# Class Date supplies date objects that support date arithmetic.

#

# Date(month,day,year) returns a Date object.  An instance prints as,

# e.g., 'Mon 16 Aug 1993'.

#

# Addition, subtraction, comparison operators, min, max, and sorting

# all work as expected for date objects:  int+date or date+int returns

# the date `int' days from `date'; date+date raises an exception;

# date-int returns the date `int' days before `date'; date2-date1 returns

# an integer, the number of days from date1 to date2; int-date raises an

# exception; date1 < date2 is true iff date1 occurs before date2 (&

# similarly for other comparisons); min(date1,date2) is the earlier of

# the two dates and max(date1,date2) the later; and date objects can be

# used as dictionary keys.

#

# Date objects support one visible method, date.weekday().  This returns

# the day of the week the date falls on, as a string.

#

# Date objects also have 4 read-only data attributes:

#   .month  in 1..12

#   .day    in 1..31

#   .year   int or long int

#   .ord    the ordinal of the date relative to an arbitrary staring point

#

# The Dates module also supplies function today(), which returns the

# current date as a date object.

#

# Those entranced by calendar trivia will be disappointed, as no attempt

# has been made to accommodate the Julian (etc) system.  On the other

# hand, at least this package knows that 2000 is a leap year but 2100

# isn't, and works fine for years with a hundred decimal digits <wink>.

# Tim Peters   tim@ksr.com

# not speaking for Kendall Square Research Corp

# Adapted to Python 1.1 (where some hacks to overcome coercion are unnecessary)

# by Guido van Rossum

# Note that as of Python 2.3, a datetime module is included in the stardard

# library.

# vi:set tabsize=8:

_MONTH_NAMES = [ 'January', 'February', 'March', 'April', 'May',

                 'June', 'July', 'August', 'September', 'October',

                 'November', 'December' ]

_DAY_NAMES = [ 'Friday', 'Saturday', 'Sunday', 'Monday',

               'Tuesday', 'Wednesday', 'Thursday' ]

_DAYS_IN_MONTH = [ 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 ]

_DAYS_BEFORE_MONTH = []

dbm = 0

for dim in _DAYS_IN_MONTH:

    _DAYS_BEFORE_MONTH.append(dbm)

    dbm = dbm + dim

del dbm, dim

_INT_TYPES = type(1), type(1L)

def _is_leap(year):           # 1 if leap year, else 0

    if year % 4 != 0: return 0

    if year % 400 == 0: return 1

    return year % 100 != 0

def _days_in_year(year):      # number of days in year

    return 365 + _is_leap(year)

def _days_before_year(year):  # number of days before year

    return year*365L + (year+3)//4 - (year+99)//100 + (year+399)//400

def _days_in_month(month, year):      # number of days in month of year

    if month == 2 and _is_leap(year): return 29

    return _DAYS_IN_MONTH[month-1]

def _days_before_month(month, year):  # number of days in year before month

    return _DAYS_BEFORE_MONTH[month-1] + (month > 2 and _is_leap(year))

def _date2num(date):          # compute ordinal of date.month,day,year

    return _days_before_year(date.year) + \

           _days_before_month(date.month, date.year) + \

           date.day

_DI400Y = _days_before_year(400)      # number of days in 400 years

def _num2date(n):             # return date with ordinal n

    if type(n) not in _INT_TYPES:

        raise TypeError, 'argument must be integer: %r' % type(n)

    ans = Date(1,1,1)   # arguments irrelevant; just getting a Date obj

    del ans.ord, ans.month, ans.day, ans.year # un-initialize it

    ans.ord = n

    n400 = (n-1)//_DI400Y                # # of 400-year blocks preceding

    year, n = 400 * n400, n - _DI400Y * n400

    more = n // 365

    dby = _days_before_year(more)

    if dby >= n:

        more = more - 1

        dby = dby - _days_in_year(more)

    year, n = year + more, int(n - dby)

    try: year = int(year)               # chop to int, if it fits

    except (ValueError, OverflowError): pass

    month = min(n//29 + 1, 12)

