"""The dates module implements classes for representing and manipulating several date types. Contents -------- * :class:`Rounding` * :class:`BaseDate` * :class:`CalendarDateMixin` * :class:`JulianDay` * :class:`GregorianDate` * :class:`HebrewDate` Note ---- All instances of the classes in this module should be treated as read only. No attributes should be changed once they're created. """ import abc from datetime import date from numbers import Number from enum import Enum, auto from pyluach import utils from pyluach import gematria class Rounding(Enum): """Enumerator to provide options for rounding Hebrew dates. This provides constants to use as arguments for functions. It should not be instantiated. Attributes ---------- PREVIOUS_DAY If the day is the 30th and the month only has 29 days, round to the 29th of the month. NEXT_DAY If the day is the 30th and the month only has 29 days, round to the 1st of the next month. EXCEPTION If the day is the 30th and the month only has 29 days, raise a ValueError. """ PREVIOUS_DAY = auto() NEXT_DAY = auto() EXCEPTION = auto() class BaseDate(abc.ABC): """BaseDate is a base class for all date types. It provides the following arithmetic and comparison operators common to all child date types. =================== ================================================= Operation Result =================== ================================================= d2 = date1 + int New date ``int`` days after date1 d2 = date1 - int New date ``int`` days before date1 int = date1 - date2 Positive integer equal to the duration from date1 to date2 date1 > date2 True if date1 occurs later than date2 date1 < date2 True if date1 occurs earlier than date2 date1 == date2 True if date1 occurs on the same day as date2 date1 != date2 True if ``date1 == date2`` is False =================== ================================================= Any subclass of ``BaseDate`` can be compared to and diffed with any other subclass date. """ @property @abc.abstractmethod def jd(self): """Return julian day number. Returns ------- float The Julian day number at midnight (as ``n.5``). """ @abc.abstractmethod def to_heb(self): """Return Hebrew Date. Returns ------- HebrewDate """ def __hash__(self): return hash(repr(self)) def __add__(self, other): try: return JulianDay(self.jd + other)._to_x(self) except TypeError: return NotImplemented def __sub__(self, other): try: if isinstance(other, Number): return JulianDay(self.jd - other)._to_x(self) return int(abs(self.jd - other.jd)) except (AttributeError, TypeError): return NotImplemented def __eq__(self, other): try: return self.jd == other.jd except AttributeError: return NotImplemented def __ne__(self, other): try: return self.jd != other.jd except AttributeError: return NotImplemented def __lt__(self, other): try: return self.jd < other.jd except AttributeError: return NotImplemented def __gt__(self, other): try: return self.jd > other.jd except AttributeError: return NotImplemented def __le__(self, other): try: return self.jd <= other.jd except AttributeError: return NotImplemented def __ge__(self, other): try: return self.jd >= other.jd except AttributeError: return NotImplemented def weekday(self): """Return day of week as an integer. Returns ------- int An integer representing the day of the week with Sunday as 1 through Saturday as 7. """ return int(self.jd+.5+1) % 7 + 1 def isoweekday(self): """Return the day of the week corresponding to the iso standard. Returns ------- int An integer representing the day of the week where Monday is 1 and and Sunday is 7. """ weekday = self.weekday() if weekday == 1: return 7 return weekday - 1 def shabbos(self): """Return the Shabbos on or following the date. Returns ------- JulianDay, GregorianDate, or HebrewDate `self` if the date is Shabbos or else the following Shabbos as the same date type as called from. Examples -------- >>> heb_date = HebrewDate(5781, 3, 29) >>> greg_date = heb_date.to_greg() >>> heb_date.shabbos() HebrewDate(5781, 4, 2) >>> greg_date.shabbos() GregorianDate(2021, 6, 12) """ return self + (7 - self.weekday()) def _day_of_holiday(self, israel, hebrew=False): """Return the day of the holiday. Parameters ---------- israel : bool, optional hebrew : bool, optional Returns ------- str """ name = utils._festival_string(self, israel) if name is not None: holiday = utils._Days(name) if holiday is utils._Days.SHAVUOS and israel: return '' first_day = utils._first_day_of_holiday(holiday) if