[Python] Pandas is_year_end

I am using Python 3.11.3 on Windows and Pandas 2.0.0.

I have this code with

from datetime import datetime
import pandas as pd

pd.__version__
'2.0.0'

rng = pd.date_range(start='2017-01-01', end='2018-01-01', freq='B')

rng[-10:]

DatetimeIndex(['2017-12-19', '2017-12-20', '2017-12-21', '2017-12-22',
'2017-12-25', '2017-12-26', '2017-12-27', '2017-12-28',
'2017-12-29', '2018-01-01'],
dtype='datetime64[ns]', freq='B')

rng[-10:].is_year_end

array([False, False, False, False, False, False, False, False, True,
False])

rng[rng.is_year_end]

DatetimeIndex(['2017-12-29'], dtype='datetime64[ns]', freq='B')


While it is true that '2017-12-29' was the last business day of the year, it was not the last day of the year.

However,

rng2 = pd.date_range(start='2017-01-01', end='2018-01-01')

rng2[-10:]

DatetimeIndex(['2017-12-23', '2017-12-24', '2017-12-25', '2017-12-26',
'2017-12-27', '2017-12-28', '2017-12-29', '2017-12-30',
'2017-12-31', '2018-01-01'],
dtype='datetime64[ns]', freq='D')

rng2[-10:].is_year_end

array([False, False, False, False, False, False, False, False, True,
False])

rng2[rng2.is_year_end]

DatetimeIndex(['2017-12-31'], dtype='datetime64[ns]', freq='D')


Which makes more sense to me.

The documentation on pandas.DatetimeIndex.is_year_end or pandas.Series.dt.is_year_end does not specify anything about business days or any other constraint.

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