example for stackoverflow

# author: Bartlomiej "furas" Burek (https://blog.furas.pl)
# date: 2020.04.25
# https://stackoverflow.com/questions/61361457/repeating-the-pattern-of-numbers-thrice-in-a-month/

import datetime
import numpy as np
from datetime import timedelta

Holiday_List = [
    '2020-01-01',  # remove date to test 3 'NW'
    '2020-01-05',  # remove date to test 3 'NW'
    '2020-01-12',
    '2020-01-19',
    '2020-01-26',
    #'2020-01-13',  # add extra date to test `gap >= 9`
    #'2020-01-14',  # add extra date to test `gap >= 9`
    #'2020-01-15',  # add extra date to test `gap >= 9`
]

Start_date = datetime.datetime(year=2020, month=1, day=1)
end_date = datetime.datetime(year=2020, month=1, day=28)

delta = end_date - Start_date
print(delta)

hDay = "Holiday"
dummy = "NW"

# --- numpy array ---

arr = np.array([1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18], dtype=object)  #Assumed that the array length of is divisible by 3 every time

arr = np.split(arr, 3)   #spilts the array to three equal parts

for i in range(len(arr[0]), 9):  # CHANGED: add 3 'NW' instead of 2 'NW'
    arr = np.insert(arr, i, dummy, axis=1)  # fill remaining slots with dummy value(NW)

print("{}\t{}\t{}".format("Date", "Holiday", "Values"))

# ---

i = 0

for numbers in arr:

    gap = 0
    numbers_index = 0
    numbers_count = len(numbers) - 3 # count numbers without 3 `NW`

    while i < delta.days + 1:
        day = Start_date + timedelta(days=i)
        i += 1

        if day.strftime("%Y-%m-%d") in Holiday_List:
            print("{}\t{}\t{}".format(day.strftime("%d-%m-%Y"), 1, hDay))
            if numbers_index > 0: # don't count Holiday before displaying first number from list `data` (ie. '2020-01-01')
                gap += 1
        else:
            value = numbers[numbers_index]
            # always put number (!='NW') or put 'NW' when gap is too small (<9)
            if value != 'NW' or gap < 9:
                print("{}\t{}\t{}".format(day.strftime("%d-%m-%Y"), 0, value))
                numbers_index += 1
                gap += 1
            # IDEA: maybe it could use `else:` to put `NW` without adding `NW` to `arr`

        # exit loop if all numbers are displayed and gap is big enough
        if numbers_index >= numbers_count and gap >= 9:
            break