ENH: Have Period/PeriodIndex inherit from Interval/IntervalIndex

[jschendel]

Since Period objects are inherently intervals of time, it seems like there should be a way to access Interval properties and methods. Inheritance has been suggested in passing in other issues, and seems reasonable.

As an example benefit, #9089 suggests implementing Period.duration. If Period were to inherit from Interval, this would already be implemented via the Interval.length property:

In [2]: p = pd.Period('2018Q1', freq='Q')

In [3]: p_iv = pd.Interval(p.start_time, (p + 1).start_time, closed='left')

In [4]: str(p_iv)
Out[4]: '[2018-01-01, 2018-04-01)'

In [5]: p_iv.length
Out[5]: Timedelta('90 days 00:00:00')

Likewise for PeriodIndex inheriting from IntervalIndex. Would be nice to have cross compatibility between the two, e.g. IntervalIndex.overlaps(Period) or PeriodIndex.get_loc(Interval).

[jreback]

there is an existing issue about making Period inherit from Interval (and same with PI and II)

it might not be bad

[jschendel]

@jreback : I recall seeing that mentioned somewhere, but can't find a corresponding issue. Do you happen to know where it is?

Also, would adding this method still be worthwhile if inheritance is implemented? Maybe if someone wanted to add a non-compatible Interval to a PeriodIndex, they'd need convert to IntervalIndex first? Not sure how common/useful that would be. Might just close this if there's no clear benefit to having this in addition to inheritance.

[jreback]

i couldn’t find the issue but iirc some disscussiom on the II original issue maybe

yeah inheritance would be nice here

can repurpose this issue

[jbrockmendel]

After some thought, I'm -1 on this. Assuming the Interval in question would have endpoints that are themselves Timestamps, this would limit the range of Period/PeriodIndex to the same bounds as Timestamp. Representing distant-past/future times is a use case that right now can only be done with Periods.

[jbrockmendel]

Closing based on the argument above. Feel free to re-open for further discussion.