PR Summary

Closes#21409,#21413 (which it replaces)

The original complaint was that

importmatplotlib.pyplotaspltfig,ax=plt.subplots()ax.set_position([0.2,0.2,0.5,0.5])ax2=ax.twinx()plt.show()

didn't properly position the twin. This will still be a problem with this PR, however

import matplotlib.pyplot as pltfig, ax = plt.subplots()ax2 = ax.twinx()ax.set_position([0.2,0.2,0.5,0.5])plt.show()

works fine (whereas it did not before). I think this is probably acceptable.

Why we can't make it more flexible is that_make_twin is different forAxesSubplot versusAxes objects.AxesSubplot twins take the SubplotSpec of the sibling, where asAxes twins are "located" with their sibling.

The root of the problem here, in my opinion, is that twins are "siblings" versus children. If the twin was a child, it would just follow its parent around, but that is not how the code base with a Grouper treats them, and hence its not possible to tell which is the parent after the axes have been created.

PR Checklist

Tests and Styling

• Has pytest style unit tests (andpytest passes).
• IsFlake 8 compliant (installflake8-docstrings and runflake8 --docstring-convention=all).

Documentation

• New features are documented, with examples if plot related.
• New features have an entry indoc/users/next_whats_new/ (follow instructions in README.rst there).
• API changes documented indoc/api/next_api_changes/ (follow instructions in README.rst there).
• Documentation is sphinx and numpydoc compliant (the docs shouldbuild without error).