API: Remove kwargs from GroupBy

[topper-123]

Remove kwargs from _GroupBy`.__init__ and adds an explicit mutated parameter name instead. Also makes related changes.

Avoiding kwargs when possible is better for typing ergonomics.

[topper-123]

I'm not sure what mutated actually does. It's tested for in window/test_grouper.py so assume it has something to do with windowing ops. anyone got a suggestion for a better doc string?

[jbrockmendel]

generally +1. im also unclear on the mutated thing. I epxect we dont want users passing it directly, wondering if it can be kept out of the top-level method signature

[topper-123]

wondering if it can be kept out of the top-level method signature.

It is already allowed in the top-level signature, it's just hidden, so it would have to go through a deprecation process. But else I agree.

[WillAyd]

I am actually -1 on this change; unfortunate that we accept kwargs here but mutated is entirely an internal construction. I don't think we should expose it out as part of the GroupBy API

[topper-123]

If mutated is internal, I think it should not be in the NDFrame.groupby signature, becuase that is a public signature. It should just call pandas.core.groupby.groupby.groupby directly, bypassing NDFrame.groupby.

[jreback]

this is changing a public API. The reason the kwargs was added was to work around some internal routines calling this. So I wouldn't do this; rather we can work on cleaning how this is called to avoid passing thru here.

[topper-123]

I've made a few changes:

• the mutated parameter in NDFrame.groupby has been formally deprecated.
• I've renamed grouper.groupby.groupby to grouper.grouper.get_groupby to better signal it's a function
• I've typed out the parameters of get_groupby to make its signature explicit.

It didn't seem that any internal functionality actually used mutated. At least no tests that don't explicitly use mutated failed.

[jreback]

why would you deprecate? it is not public

[jorisvandenbossche]

It didn't seem that any internal functionality actually used mutated. At least no tests that don't explicitly use mutated failed.

If this is correct, we could also directly remove it? (it has never been publicly exposed, only hidden in the kwargs, so I don't think a user could ever have known to pass a mutated keyword?)

[topper-123]

Ok, I've removed mutated from NDFrame.groupby.

[jreback]

thanks @topper-123 nice clean