pandas Calendar issue

January 1, 2022

This code for CustomBusinessDay() works fine:

from datetime import datetime
from pandas.tseries.offsets import CustomBusinessDay

runday = datetime(2021,12,30).date()
nextday = (runday + CustomBusinessDay()).date()

output 1:

In [26]: nextday
Out[26]: datetime.date(2021, 12, 31)

However, when adding an optional calendar as in date functionality , it produces the next business day even though today’s date (Dec 31, 2021) is not a holiday according to a specified calendar below:

from pandas.tseries.holiday import AbstractHolidayCalendar, Holiday, \
    USMemorialDay,  USMartinLutherKingJr, USPresidentsDay, GoodFriday, \
    USLaborDay, USThanksgivingDay, nearest_workday


class NYSECalendar(AbstractHolidayCalendar):
    ''' NYSE holiday calendar via pandas '''
    rules = [
        Holiday('New Years Day', month=1, day=1, observance=nearest_workday),
        USMartinLutherKingJr,
        USPresidentsDay,
        GoodFriday,
        USMemorialDay,
        Holiday('USIndependenceDay', month=7, day=4, observance=nearest_workday),
        USLaborDay,
        USThanksgivingDay,
        Holiday('Christmas', month=12, day=25, observance=nearest_workday),
        ]
nextday = (runday + CustomBusinessDay(calendar=NYSECalendar())).date()

output2:

In [27]: nextday
Out[27]: datetime.date(2022, 1, 3)

>Solution :

This line is the location of your problem:

Holiday('New Years Day', month=1, day=1, observance=nearest_workday)

If you take a look at the source code, nearest_workday means that the holiday is observed on a Friday if it falls on a Saturday, and on a Monday if the holiday falls on a Sunday. Since New Year’s Day 2022 falls on a Saturday, it is observed today (12/31/2021) according to your calendar.

Removing the observance parameter will lead to an output of 2021-12-31.