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 # vi:set tabsize=8:
  40
  41 _MONTH_NAMES = [ 'January', 'February', 'March', 'April', 'May',
  42                  'June', 'July', 'August', 'September', 'October',
  43                  'November', 'December' ]
  44
  45 _DAY_NAMES = [ 'Friday', 'Saturday', 'Sunday', 'Monday',
  46                'Tuesday', 'Wednesday', 'Thursday' ]
  47
  48 _DAYS_IN_MONTH = [ 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 ]
  49
  50 _DAYS_BEFORE_MONTH = []
  51 dbm = 0
  52 for dim in _DAYS_IN_MONTH:
  53     _DAYS_BEFORE_MONTH.append(dbm)
  54     dbm = dbm + dim
  55 del dbm, dim
  56
  57 _INT_TYPES = type(1), type(1L)
  58
  59 def _is_leap( year ):           # 1 if leap year, else 0
  60     if year % 4 != 0: return 0
  61     if year % 400 == 0: return 1
  62     return year % 100 != 0
  63
  64 def _days_in_year( year ):      # number of days in year
  65     return 365 + _is_leap(year)
  66
  67 def _days_before_year( year ):  # number of days before year
  68     return year*365L + (year+3)/4 - (year+99)/100 + (year+399)/400
  69
  70 def _days_in_month( month, year ):      # number of days in month of year
  71     if month == 2 and _is_leap(year): return 29
  72     return _DAYS_IN_MONTH[month-1]
  73
  74 def _days_before_month( month, year ):  # number of days in year before month
  75     return _DAYS_BEFORE_MONTH[month-1] + (month > 2 and _is_leap(year))
  76
  77 def _date2num( date ):          # compute ordinal of date.month,day,year
  78     return _days_before_year( date.year ) + \
  79            _days_before_month( date.month, date.year ) + \
  80            date.day
  81
  82 _DI400Y = _days_before_year( 400 )      # number of days in 400 years
  83
  84 def _num2date( n ):             # return date with ordinal n
  85     if type(n) not in _INT_TYPES:
  86         raise TypeError, 'argument must be integer: ' + `type(n)`
  87
  88     ans = Date(1,1,1)   # arguments irrelevant; just getting a Date obj
  89     del ans.ord, ans.month, ans.day, ans.year # un-initialize it
  90     ans.ord = n
  91
  92     n400 = (n-1)/_DI400Y                # # of 400-year blocks preceding
  93     year, n = 400 * n400, n - _DI400Y * n400
  94     more = n / 365
  95     dby = _days_before_year( more )
  96     if dby >= n:
  97         more = more - 1
  98         dby = dby - _days_in_year( more )
  99     year, n = year + more, int(n - dby)
 100
 101     try: year = int(year)               # chop to int, if it fits
 102     except (ValueError, OverflowError): pass
 103
 104     month = min( n/29 + 1, 12 )
 105     dbm = _days_before_month( month, year )
 106     if dbm >= n:
 107         month = month - 1
 108         dbm = dbm - _days_in_month( month, year )
 109
 110     ans.month, ans.day, ans.year = month, n-dbm, year
 111     return ans
 112
 113 def _num2day( n ):      # return weekday name of day with ordinal n
 114     return _DAY_NAMES[ int(n % 7) ]
 115
 116
 117 class Date:
 118     def __init__( self, month, day, year ):
 119         if not 1 <= month <= 12:
 120             raise ValueError, 'month must be in 1..12: ' + `month`
 121         dim = _days_in_month( month, year )
 122         if not 1 <= day <= dim:
 123             raise ValueError, 'day must be in 1..' + `dim` + ': ' + `day`
 124         self.month, self.day, self.year = month, day, year
 125         self.ord = _date2num( self )
 126
 127     # don't allow setting existing attributes
 128     def __setattr__( self, name, value ):
 129         if self.__dict__.has_key(name):
 130             raise AttributeError, 'read-only attribute ' + name
 131         self.__dict__[name] = value
 132
 133     def __cmp__( self, other ):
 134         return cmp( self.ord, other.ord )
 135
 136     # define a hash function so dates can be used as dictionary keys
 137     def __hash__( self ):
 138         return hash( self.ord )
 139
 140     # print as, e.g., Mon 16 Aug 1993
 141     def __repr__( self ):
 142         return '%.3s %2d %.3s ' % (
 143               self.weekday(),
 144               self.day,
 145               _MONTH_NAMES[self.month-1] ) + `self.year`
 146
 147     # Python 1.1 coerces neither int+date nor date+int
 148     def __add__( self, n ):
 149         if type(n) not in _INT_TYPES:
 150             raise TypeError, 'can\'t add ' + `type(n)` + ' to date'
 151         return _num2date( self.ord + n )
 152     __radd__ = __add__ # handle int+date
 153
 154     # Python 1.1 coerces neither date-int nor date-date
 155     def __sub__( self, other ):
 156         if type(other) in _INT_TYPES:           # date-int
 157             return _num2date( self.ord - other )
 158         else:
 159             return self.ord - other.ord         # date-date
 160
 161     # complain about int-date
 162     def __rsub__( self, other ):
 163         raise TypeError, 'Can\'t subtract date from integer'
 164
 165     def weekday( self ):
 166         return _num2day( self.ord )
 167
 168 def today():
 169     import time
 170     local = time.localtime(time.time())
 171     return Date( local[1], local[2], local[0] )
 172
 173 DateTestError = 'DateTestError'
 174 def test( firstyear, lastyear ):
 175     a = Date(9,30,1913)
 176     b = Date(9,30,1914)
 177     if `a` != 'Tue 30 Sep 1913':
 178         raise DateTestError, '__repr__ failure'
 179     if (not a < b) or a == b or a > b or b != b:
 180         raise DateTestError, '__cmp__ failure'
 181     if a+365 != b or 365+a != b:
 182         raise DateTestError, '__add__ failure'
 183     if b-a != 365 or b-365 != a:
 184         raise DateTestError, '__sub__ failure'
 185     try:
 186         x = 1 - a
 187         raise DateTestError, 'int-date should have failed'
 188     except TypeError:
 189         pass
 190     try:
 191         x = a + b
 192         raise DateTestError, 'date+date should have failed'
 193     except TypeError:
 194         pass
 195     if a.weekday() != 'Tuesday':
 196         raise DateTestError, 'weekday() failure'
 197     if max(a,b) is not b or min(a,b) is not a:
 198         raise DateTestError, 'min/max failure'
 199     d = {a-1:b, b:a+1}
 200     if d[b-366] != b or d[a+(b-a)] != Date(10,1,1913):
 201         raise DateTestError, 'dictionary failure'
 202
 203     # verify date<->number conversions for first and last days for
 204     # all years in firstyear .. lastyear
 205
 206     lord = _days_before_year( firstyear )
 207     y = firstyear
 208     while y <= lastyear:
 209         ford = lord + 1
 210         lord = ford + _days_in_year(y) - 1
 211         fd, ld = Date(1,1,y), Date(12,31,y)
 212         if (fd.ord,ld.ord) != (ford,lord):
 213             raise DateTestError, ('date->num failed', y)
 214         fd, ld = _num2date(ford), _num2date(lord)
 215         if (1,1,y,12,31,y) != \
 216            (fd.month,fd.day,fd.year,ld.month,ld.day,ld.year):
 217             raise DateTestError, ('num->date failed', y)
 218         y = y + 1