BUG Fix: Series.add(DataFrame) fails to align
- [ ] closes #46179
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- [ ] Added an entry in the latest `doc/source/whatsnew/vX.X.X.rst` file if fixing a bug or adding a new feature.

> Not sure, if this should work. The docstring says Series or scalar. Can you check how this is annotated?

agreed. The error message should perhaps be more informative.

Seems to be a long-standing behavior. would probably need to check for similar issues or other examples which would suggest that this should work. I'm not sure we guarantee associativity for addition of these mixed classes. Also the flex methods are also for methods that are not associative so may need also to parametrize the test over all the flex methods if doing this change. As I assume from the issue, that's the reasoning for expecting `Series.add(DataFrame)` to work?

The docstring defines our public api, so also this would perhaps be an enhancement and not a bug.

I think we should also maybe push the discussion on expected behavior back to the issue.
 Agreed, let's continue the discussion to the issue before moving forward with the PR. Thanks @weikhor but feel free to contribute thoughts to the issue, closing for now.  @simonjayhawkins @mroeschke @phofl  Thank :)