    dbm = _days_before_month(month, year)

    if dbm >= n:

        month = month - 1

        dbm = dbm - _days_in_month(month, year)

    ans.month, ans.day, ans.year = month, n-dbm, year

    return ans

def _num2day(n):      # return weekday name of day with ordinal n

    return _DAY_NAMES[ int(n % 7) ]

class Date:

    def __init__(self, month, day, year):

        if not 1 <= month <= 12:

            raise ValueError, 'month must be in 1..12: %r' % (month,)

        dim = _days_in_month(month, year)

        if not 1 <= day <= dim:

            raise ValueError, 'day must be in 1..%r: %r' % (dim, day)

        self.month, self.day, self.year = month, day, year

        self.ord = _date2num(self)

    # don't allow setting existing attributes

    def __setattr__(self, name, value):

        if self.__dict__.has_key(name):

            raise AttributeError, 'read-only attribute ' + name

        self.__dict__[name] = value

    def __cmp__(self, other):

        return cmp(self.ord, other.ord)

    # define a hash function so dates can be used as dictionary keys

    def __hash__(self):

        return hash(self.ord)

    # print as, e.g., Mon 16 Aug 1993

    def __repr__(self):

        return '%.3s %2d %.3s %r' % (

              self.weekday(),

              self.day,

              _MONTH_NAMES[self.month-1],

              self.year)

    # Python 1.1 coerces neither int+date nor date+int

    def __add__(self, n):

        if type(n) not in _INT_TYPES:

            raise TypeError, 'can\'t add %r to date' % type(n)

        return _num2date(self.ord + n)

    __radd__ = __add__ # handle int+date

    # Python 1.1 coerces neither date-int nor date-date

    def __sub__(self, other):

        if type(other) in _INT_TYPES:           # date-int

            return _num2date(self.ord - other)

        else:

            return self.ord - other.ord         # date-date

    # complain about int-date

    def __rsub__(self, other):

        raise TypeError, 'Can\'t subtract date from integer'

    def weekday(self):

        return _num2day(self.ord)

def today():

    import time

    local = time.localtime(time.time())

    return Date(local[1], local[2], local[0])

class DateTestError(Exception):

    pass

def test(firstyear, lastyear):

    a = Date(9,30,1913)

    b = Date(9,30,1914)

    if repr(a) != 'Tue 30 Sep 1913':

        raise DateTestError, '__repr__ failure'

    if (not a < b) or a == b or a > b or b != b:

        raise DateTestError, '__cmp__ failure'

    if a+365 != b or 365+a != b:

        raise DateTestError, '__add__ failure'

    if b-a != 365 or b-365 != a:

        raise DateTestError, '__sub__ failure'

    try:

        x = 1 - a

        raise DateTestError, 'int-date should have failed'

    except TypeError:

        pass

    try:

        x = a + b

        raise DateTestError, 'date+date should have failed'

    except TypeError:

        pass

    if a.weekday() != 'Tuesday':

        raise DateTestError, 'weekday() failure'

    if max(a,b) is not b or min(a,b) is not a:

        raise DateTestError, 'min/max failure'

    d = {a-1:b, b:a+1}

    if d[b-366] != b or d[a+(b-a)] != Date(10,1,1913):

        raise DateTestError, 'dictionary failure'

    # verify date<->number conversions for first and last days for

    # all years in firstyear .. lastyear

    lord = _days_before_year(firstyear)

    y = firstyear

    while y <= lastyear:

        ford = lord + 1

        lord = ford + _days_in_year(y) - 1

        fd, ld = Date(1,1,y), Date(12,31,y)

        if (fd.ord,ld.ord) != (ford,lord):

            raise DateTestError, ('date->num failed', y)

        fd, ld = _num2date(ford), _num2date(lord)

        if (1,1,y,12,31,y) != \

           (fd.month,fd.day,fd.year,ld.month,ld.day,ld.year):

            raise DateTestError, ('num->date failed', y)

        y = y + 1

if __name__ == '__main__':

    test(1850, 2150)