first_day: year = self.to_heb().year day = HebrewDate(year, *first_day) - self + 1 if hebrew: day = gematria._num_to_str(day) return str(day) return '' def fast_day(self, hebrew=False): """Return name of fast day of date. Parameters ---------- hebrew : bool, optional ``True`` if you want the fast day name in Hebrew letters. Default is ``False``, which returns the name transliterated into English. Returns ------- str or None The name of the fast day or ``None`` if the date is not a fast day. """ return utils._fast_day_string(self, hebrew) def festival( self, israel=False, hebrew=False, include_working_days=True, prefix_day=False ): """Return name of Jewish festival of date. This method will return all major and minor religous Jewish holidays not including fast days. Parameters ---------- israel : bool, optional ``True`` if you want the holidays according to the Israel schedule. Defaults to ``False``. hebrew : bool, optional ``True`` if you want the festival name in Hebrew letters. Default is ``False``, which returns the name transliterated into English. include_working_days : bool, optional ``True`` to include festival days on which melacha (work) is allowed; ie. Pesach Sheni, Chol Hamoed, etc. Default is ``True``. prefix_day : bool, optional ``True`` to prefix multi day festivals with the day of the festival. Default is ``False``. Examples -------- >>> pesach = HebrewDate(2023, 1, 15) >>> pesach.festival(prefix_day=True) '1 Pesach' >>> pesach.festival(hebrew=True, prefix_day=True) 'א׳ פסח' >>> shavuos = HebrewDate(5783, 3, 6) >>> shavuos.festival(israel=True, prefix_day=True) 'Shavuos' Returns ------- str or None The name of the festival or ``None`` if the given date is not a Jewish festival. """ name = utils._festival_string( self, israel, hebrew, include_working_days ) if prefix_day and name is not None: day = self._day_of_holiday(israel=israel, hebrew=hebrew) if day: return f'{day} {name}' return name def holiday(self, israel=False, hebrew=False, prefix_day=False): """Return name of Jewish holiday of the date. The holidays include the major and minor religious Jewish holidays including fast days. Parameters ---------- israel : bool, optional ``True`` if you want the holidays according to the Israel schedule. Defaults to ``False``. hebrew : bool, optional ``True`` if you want the holiday name in Hebrew letters. Default is ``False``, which returns the name transliterated into English. prefix_day : bool, optional ``True`` to prefix multi day holidays with the day of the holiday. Default is ``False``. Examples -------- >>> pesach = HebrewDate(2023, 1, 15) >>> pesach.holiday(prefix_day=True) '1 Pesach' >>> pesach.holiday(hebrew=True, prefix_day=True) 'א׳ פסח' >>> taanis_esther = HebrewDate(5783, 12, 13) >>> taanis_esther.holiday(prefix_day=True) 'Taanis Esther' Returns ------- str or None The name of the holiday or ``None`` if the given date is not a Jewish holiday. """ return ( self.fast_day(hebrew=hebrew) or self.festival(israel, hebrew, prefix_day=prefix_day) ) class CalendarDateMixin: """CalendarDateMixin is a mixin for Hebrew and Gregorian dates. Parameters ---------- year : int month : int day : int Attributes ---------- year : int month : int day : int jd : float The equivalent Julian day at midnight. """ def __init__(self, year, month, day, jd=None): self.year = year self.month = month self.day = day self._jd = jd def __repr__(self): class_name = self.__class__.__name__ return f'{class_name}({self.year}, {self.month}, {self.day})' def __str__(self): return f'{self.year:04d}-{self.month:02d}-{self.day:02d}' def __iter__(self): yield self.year yield self.month yield self.day def tuple(self): """Return date as tuple. Returns ------- tuple of ints A tuple of ints in the form ``(year, month, day)``. """ return (self.year, self.month, self.day) def dict(self): """Return the date as a dictionary. Returns ------- dict A dictionary in the form ``{'year': int, 'month': int, 'day': int}``. """ return {'year': self.year, 'month': self.month, 'day': self.day} def replace(self, year=None, month=None, day=None): """Return new date with new values for the specified field. Parameters ---------- year : int, optional month: int, optional day : int, optional Returns ------- CalendarDateMixin Any date that inherits from CalendarDateMixin (``GregorianDate``, ````HebrewDate``). Raises ValueError Raises a ``ValueError`` if the new date does not exist. """ if year is None: year = self.year if month is None: