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+# module calendar
+
+##############################
+# Calendar support functions #
+##############################
+
+# This is based on UNIX ctime() et al. (also Standard C and POSIX)
+# Subtle but crucial differences:
+# - the order of the elements of a 'struct tm' differs, to ease sorting
+# - months numbers are 1-12, not 0-11; month arrays have a dummy element 0
+# - Monday is the first day of the week (numbered 0)
+
+# These are really parameters of the 'time' module:
+epoch = 1970		# Time began on January 1 of this year (00:00:00 UCT)
+day_0 = 3		# The epoch begins on a Thursday (Monday = 0)
+
+# Return 1 for leap years, 0 for non-leap years
+def isleap(year):
+	return year % 4 = 0 and (year % 100 <> 0 or year % 400 = 0)
+
+# Constants for months referenced later
+January = 1
+February = 2
+
+# Number of days per month (except for February in leap years)
+mdays = (0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31)
+
+# Exception raised for bad input (with string parameter for details)
+error = 'calendar error'
+
+# Turn seconds since epoch into calendar time
+def gmtime(secs):
+	if secs < 0: raise error, 'negative input to gmtime()'
+	mins, secs = divmod(secs, 60)
+	hours, mins = divmod(mins, 60)
+	days, hours = divmod(hours, 24)
+	wday = (days + day_0) % 7
+	year = epoch
+	# XXX Most of the following loop can be replaced by one division
+	while 1:
+		yd = 365 + isleap(year)
+		if days < yd: break
+		days = days - yd
+		year = year + 1
+	yday = days
+	month = January
+	while 1:
+		md = mdays[month] + (month = February and isleap(year))
+		if days < md: break
+		days = days - md
+		month = month + 1
+	return year, month, days + 1, hours, mins, secs, yday, wday
+	# XXX Week number also?
+
+# Return number of leap years in range [y1, y2)
+# Assume y1 <= y2 and no funny (non-leap century) years
+def leapdays(y1, y2):
+	return (y2+3)/4 - (y1+3)/4
+
+# Inverse of gmtime():
+# Turn UCT calendar time (less yday, wday) into seconds since epoch
+def mktime(year, month, day, hours, mins, secs):
+	days = day - 1
+	for m in range(January, month): days = days + mdays[m]
+	if isleap(year) and month > February: days = days+1
+	days = days + (year-epoch)*365 + leapdays(epoch, year)
+	return ((days*24 + hours)*60 + mins)*60 + secs
+
+# Full and abbreviated names of weekdays
+day_name = ('Monday', 'Tuesday', 'Wednesday', 'Thursday')
+day_name = day_name + ('Friday', 'Saturday', 'Sunday')
+day_abbr = ('Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat', 'Sun')
+
+# Full and abbreviated of months (1-based arrays!!!)
+month_name =          ('', 'January',   'February', 'March',    'April')
+month_name = month_name + ('May',       'June',     'July',     'August')
+month_name = month_name + ('September', 'October',  'November', 'December')
+month_abbr =       ('   ', 'Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun')
+month_abbr = month_abbr + ('Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec')
+
+# Zero-fill string to two positions (helper for asctime())
+def dd(s):
+	while len(s) < 2: s = '0' + s
+	return s
+
+# Blank-fill string to two positions (helper for asctime())
+def zd(s):
+	while len(s) < 2: s = ' ' + s
+	return s
+
+# Turn calendar time as returned by gmtime() into a string
+# (the yday parameter is for compatibility with gmtime())
+def asctime(year, month, day, hours, mins, secs, yday, wday):
+	s = day_abbr[wday] + ' ' + month_abbr[month] + ' ' + zd(`day`)
+	s = s + ' ' + dd(`hours`) + ':' + dd(`mins`) + ':' + dd(`secs`)
+	return s + ' ' + `year`
+
+# Localization: Minutes West from Greenwich
+# timezone = -2*60	# Middle-European time with DST on
+timezone = 5*60		# EST (sigh -- THINK time() doesn't return UCT)
+
+# Local time ignores DST issues for now -- adjust 'timezone' to fake it
+def localtime(secs):
+	return gmtime(secs - timezone*60)
+
+# UNIX-style ctime (except it doesn't append '\n'!)
+def ctime(secs):
+	return asctime(localtime(secs))
+
+######################
+# Non-UNIX additions #
+######################
+
+# Calendar printing etc.
+
+# Return weekday (0-6 ~ Mon-Sun) for year (1970-...), month (1-12), day (1-31)
+def weekday(year, month, day):
+	secs = mktime(year, month, day, 0, 0, 0)
+	days = secs / (24*60*60)
+	return (days + day_0) % 7
+
+# Return weekday (0-6 ~ Mon-Sun) and number of days (28-31) for year, month
+def monthrange(year, month):
+	day1 = weekday(year, month, 1)
+	ndays = mdays[month] + (month = February and isleap(year))
+	return day1, ndays
+
+# Return a matrix representing a month's calendar
+# Each row represents a week; days outside this month are zero
+def _monthcalendar(year, month):
+	day1, ndays = monthrange(year, month)
+	rows = []
+	r7 = range(7)
+	day = 1 - day1
+	while day <= ndays:
+		row = [0, 0, 0, 0, 0, 0, 0]
+		for i in r7:
+			if 1 <= day <= ndays: row[i] = day
+			day = day + 1
+		rows.append(row)
+	return rows
+
+# Caching interface to _monthcalendar
+mc_cache = {}
+def monthcalendar(year, month):
+	key = `year` + month_abbr[month]
+	try:
+		return mc_cache[key]
+	except RuntimeError:
+		mc_cache[key] = ret = _monthcalendar(year, month)
+		return ret
+
+# Center a string in a field
+def center(str, width):
+	n = width - len(str)
+	if n < 0: return str
+	return ' '*(n/2) + str + ' '*(n-n/2)
+
+# XXX The following code knows that print separates items with space!
+
+# Print a single week (no newline)
+def prweek(week, width):
+	for day in week:
+		if day = 0: print ' '*width,
+		else:
+			if width > 2: print ' '*(width-3),
+			if day < 10: print '',
+			print day,
+
+# Return a header for a week
+def weekheader(width):
+	str = ''
+	for i in range(7):
+		if str: str = str + ' '
+		str = str + day_abbr[i%7][:width]
+	return str
+
+# Print a month's calendar
+def prmonth(year, month):
+	print weekheader(3)
+	for week in monthcalendar(year, month):
+		prweek(week, 3)
+		print
+
+# Spacing between month columns
+spacing = '    '
+
+# 3-column formatting for year calendars
+def format3c(a, b, c):
+	print center(a, 20), spacing, center(b, 20), spacing, center(c, 20)
+
+# Print a year's calendar
+def prcal(year):
+	header = weekheader(2)
+	format3c('', `year`, '')
+	for q in range(January, January+12, 3):
+		print
+		format3c(month_name[q], month_name[q+1], month_name[q+2])
+		format3c(header, header, header)
+		data = []
+		height = 0
+		for month in range(q, q+3):
+			cal = monthcalendar(year, month)
+			if len(cal) > height: height = len(cal)
+			data.append(cal)
+		for i in range(height):
+			for cal in data:
+				if i >= len(cal):
+					print ' '*20,
+				else:
+					prweek(cal[i], 2)
+				print spacing,
+			print