API: deprecate range-generating keywords in DatetimeIndex

[jorisvandenbossche]

I was reviewing the PR on the DatetimeIndex docstring, and the list of parameters is horribly complex because you can both use it by passing data (with accompanying keywords like copy, dtype, ..) and by generating a range with optional start, end, periods.

Since for generating ranges, we have the special purpose pandas.date_range, do we need to keep this functionality in the DatetimeIndex constructor as well?

Of course deprecating it will annoy people who use it (although I think the majority of usage of DatetimeIndex passed data), so the question is whether it is worth it.

[mroeschke]

+1. I'd be great to extend this to TimedeltaIndex and PeriodIndex as well.

[jreback]

yep should do this

[jorisvandenbossche]

We still need to do the same for PeriodIndex.

[TomAugspurger]

I'm working on this now. What's the plan for fields? I don't actually know what that does.

[TomAugspurger]

Hmm, slight API change (I think it counts as a bug) when start / end is a Period with a non-daily freq.

In [2]: start = pd.Period("2000", freq="B")

In [3]: pd.period_range(start, periods=4).freq
Out[3]: <Day>

In [4]: pd.PeriodIndex(start=start, periods=4).freq
Out[4]: <BusinessDay>

I think we want Out[4]. On master this is incorrect because the default value in period_range is 'D', not None.

[TomAugspurger]

On fields, I think that we should continue to accept them in the PeriodIndex constructor (at least, we shouldn't add them to period_range).