Summary

For historic reasons, Scales take the axis as the first parameter. It's use is discouraged and none of our own scales actually use it at least since #12831.

To simplify our code, we should get rid of that parameter.

Proposed fix

Do we know whether

• downstream libraries add their own Scales via register_scale()?
• user will directly instantiate our own Scale classes?

If so we need the full deprecation machinery:

1. Make scale_factory work with scales have or have not an initial axis parameter. Either by try-except with/without this parameter or by introspecting the signature.
   • MNT: Registered 3rd party scales do not need an axis parameter anymore #29358
2. Introspect scale classes passed to register_scale and warn if they still have the axis argument.
   • MNT: Registered 3rd party scales do not need an axis parameter anymore #29358
3. Make all our scales work with/without the axis parameter by adding a suitable decorator to their init functions. - Refactoring: Removing axis parameter from scales #29988
   Otherwise, we can simplify the transition.

--

Edit: Both questions are yes, so we need the full deprecation mechanism.