DEPR: deprecate importing ErfaError and ErfaWarning from astropy.utils.exceptions

[neutrinoceros]

Description

Follow up to #10329, and in response to #13821 (comment)

This feels a bit too easy, so perhaps I'm missing something ? I'm considering that maybe it wasn't done 3 years ago because PEP 562 wasn't usable yet. This reasoning seems plausible since #10329 went into astropy 4.1, which was the last version to support Python 3.6 (PEP 562 landed in 3.7)

ping @mhvk

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[github-actions]

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[github-actions]

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[mhvk]

I think you are right that it is simply that module-level __getattr__ didn't exist yet - it is a very nice addition!
Just one comment with a further simplification in-line.

[mhvk]

I think this can just be

import erfa
return getattr(erfa, name)

[neutrinoceros]

thank you ! I was initially going to use importlib to do this dynamically but thought a dumb implementation was just as good, I missed that I could use getattr (ironic given that I was implementing __getattr__...)

[eerovaher]

Why not say in the change log entry where the error and warning should be imported from?

[neutrinoceros]

done !

[mhvk]

Happy that worked, and good addition to the changelog entry.

[mhvk]

p.s. Be sure to mention your improvements in #13821 - I like your approach of just removing minor pain points so we can avoid more major refactoring (or make it easier).

[mhvk]

Ah, I see you already did add a note in #13821 (comment) - thanks!

[MridulS]

It's usually recommended to atleast use stacklevel=2 in these warnings (ref python/cpython#88462)

[neutrinoceros]

True, but in the context of a module level __getattr__, and from my quick experiments, it doesn't seem to make any difference.

[mhvk]

I think this is OK as is, so will merge now. Thanks, @neutrinoceros!

[pllim]

@mhvk , please don't forget the milestone next time. I have added it here.