API: Datetime-like indexes summary should output the same format

[sinhrks]

Related to #6469. Made all datetime-like indexes summary should output the same format.

Before

didx = pd.date_range('2014-12-20', freq='M', periods=3)
pidx = pd.period_range('2014-12-20', freq='M', periods=3)
tdidx = pd.timedelta_range(start='1 days', freq='D', periods=3)

didx.summary()
# DatetimeIndex: 3 entries, 2014-12-31 00:00:00 to 2015-02-28 00:00:00
# Freq: M

pidx.summary()
# PeriodIndex: 3 entries, 2014-12 to 2015-02

tdidx.summary()
# TimedeltaIndex: 3 entries, '1 days' to '3 days'
# Freq: <Day>

After

• DatetimeIndex and PeriodIndex use _format_func. This made DatetimeIndex not to output hour/minutes.. when its frequency is more than a day.
• PeriodIndex outputs its freq
• TimedeltaIndex has no changes.

# DatetimeIndex: 3 entries, 2014-12-31 to 2015-02-28
# Freq: M

# PeriodIndex: 3 entries, 2014-12 to 2015-02
# Freq: M

# TimedeltaIndex: 3 entries, '1 days' to '3 days'
# Freq: <Day>

[jreback]

somewhat separately the freq printing for TimeDeltaIndex is showing the actual obj and not the string repr

[sinhrks]

Yeah, TimedeltaIndex.freqstr is not compat with others. Can I fix this in the same PR, or shoudld be separate?

# DatetimeIndex
didx.freqstr
# M

# TimedeltaIndex
tdidx.freqstr
# <Day>

[jreback]

I think u can fix it here
it shouldn't break anything (if it gets too complicated do a separate one)

[jorisvandenbossche]

Can you now you are modifying it also add a docstring?

[sinhrks]

@jreback, @jorisvandenbossche
Updated, could you check?

[jorisvandenbossche]

Looks good to me!

[jreback]

thanks @sinhrks