Demo/classes/Dates.py

   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)