Basic datetime implementation in Python

my_date_time.py

import time
import datetime

SECONDS_EVERY_FOUR_YEARS = (365 * 4 + 1) * 24 * 3600
SECONDS_EVERY_YEAR = 365 * 24 * 3600
SECONDS_EVERY_DAY = 24 * 3600
DAYS_EVERY_MONTH = [31, (28, 29), 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]
SECONDS_AFTER_FIRST_LEAP_YEAR = SECONDS_EVERY_YEAR * 3 + SECONDS_EVERY_DAY

def _get_numbers_of_days_the_month(m, years_since_last_leap_year):
    if m == 1: 
        if years_since_last_leap_year == 0:
            days_month = DAYS_EVERY_MONTH[1][1]
        else:
            days_month = DAYS_EVERY_MONTH[1][0]
    else:
        days_month = DAYS_EVERY_MONTH[m]
    return days_month

def _calculate_first_days():
    current_value = 2 # December 1st 1971 was a Wednesday
    for y in range(0, 28):
        year_count = y % 4
        for m in range(0, 12):
            previous_month = m - 1 % 12
            days_of_the_month = _get_numbers_of_days_the_month(previous_month, year_count)
            current_value = (current_value + days_of_the_month) % 7
            if m == 0:
                yield current_value
            elif y == 27:
                return

FIRST_WEEKDAY_OF_THE_YEAR = list(_calculate_first_days()) # 28 years cicle starting from 1972

class MyDateTime:
    def __init__(self, t: int = None, tz = None): 
        if t is None: 
            self._timestamp = t = int(time.time())
        else:
            self._timestamp = t = int(t)
        if tz is None: tz = datetime.datetime.now().astimezone().tzinfo
        t += int(tz.utcoffset(datetime.datetime.now()).total_seconds())
        self.tzinfo = tz

        leap_years_since_epoch, other_secs = divmod(t, SECONDS_EVERY_FOUR_YEARS)
        if other_secs > SECONDS_AFTER_FIRST_LEAP_YEAR:
            other_secs -= SECONDS_EVERY_DAY
        
        years, seconds_this_year = divmod(other_secs, SECONDS_EVERY_YEAR)
        days_this_year, seconds_this_day = divmod(seconds_this_year, SECONDS_EVERY_DAY)
        hours_this_day, seconds_this_hour = divmod(seconds_this_day, 3600)
        minutes_this_day, seconds_this_minute = divmod(seconds_this_hour, 60)
        ad_year = 1970 + leap_years_since_epoch * 4 + years
        weekday_index = (ad_year - 1972) % 28
        weeks_this_year, weekday = divmod(FIRST_WEEKDAY_OF_THE_YEAR[weekday_index] + days_this_year, 7)

        years_since_last_leap_year = years - 2
        for m in range(0, 12):
            days_of_the_month = _get_numbers_of_days_the_month(m, years_since_last_leap_year)
            if days_this_year <= days_of_the_month:
                days_this_month = days_this_year + 1
                months_this_year = m + 1
                break
            else:
                days_this_year -= days_of_the_month

        self.year = ad_year
        self.month = months_this_year
        self.day = days_this_month
        self.yday = days_this_year + 1
        self.wday = weekday
        self.isoweek = weeks_this_year
        self.hour = hours_this_day
        self.minute = minutes_this_day
        self.second = seconds_this_minute

    def timetuple(self):
        dst_d = self.tzinfo.dst(datetime.datetime.now())
        if dst_d is None: dst = -1
        else: dst = dst_d.total_seconds() / 3600
        return time.struct_time((self.year, self.month, self.day, self.hour, self.minute, self.second,
                                self.isoweek, self.yday, dst))

    def asctime(self): return time.asctime(self.timetuple())

    def __str__(self): return self.asctime()

    def __repr__(self):
        return f'<MyDateTime({self.year}, {self.month}, {self.day}, ' \
               f'{self.hour}, {self.minute}, {self.second}, ' \
               f'week={self.isoweek}, weekday={self.wday})>'