month = self.month if day is None: day = self.day return type(self)(year, month, day) class JulianDay(BaseDate): """A JulianDay object represents a Julian Day at midnight. Parameters ---------- day : float or int The julian day. Note that Julian days start at noon so day number 10 is represented as 9.5 which is day 10 at midnight. Attributes ---------- day : float The Julian Day Number at midnight (as *n*.5) """ def __init__(self, day): if day-int(day) < .5: self.day = int(day) - .5 else: self.day = int(day) + .5 def __repr__(self): return f'JulianDay({self.day})' def __str__(self): return str(self.day) @property def jd(self): """Return julian day. Returns ------- float """ return self.day @staticmethod def from_pydate(pydate): """Return a `JulianDay` from a python date object. Parameters ---------- pydate : datetime.date A python standard library ``datetime.date`` instance Returns ------- JulianDay """ return GregorianDate.from_pydate(pydate).to_jd() @staticmethod def today(): """Return instance of current Julian day from timestamp. Extends the built-in ``datetime.date.today()``. Returns ------- JulianDay A JulianDay instance representing the current Julian day from the timestamp. Warning ------- Julian Days change at noon, but pyluach treats them as if they change at midnight, so at midnight this method will return ``JulianDay(n.5)`` until the following midnight when it will return ``JulianDay(n.5 + 1)``. """ return GregorianDate.today().to_jd() def to_greg(self): """Convert JulianDay to a Gregorian Date. Returns ------- GregorianDate The equivalent Gregorian date instance. Notes ----- This method uses the Fliegel-Van Flandern algorithm. """ jd = int(self.day + .5) L = jd + 68569 n = 4*L // 146097 L = L - (146097*n + 3) // 4 i = (4000 * (L+1)) // 1461001 L = L - ((1461*i) // 4) + 31 j = (80*L) // 2447 day = L - 2447*j // 80 L = j // 11 month = j + 2 - 12*L year = 100 * (n-49) + i + L if year < 1: year -= 1 return GregorianDate(year, month, day, self.day) def to_heb(self): """ Convert to a Hebrew date. Returns ------- HebrewDate The equivalent Hebrew date instance. """ if self.day <= 347997: raise ValueError('Date is before creation') jd = int(self.day + .5) # Try to account for half day jd -= 347997 year = int(jd//365) + 2 # try that to debug early years first_day = utils._elapsed_days(year) while first_day > jd: year -= 1 first_day = utils._elapsed_days(year) months = utils._monthslist(year) days_remaining = jd - first_day for month in months: if days_remaining >= utils._month_length(year, month): days_remaining -= utils._month_length(year, month) else: return HebrewDate(year, month, days_remaining + 1, self.day) def _to_x(self, type_): """Return a date object of the given type.""" if isinstance(type_, GregorianDate): return self.to_greg() if isinstance(type_, HebrewDate): return self.to_heb() if isinstance(type_, JulianDay): return self raise TypeError( 'This method has not been implemented with that type.' ) def to_pydate(self): """Convert to a datetime.date object. Returns ------- datetime.date A standard library ``datetime.date`` instance. """ return self.to_greg().to_pydate() class GregorianDate(BaseDate, CalendarDateMixin): """A GregorianDate object represents a Gregorian date (year, month, day). This is an idealized date with the current Gregorian calendar infinitely extended in both directions. Parameters ---------- year : int month : int day : int jd : float, optional This parameter should not be assigned manually. Attributes ---------- year : int month : int day : int Warnings -------- Although B.C.E. dates are allowed, they should be treated as approximations as they may return inconsistent results when converting between date types and using arithmetic and comparison operators! """ def __init__(self, year, month, day, jd=None): """Initialize a GregorianDate. This initializer extends the CalendarDateMixin initializer adding in date validation specific to Gregorian dates. """ if month < 1 or month > 12: raise ValueError(f'{str(month)} is an invalid month.') monthlength = self._monthlength(year, month) if day < 1 or day > monthlength: raise ValueError(f'Given month has {monthlength} days.') super().