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descriptive comment into a docstring. Cast attributes to int in __init__. Use __new__ instead of deleting attributes to "uninitialize".
227 lines
7.5 KiB
Python
227 lines
7.5 KiB
Python
"""
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Class Date supplies date objects that support date arithmetic.
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Date(month,day,year) returns a Date object. An instance prints as,
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e.g., 'Mon 16 Aug 1993'.
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Addition, subtraction, comparison operators, min, max, and sorting
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all work as expected for date objects: int+date or date+int returns
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the date `int' days from `date'; date+date raises an exception;
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date-int returns the date `int' days before `date'; date2-date1 returns
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an integer, the number of days from date1 to date2; int-date raises an
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exception; date1 < date2 is true iff date1 occurs before date2 (&
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similarly for other comparisons); min(date1,date2) is the earlier of
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the two dates and max(date1,date2) the later; and date objects can be
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used as dictionary keys.
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Date objects support one visible method, date.weekday(). This returns
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the day of the week the date falls on, as a string.
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Date objects also have 4 read-only data attributes:
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.month in 1..12
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.day in 1..31
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.year int or long int
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.ord the ordinal of the date relative to an arbitrary staring point
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The Dates module also supplies function today(), which returns the
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current date as a date object.
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Those entranced by calendar trivia will be disappointed, as no attempt
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has been made to accommodate the Julian (etc) system. On the other
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hand, at least this package knows that 2000 is a leap year but 2100
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isn't, and works fine for years with a hundred decimal digits <wink>.
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Tim Peters tim@ksr.com
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not speaking for Kendall Square Research Corp
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Adapted to Python 1.1 (where some hacks to overcome coercion are unnecessary)
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by Guido van Rossum
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Note that as of Python 2.3, a datetime module is included in the stardard
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library.
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"""
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import functools
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_MONTH_NAMES = [ 'January', 'February', 'March', 'April', 'May',
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'June', 'July', 'August', 'September', 'October',
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'November', 'December' ]
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_DAY_NAMES = [ 'Friday', 'Saturday', 'Sunday', 'Monday',
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'Tuesday', 'Wednesday', 'Thursday' ]
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_DAYS_IN_MONTH = [ 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 ]
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_DAYS_BEFORE_MONTH = []
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dbm = 0
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for dim in _DAYS_IN_MONTH:
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_DAYS_BEFORE_MONTH.append(dbm)
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dbm = dbm + dim
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del dbm, dim
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def _is_leap(year): # 1 if leap year, else 0
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if year % 4 != 0: return 0
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if year % 400 == 0: return 1
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return year % 100 != 0
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def _days_in_year(year): # number of days in year
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return 365 + _is_leap(year)
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def _days_before_year(year): # number of days before year
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return year*365 + (year+3)//4 - (year+99)//100 + (year+399)//400
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def _days_in_month(month, year): # number of days in month of year
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if month == 2 and _is_leap(year): return 29
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return _DAYS_IN_MONTH[month-1]
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def _days_before_month(month, year): # number of days in year before month
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return _DAYS_BEFORE_MONTH[month-1] + (month > 2 and _is_leap(year))
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def _date2num(date): # compute ordinal of date.month,day,year
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return _days_before_year(date.year) + \
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_days_before_month(date.month, date.year) + \
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date.day
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_DI400Y = _days_before_year(400) # number of days in 400 years
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def _num2date(n): # return date with ordinal n
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if not isinstance(n, int):
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raise TypeError('argument must be integer: %r' % type(n))
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# Get uninitialized Date object. This is necesary because once
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# attributes are set, they cannot be changed.
