# 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(1)
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*365 + (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 name in self.__dict__:
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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