1 # Class Date supplies date objects that support date arithmetic.

     2 #

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

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

     5 #

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

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

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

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

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

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

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

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

    14 # used as dictionary keys.

    15 #

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

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

    18 #

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

    20 #   .month  in 1..12

    21 #   .day    in 1..31

    22 #   .year   int or long int

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

    24 #

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

    26 # current date as a date object.

    27 #

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

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

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

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

    32 

    33 # Tim Peters   tim@ksr.com

    34 # not speaking for Kendall Square Research Corp

    35 

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

    37 # by Guido van Rossum

    38 

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

    40 # library.

    41 

    42 # vi:set tabsize=8:

    43 

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

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

    46                  'November', 'December' ]

    47 

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

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

    50 

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

    52 

    53 _DAYS_BEFORE_MONTH = []

    54 dbm = 0

    55 for dim in _DAYS_IN_MONTH:

    56     _DAYS_BEFORE_MONTH.append(dbm)

    57     dbm = dbm + dim

    58 del dbm, dim

    59 

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

    61 

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

    63     if year % 4 != 0: return 0

    64     if year % 400 == 0: return 1

    65     return year % 100 != 0

    66 

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

    68     return 365 + _is_leap(year)

    69 

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

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

    72 

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

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

    75     return _DAYS_IN_MONTH[month-1]

    76 

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

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

    79 

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

    81     return _days_before_year(date.year) + \

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

    83            date.day

    84 

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

    86 

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

    88     if type(n) not in _INT_TYPES:

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

    90 

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

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

    93     ans.ord = n

    94 

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

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

    97     more = n // 365

    98     dby = _days_before_year(more)

    99     if dby >= n:

   100         more = more - 1

   101         dby = dby - _days_in_year(more)

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

   103 

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

   105     except (ValueError, OverflowError): pass

   106 

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

   108     dbm = _days_before_month(month, year)

   109     if dbm >= n:

   110         month = month - 1

   111         dbm = dbm - _days_in_month(month, year)

   112 

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

   114     return ans

   115 

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

   117     return _DAY_NAMES[ int(n % 7) ]

   118 

   119 

   120 class Date:

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

   122         if not 1 <= month <= 12:

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

   124         dim = _days_in_month(month, year)

   125         if not 1 <= day <= dim:

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

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

   128         self.ord = _date2num(self)

   129 

   130     # don't allow setting existing attributes

   131     def __setattr__(self, name, value):

   132         if self.__dict__.has_key(name):

   133             raise AttributeError, 'read-only attribute ' + name

   134         self.__dict__[name] = value

   135 

   136     def __cmp__(self, other):

   137         return cmp(self.ord, other.ord)

   138 

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

   140     def __hash__(self):

   141         return hash(self.ord)

   142 

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

   144     def __repr__(self):

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

   146               self.weekday(),

   147               self.day,

   148               _MONTH_NAMES[self.month-1],

   149               self.year)

   150 

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

   152     def __add__(self, n):

   153         if type(n) not in _INT_TYPES:

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

   155         return _num2date(self.ord + n)

   156     __radd__ = __add__ # handle int+date

   157 

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

   159     def __sub__(self, other):

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

   161             return _num2date(self.ord - other)

   162         else:

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

   164 

   165     # complain about int-date

   166     def __rsub__(self, other):

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

   168 

   169     def weekday(self):

   170         return _num2day(self.ord)

   171 

   172 def today():

   173     import time

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

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

   176 

   177 class DateTestError(Exception):

   178     pass

   179 

   180 def test(firstyear, lastyear):

   181     a = Date(9,30,1913)

   182     b = Date(9,30,1914)

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

   184         raise DateTestError, '__repr__ failure'

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

   186         raise DateTestError, '__cmp__ failure'

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

   188         raise DateTestError, '__add__ failure'

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

   190         raise DateTestError, '__sub__ failure'

   191     try:

   192         x = 1 - a

   193         raise DateTestError, 'int-date should have failed'

   194     except TypeError:

   195         pass

   196     try:

   197         x = a + b

   198         raise DateTestError, 'date+date should have failed'

   199     except TypeError:

   200         pass

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

   202         raise DateTestError, 'weekday() failure'

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

   204         raise DateTestError, 'min/max failure'

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

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

   207         raise DateTestError, 'dictionary failure'

   208 

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

   210     # all years in firstyear .. lastyear

   211 

   212     lord = _days_before_year(firstyear)

   213     y = firstyear

   214     while y <= lastyear:

   215         ford = lord + 1

   216         lord = ford + _days_in_year(y) - 1

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

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

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

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

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

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

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

   224         y = y + 1

   225 

   226 if __name__ == '__main__':

   227     test(1850, 2150)