def_expiry.py

import calendar
import pandas as pd
from make_holidaycsv import get_holidays


def expiry(year):
    """

    :param year:
    :return: It fetch the expiry date in list format for each month
    for year specified

    """

    df_holidays = get_holidays()

    df_holidays['tradingDate'] = pd.to_datetime(df_holidays['tradingDate'], format='%d-%b-%Y').dt.strftime('%d-%m-%Y')
    holiday_list = df_holidays['tradingDate'].tolist()
    expiry_list = ['Empty']  # since list starts from 0 this is a hacky way to align expiry_list[1] = first month

    for n in range(1, 13):
        month = n
        last_day = calendar.monthrange(year, month)[1]
        day_month = calendar.weekday(year, month, last_day)  # 0 is monday and 3 is Thu
        week = [3, 4, 5, 6, 0, 1, 2]
        days = -1

        for i in week:
            days += 1
            if i == day_month:
                break

        date_thu = last_day - days
        """
            zfill function formats single digits to double digits by adding a leading zero which is needed in 
            NSE option url
        """
        month_1 = str(month).zfill(2)
        date_1 = str(date_thu).zfill(2)
        expiry = (date_1) + "-" + (month_1) + "-" + str(year)

        "check if last Thu of the month (expiry day) is not holiday, if it is holiday then shift the date by one to Wed"

        for h in holiday_list:
            if expiry == h:
                date2 = str(date_thu - 1).zfill(2)
                expiry = (date2) + "-" + (month_1) + "-" + str(year)
        # print(expiry)
        expiry_list.append(expiry)

    return expiry_list