__init__(year, month, day, jd) def __format__(self, fmt): return self.strftime(fmt) def strftime(self, fmt): """Return formatted date. Wraps :py:meth:`datetime.date.strftime` method and uses the same format options. Parameters ---------- fmt : str The format string. Returns ------- str """ return self.to_pydate().strftime(fmt) @property def jd(self): """Return the corresponding Julian day number. Returns ------- float The Julian day number at midnight. """ if self._jd is None: year = self.year month = self.month day = self.day if year < 0: year += 1 if month < 3: year -= 1 month += 12 month += 1 a = year // 100 b = 2 - a + a//4 self._jd = ( int(365.25*year) + int(30.6001*month) + b + day + 1720994.5 ) return self._jd @classmethod def from_pydate(cls, pydate): """Return a `GregorianDate` instance from a python date object. Parameters ---------- pydate : datetime.date A python standard library ``datetime.date`` instance. Returns ------- GregorianDate """ return cls(*pydate.timetuple()[:3]) @staticmethod def today(): """Return a GregorianDate instance for the current day. This static method wraps the Python standard library's date.today() method to get the date from the timestamp. Returns ------- GregorianDate The current Gregorian date from the computer's timestamp. """ return GregorianDate.from_pydate(date.today()) @staticmethod def _is_leap(year): """Return True if year of date is a leap year, otherwise False.""" if year < 0: year += 1 if (year % 4 == 0) and not (year % 100 == 0 and year % 400 != 0): return True return False def is_leap(self): """Return if the date is in a leap year Returns ------- bool True if the date is in a leap year, False otherwise. """ return self._is_leap(self.year) @classmethod def _monthlength(cls, year, month): if month in [1, 3, 5, 7, 8, 10, 12]: return 31 if month == 2: if cls._is_leap(year): return 29 return 28 return 30 def to_jd(self): """Convert to a Julian day. Returns ------- JulianDay The equivalent JulianDay instance. """ return JulianDay(self.jd) def to_heb(self): """Convert to Hebrew date. Returns ------- HebrewDate The equivalent HebrewDate instance. """ return self.to_jd().to_heb() def to_pydate(self): """Convert to a standard library date. Returns ------- datetime.date The equivalent datetime.date instance. """ return date(*self.tuple()) class HebrewDate(BaseDate, CalendarDateMixin): """A class for manipulating Hebrew dates. The following format options are available similar to strftime: ====== ======= =========================================================== Format Example Meaning ====== ======= =========================================================== %a Sun Weekday as locale's abbreviated name %A Sunday Weekday as locale's full name %w 1 Weekday as decimal number 1-7 Sunday-Shabbos %d 07 Day of the month as a 0-padded 2 digit decimal number %-d 7 Day of the month as a decimal number %B Iyar Month name transliterated into English %m 02 Month as a 0-padded 2 digit decimal number %-m 2 Month as a decimal number %y 82, 01 Year without century as a zero-padded decimal number %Y 5782 Year as a decimal number %*a א׳ Weekday as a Hebrew numeral %*A ראשון Weekday name in Hebrew %*d ז׳, ט״ז Day of month as Hebrew numeral %*-d א, טו Day of month without gershayim %*B אייר Name of month in Hebrew %*y תשפ״ב Year in Hebrew numerals without the thousands place %*Y ה'תשפ״ב Year in Hebrew numerals with the thousands place %% % A literal '%' character ====== ======= =========================================================== Example ------- >>> date = HebrewDate(5783, 1, 15) >>> f'Today is {date:%a - %*-d %*B, %*y}' 'Today is Thu - טו אייר, תשפ"ג' Parameters ---------- year : int The Hebrew year. month : int The Hebrew month starting with Nissan as 1 (and Tishrei as 7). If there is a second Adar in the year it is has a value of 13. day : int The Hebrew day of the month. jd : float, optional This parameter should not be assigned manually. Attributes ---------- year : int month : int The Hebrew month starting with Nissan as 1 (and Tishrei as 7). If there is a second Adar it has a value of 13. day : int The day of the month. Raises ------ ValueError If the year is less than 1, if the month is less than 1 or greater than the last month, or if the day does not exist in the month a ``ValueError`` will be raised. """ def __init__(self, year, month, day, jd=None): """Initialize a HebrewDate instance. This initializer extends the CalendarDateMixin adding validation specific to hebrew dates. """ if year < 1: raise ValueError('Year must be >= 1.') if month < 1 or month > 13: raise ValueError(f'{month} is an invalid month.') if (not utils._is_leap(year)) and month == 13: raise ValueError(f'{year} is not a leap year') monthlength = utils._month_length(year, month) if day < 1 or day > monthlength: raise ValueError(f'Given month has {monthlength} days.') super().