test_converter.py

Line 31 in 9bab81e

def test_initial_warning():

works reasonably well I think. The idea is to run the check in a subprocess.

[TomAugspurger]

A release note in whatsnew/0.25.1.rst would be nice to have. I think there's a "plotting" subsection.

[codecov]

Codecov Report

Merging #27481 into master will increase coverage by 49.17%.
The diff coverage is 100%.

@@             Coverage Diff             @@
##           master   #27481       +/-   ##
===========================================
+ Coverage   42.44%   91.62%   +49.17%     
===========================================
  Files         184      184               
  Lines       50389    50388        -1     
===========================================
+ Hits        21389    46167    +24778     
+ Misses      29000     4221    -24779

Flag	Coverage Δ
#multiple	91.62% <100%> (?)
#single	?

Impacted Files	Coverage Δ
pandas/plotting/_matplotlib/converter.py	63.64% <100%> (+49.94%)	⬆️
pandas/core/computation/pytables.py	63.71% <0%> (-26.22%)	⬇️
pandas/io/pytables.py	65.55% <0%> (-23.83%)	⬇️
pandas/io/clipboard/clipboards.py	31.88% <0%> (-2.9%)	⬇️
pandas/util/_test_decorators.py	93.84% <0%> (+4.61%)	⬆️
pandas/io/gbq.py	88.88% <0%> (+5.55%)	⬆️
pandas/_config/localization.py	86% <0%> (+6%)	⬆️
pandas/core/dtypes/inference.py	100% <0%> (+13.33%)	⬆️
pandas/compat/numpy/__init__.py	93.1% <0%> (+13.79%)	⬆️
pandas/core/config_init.py	96.2% <0%> (+13.92%)	⬆️
... and 138 more

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[dstansby]

Thanks for the test tip, the new test fails before the changes in this PR.

[jreback]

also pls merge master

[dstansby]

I'm away for the next week or so without a computer, so if anyone wants this in quicker than that feel free to force push to my branch.

[dstansby]

Is there anything else (apart from a rebase) I need to do on this?

[TomAugspurger]

Looks good. Ping on green.

[TomAugspurger]

Did you merge master before pushing? We've seen similar CI failures, but I thought we fixed them all on master.

[dstansby]

Yeah, I should have rebased on to master, I've done another rebase to see if that fixes the tests.

[TomAugspurger]

Merged master again to see if we can get the CI passing.

[TomAugspurger]

Thanks @dstansby. Sorry about the CI issues.