/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 = []
 54dbm = 0
 55for dim in _DAYS_IN_MONTH:
 56    _DAYS_BEFORE_MONTH.append(dbm)
 57    dbm = dbm + dim
 58del dbm, dim
 59
 60_INT_TYPES = type(1), type(1L)
 61
 62def _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
 67def _days_in_year(year):      # number of days in year
 68    return 365 + _is_leap(year)
 69
 70def _days_before_year(year):  # number of days before year
 71    return year*365L + (year+3)//4 - (year+99)//100 + (year+399)//400
 72
 73def _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
 77def _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
 80def _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
 87def _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
116def _num2day(n):      # return weekday name of day with ordinal n
117    return _DAY_NAMES[ int(n % 7) ]
118
119
120class 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
172def today():
173    import time
174    local = time.localtime(time.time())
175    return Date(local[1], local[2], local[0])
176
177class DateTestError(Exception):
178    pass
179
180def 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
226if __name__ == '__main__':
227    test(1850, 2150)