DEPR: Index.get_value ?

[jorisvandenbossche]

Index.get_value is a very strange (from user perspective), and completely undocumented method, so let's rename it to _get_value for internal usage and deprecate the public one?

Example usage to show its 'not-usefulness':

In [85]: idx = pd.Index([1, 2, 3])

In [87]: idx.get_value(np.array([0, 1, 2]), 2)
Out[87]: 1

(so you can index into another object based on the location of the key in the calling index)

[jreback]

iirc this is heavily used in indexing code
renaming just causes bloat - rather deprecation and fixing are better

[jorisvandenbossche]

But what needs to be fixed? If it is heavily used in indexing code, it is probably useful?
IMO, the only thing that needs to be fixed is the fact that it is a public method, and then simply renaming does the trick (indexing code can maybe use a refactor, but that's a totally different and much bigger issue)

[jreback]

no you are missing the point here. A lot of index methods are used internally to do indexing. But that does not necessarily mean they should be publicly exposed, though they are currently. If we are making first class extensions, then all methods should be public and pandas itself should not even internally rely on indexing methods (and if they do they would be private).

So its public now, deprecating the current function just causes one more method and that is just smelly. If you want to deprecate it, then it should be completely removed from the internal API and just call public methods).

[jorisvandenbossche]

I was not speaking about extensions here.
But about that, do you think there are Index subclasses in the wild that rely on get_value ?

[jorisvandenbossche]

Ah, yes, based on @shoyer 's comment here #15258, it's indeed needed at this moment to implement custom Index subclass.

[jreback]

I don't care if we have Index sub-classes in the wild. that's not my point. We should get rid of .get_value, but NOT by simply renaming it. It needs to be properly removed internally.

[shoyer]

I don't think there are Index subclasses in the wild that rely on get_value. There might be subclasses that implement get_value, but they should still work fine when it's removed.

[jorisvandenbossche]

There might be subclasses that implement get_value, but they should still work fine when it's removed.

@shoyer But if Series.__getitem__ now uses its index get_value, and we would rename / remove that, doesn't that mean that a Series with such a subclassed index would no longer work for those cases where it was used?

[shoyer]

If I recall correctly, index.get_value(series, key) is basically equivalent to series.iloc[index.get_loc(key)] (but it possibly faster). Assuming that the Index subclass implements get_loc (which is basically required for meaningful indexing) it should work fine with this fall-back.