__init__(year, month, day, jd) def __format__(self, fmt): new = [] i = 0 while i < len(fmt): if fmt[i] != '%': new.append(fmt[i]) else: i += 1 try: curr = fmt[i] except IndexError as e: raise ValueError( 'Format string cannot end with single "%".' ) from e if curr == '%': new.append('%') elif curr == '*': i += 1 try: curr = fmt[i] except IndexError as e: raise ValueError( 'Format string cannot end with "%*".' ) from e if curr == '-': i += 1 try: curr = fmt[i] except IndexError as e: raise ValueError( 'Format string cannot end with "%*-"' ) from e if curr == 'd': new.append(self.hebrew_day(False)) else: raise ValueError('Invalid format string.') elif curr == 'a': new.append(gematria._num_to_str(self.weekday())) elif curr == 'A': new.append(utils.WEEKDAYS[self.weekday()]) elif curr == 'd': new.append(self.hebrew_day()) elif curr == 'B': new.append(self.month_name(True)) elif curr.casefold() == 'y': new.append(self.hebrew_year(curr == 'Y')) else: raise ValueError('Invalid format string.') elif curr == '-': i += 1 try: curr = fmt[i] except IndexError as e: raise ValueError( 'Format string cannot end with "%-"' ) from e if curr == 'd': new.append(str(self.day)) elif curr == 'm': new.append(str(self.month)) else: raise ValueError('Invalid format string.') else: if curr.casefold() == 'a': new.append(self.to_pydate().strftime(f'%{curr}')) elif curr == 'w': new.append(str(self.weekday())) elif curr == 'd': new.append(format(self.day, '02d')) elif curr == 'B': new.append(self.month_name(False)) elif curr == 'm': new.append(format(self.month, '02d')) elif curr.casefold() == 'y': new.append(date(self.year, 1, 1).strftime(f'%{curr}')) else: raise ValueError('Invalid format string.') i += 1 return ''.join(new) @property def jd(self): """Return the corresponding Julian day number. Returns ------- float The Julian day number at midnight. """ if self._jd is None: months = utils._monthslist(self.year) jd = utils._elapsed_days(self.year) for m in months: if m != self.month: jd += utils._month_length(self.year, m) else: self._jd = jd + (self.day-1) + 347996.5 return self._jd @staticmethod def from_pydate(pydate): """Return a `HebrewDate` from a python date object. Parameters ---------- pydate : datetime.date A python standard library ``datetime.date`` instance Returns ------- HebrewDate """ return GregorianDate.from_pydate(pydate).to_heb() @staticmethod def today(): """Return HebrewDate instance for the current day. This static method wraps the Python standard library's ``date.today()`` method to get the date from the timestamp. Returns ------- HebrewDate The current Hebrew date from the computer's timestamp. Warning ------- Pyluach treats Hebrew dates as if they change at midnight. If it's after nightfall but before midnight, to get the true Hebrew date do ``HebrewDate.today() + 1``. """ return GregorianDate.today().to_heb() def to_jd(self): """Convert to a Julian day. Returns ------- JulianDay The equivalent JulianDay instance. """ return JulianDay(self.jd) def to_greg(self): """Convert to a Gregorian date. Returns ------- GregorianDate The equivalent GregorianDate instance. """ return self.to_jd().to_greg() def to_pydate(self): """Convert to a standard library date. Returns ------- datetime.date The equivalent datetime.date instance. """ return self.to_greg().to_pydate() def to_heb(self): return self def month_name(self, hebrew=False): """Return the name of the month. Parameters ---------- hebrew : bool, optional ``True`` if the month name should be in Hebrew characters. Default is ``False`` which returns the month name transliterated into English. Returns ------- str """ return utils._month_name(self.year, self.month, hebrew) def hebrew_day(self, withgershayim=True): """Return the day of the month in Hebrew letters. Parameters ---------- withgershayim : bool, optional Default is ``True`` which includes a geresh with a single character and gershayim between two characters. Returns ------- str The day of the month in Hebrew letters. Examples -------- >>> date = HebrewDate(5782, 3, 6) >>> date.hebrew_day() 'ו׳' >>> date.hebrew_day(False) 'ו' >>> HebrewDate(5783, 12, 14).hebrew_day() 'י״ד' """ return gematria._num_to_str(self.day, withgershayim=withgershayim) def hebrew_year(self, thousands=False, withgershayim=True): """Return the year in Hebrew letters. Parameters ---------- thousands : bool ``True`` to prefix the year with a letter for the thousands place, ie. 