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ans = Date.__new__(Date)
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ans.ord = n
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n400 = (n-1)//_DI400Y # # of 400-year blocks preceding
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year, n = 400 * n400, n - _DI400Y * n400
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more = n // 365
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dby = _days_before_year(more)
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if dby >= n:
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more = more - 1
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dby = dby - _days_in_year(more)
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year, n = year + more, n - dby
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month = min(n//29 + 1, 12)
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dbm = _days_before_month(month, year)
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if dbm >= n:
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month = month - 1
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dbm = dbm - _days_in_month(month, year)
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ans.month, ans.day, ans.year = month, n-dbm, year
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return ans
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def _num2day(n): # return weekday name of day with ordinal n
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return _DAY_NAMES[n % 7]
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@functools.total_ordering
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class Date:
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def __init__(self, month, day, year):
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if not 1 <= month <= 12:
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raise ValueError('month must be in 1..12: %r' % (month,))
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dim = _days_in_month(month, year)
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if not 1 <= day <= dim:
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raise ValueError('day must be in 1..%r: %r' % (dim, day))
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self.month, self.day, self.year = map(int, (month, day, year))
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self.ord = _date2num(self)
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# don't allow setting existing attributes
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def __setattr__(self, name, value):
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if name in self.__dict__:
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raise AttributeError('read-only attribute ' + name)
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self.__dict__[name] = value
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def __eq__(self, other):
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return self.ord == other.ord
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def __lt__(self, other):
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return self.ord < other.ord
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# define a hash function so dates can be used as dictionary keys
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def __hash__(self):
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return hash(self.ord)
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# print as, e.g., Mon 16 Aug 1993
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def __repr__(self):
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return '%.3s %2d %.3s %r' % (
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self.weekday(),
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self.day,
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_MONTH_NAMES[self.month-1],
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self.year)
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# Python 1.1 coerces neither int+date nor date+int
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def __add__(self, n):
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if not isinstance(n, int):
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raise TypeError('can\'t add %r to date' % type(n))
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return _num2date(self.ord + n)
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__radd__ = __add__ # handle int+date
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# Python 1.1 coerces neither date-int nor date-date
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def __sub__(self, other):
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if isinstance(other, int): # date-int
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return _num2date(self.ord - other)
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else:
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return self.ord - other.ord # date-date
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# complain about int-date
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def __rsub__(self, other):
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raise TypeError('Can\'t subtract date from integer')
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def weekday(self):
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return _num2day(self.ord)
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def today():
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import time
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local = time.localtime(time.time())
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return Date(local[1], local[2], local[0])
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class DateTestError(Exception):
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pass
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def test(firstyear, lastyear):
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a = Date(9,30,1913)
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b = Date(9,30,1914)
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if repr(a) != 'Tue 30 Sep 1913':
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raise DateTestError('__repr__ failure')
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if (not a < b) or a == b or a > b or b != b:
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raise DateTestError('__cmp__ failure')
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if a+365 != b or 365+a != b:
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raise DateTestError('__add__ failure')
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if b-a != 365 or b-365 != a:
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raise DateTestError('__sub__ failure')
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try:
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x = 1 - a
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raise DateTestError('int-date should have failed')
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except TypeError:
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pass
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try:
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x = a + b
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raise DateTestError('date+date should have failed')
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except TypeError:
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pass
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if a.weekday() != 'Tuesday':
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raise DateTestError('weekday() failure')
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if max(a,b) is not b or min(a,b) is not a:
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raise DateTestError('min/max failure')
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d = {a-1:b, b:a+1}
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if d[b-366] != b or d[a+(b-a)] != Date(10,1,1913):
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raise DateTestError('dictionary failure')
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# verify date<->number conversions for first and last days for
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# all years in firstyear .. lastyear
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lord = _days_before_year(firstyear)
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y = firstyear
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while y <= lastyear:
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ford = lord + 1
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lord = ford + _days_in_year(y) - 1
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fd, ld = Date(1,1,y), Date(12,31,y)
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if (fd.ord,ld.ord) != (ford,lord):
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raise DateTestError('date->num failed', y)
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fd, ld = _num2date(ford), _num2date(lord)
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if (1,1,y,12,31,y) != \
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(fd.month,fd.day,fd.year,ld.month,ld.day,ld.year):
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raise DateTestError('num->date failed', y)
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y = y + 1
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if __name__ == '__main__':
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test(1850, 2150)
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