_normalize_keyword_aggregation` named agg helper function should be made public

[arpit1997]

Slightly related to #28380

Currently an issue in Dask dask/dask#5294 for implementing Named Aggregation (introduced in pandas 0.25.0) is open. To implement this it needs to use _normalize_keyword_aggregation and _is_multi_agg_with_relabel.

Making it public would be useful for frameworks like dask mars

cc: @TomAugspurger

[TomAugspurger]

And as an alternative to making it part of the official public API for end-users, we could add a test to ensuring that it's implementation doesn't move, so that projects like dask can rely on it.

That last option conflicts a bit our desire to deprecate all of pandas.core though.

[zbrookle]

@TomAugspurger Could I work on this? I'm interested in seeing this moved forward since I need the named aggregation feature in Dask to incorporate it into the dataframe_sql framework that I'm building

[TomAugspurger]

That sounds good.

…

On Sun, May 17, 2020 at 6:19 PM Zach Brookler ***@***.***> wrote: @TomAugspurger <https://github.com/TomAugspurger> Could I work on this? I'm interested in seeing this moved forward since I need the named aggregation feature in Dask to incorporate it into the dataframe_sql framework that I'm building — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#28472 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAKAOIS2VOYLST3FEMDIN4DRSBWH3ANCNFSM4IXHWEBQ> .

[jbrockmendel]

@rhshadrach these now live in core.apply, so im declaring this your call.

[rhshadrach]

The linked issue is now closed, with dask implementing it using reconstruct_func (which calls normalize_keyword_aggregation). With this, I'm okay with considering reconstruct_func public and adding tests, but I don't think we should adding it to the API.

cc @mroeschke for any thoughts.

[jbrockmendel]

+1 for something pseudo-public

[mroeschke]

+1 as well for exposing this publicly somehow

[rhshadrach]

What would be the reason for moving them?

[renatocmaciel]

The only path that explicitly mentions pseudo-public api is internals.
reconstruct_func , is_multi_agg_with_relabel and normalize_keyword_aggregation are accessible as they do not start with _ or __.

What are your thoughts on this issue? Should they be documented and made available on pandas/core/api.py or we only need to add tests?

[rhshadrach]

This is not widely know, but the API documentation (https://pandas.pydata.org/pandas-docs/dev/reference/index.html) states:

The pandas.core, pandas.compat, and pandas.util top-level modules are PRIVATE. Stable functionality in such modules is not guaranteed.

As such, to ensure we don't accidentally break dask, I think it would be sufficient to add a test for just reconstruct_func within pandas/tests/apply with a comment to the effect of "Test is to ensure this method isn't moved; it is used by other libraries (e.g. dask)"