'ה׳תשפ״א'. Default is ``False``. withgershayim : bool, optional Default is ``True`` which includes a geresh after the thousands place if applicable and a gershayim before the last character of the year. Returns ------- str """ return gematria._num_to_str(self.year, thousands, withgershayim) def hebrew_date_string(self, thousands=False): """Return a Hebrew string representation of the date. The date is in the form ``f'{day} {month} {year}'``. Parameters ---------- thousands : bool ``True`` to have the thousands include in the year. Default is ``False``. Returns ------- str Examples -------- >>> date = HebrewDate(5781, 9, 25) >>> date.hebrew_date_string() 'כ״ה כסלו תשפ״א' >>> date.hebrew_date_string(True) 'כ״ה כסלו ה׳תשפ״א' """ day = self.hebrew_day() month = self.month_name(True) year = self.hebrew_year(thousands) return f'{day} {month} {year}' def add( self, years=0, months=0, days=0, adar1=False, rounding=Rounding.NEXT_DAY ): """Add years, months, and days to date. Parameters ---------- years : int, optional The number of years to add. Default is 0. months : int, optional The number of months to add. Default is 0. days : int, optional The number of days to add. Default is 0. adar1 : bool, optional True to return a date in Adar Aleph if `self` is in a regular Adar and after adding the years it's leap year. Default is ``False`` which will return the date in Adar Beis. rounding : Rounding, optional Choose what to do if self is the 30th day of the month, and there are only 29 days in the destination month. :obj:`Rounding.NEXT_DAY` to return the first day of the next month. :obj:`Rounding.PREVIOUS_DAY` to return the last day of the month. :obj:`Rounding.EXCEPTION` to raise a ValueError. Default is :obj:`Rounding.NEXT_DAY`. Returns ------- HebrewDate Note ---- This method first adds the `years`. If the starting month is Adar and the destination year has two Adars, it chooses which one based on the `adar1` argument, then it adds the `months`. If the starting day doesn't exist in that month it adjusts it based on the `rounding` argument, then it adds the `days`. Examples -------- >>> date = HebrewDate(5783, 11, 30) >>> date.add(months=1) HebrewDate(5783, 1, 1) >>> date.add(months=1, rounding=Rounding.PREVIOUS_DAY) HebrewDate(5783, 12, 29) """ year = self.year + years month = self.month if self.month == 13 and not utils._is_leap(year): month = 12 elif ( self.month == 12 and not utils._is_leap(self.year) and utils._is_leap(year) and not adar1 ): month = 13 if months > 0: year, month = utils._add_months(year, month, months) elif months < 0: year, month = utils._subtract_months(year, month, -months) if utils._month_length(year, month) < self.day: date = HebrewDate(year, month, 29) if rounding is Rounding.EXCEPTION: raise ValueError(f'{date:%B %Y} has only 29 days.') if rounding is Rounding.NEXT_DAY: date += 1 elif not isinstance(rounding, Rounding): raise TypeError( 'The rounding argument can only be a member of the' ' dates.Rounding enum.' ) else: date = HebrewDate(year, month, self.day) return date + days def subtract( self, years=0, months=0, days=0, adar1=False, rounding=Rounding.NEXT_DAY ): """Subtract years, months, and days from date. Parameters ---------- years : int, optional The number of years to subtract. Default is 0. months : int, optional The number of months to subtract. Default is 0. days : int, optional The number of days to subtract. Default is 0. adar1 : bool, optional True to return a date in Adar Aleph if `self` is in a regular Adar and the destination year is leap year. Default is ``False`` which will return the date in Adar Beis. rounding : Rounding, optional Choose what to do if self is the 30th day of the month, and there are only 29 days in the destination month. :obj:`Rounding.NEXT_DAY` to return the first day of the next month. :obj:`Rounding.PREVIOUS_DAY` to return the last day of the month. :obj:`Rounding.EXCEPTION` to raise a ValueError. Default is :obj:`Rounding.NEXT_DAY`. Returns ------- HebrewDate Note ---- This method first subtracts the `years`. If the starting month is Adar and the destination year has two Adars, it chooses which one based on the `adar1` argument, then it subtracts the `months`. If the starting day doesn't exist in that month it adjusts it based on the `rounding` argument, then it subtracts the `days`. """ return self.add(-years, -months, -days, adar1, rounding)