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Editing: Dates.py
# 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)
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