Lib/tzparse.py

"""Parse a timezone specification."""

# XXX Unfinished.
# XXX Only the typical form "XXXhhYYY;ddd/hh,ddd/hh" is currently supported.

tzpat = ('^([A-Z][A-Z][A-Z])([-+]?[0-9]+)([A-Z][A-Z][A-Z]);'
	  '([0-9]+)/([0-9]+),([0-9]+)/([0-9]+)$')

tzprog = None

def tzparse(tzstr):
	"""Given a timezone spec, return a tuple of information
	(tzname, delta, dstname, daystart, hourstart, dayend, hourend),
	where 'tzname' is the name of the timezone, 'delta' is the offset
	in hours from GMT, 'dstname' is the name of the daylight-saving
	timezone, and 'daystart'/'hourstart' and 'dayend'/'hourend'
	specify the starting and ending points for daylight saving time."""
	global tzprog
	if tzprog == None:
		import re
		tzprog = re.compile(tzpat)
	match = tzprog.match(tzstr)
	if not match:
		raise ValueError, 'not the TZ syntax I understand'
	subs = []
	for i in range(1, 8):
		subs.append(match.group(i))
	for i in (1, 3, 4, 5, 6):
		subs[i] = eval(subs[i])
	[tzname, delta, dstname, daystart, hourstart, dayend, hourend] = subs
	return (tzname, delta, dstname, daystart, hourstart, dayend, hourend)

def tzlocaltime(secs, params):
	"""Given a Unix time in seconds and a tuple of information about
	a timezone as returned by tzparse(), return the local time in the
	form (year, month, day, hour, min, sec, yday, wday, tzname)."""
	import time
	(tzname, delta, dstname, daystart, hourstart, dayend, hourend) = params
	year, month, days, hours, mins, secs, yday, wday, isdst = \
		time.gmtime(secs - delta*3600)
	if (daystart, hourstart) <= (yday+1, hours) < (dayend, hourend):
		tzname = dstname
		hours = hours + 1
	return year, month, days, hours, mins, secs, yday, wday, tzname

def tzset():
	"""Determine the current timezone from the "TZ" environment variable."""
	global tzparams, timezone, altzone, daylight, tzname
	import os
	tzstr = os.environ['TZ']
	tzparams = tzparse(tzstr)
	timezone = tzparams[1] * 3600
	altzone = timezone - 3600
	daylight = 1
	tzname = tzparams[0], tzparams[2]

def isdst(secs):
	"""Return true if daylight-saving time is in effect for the given
	Unix time in the current timezone."""
	import time
	(tzname, delta, dstname, daystart, hourstart, dayend, hourend) = \
		tzparams
	year, month, days, hours, mins, secs, yday, wday, isdst = \
		time.gmtime(secs - delta*3600)
	return (daystart, hourstart) <= (yday+1, hours) < (dayend, hourend)

tzset()

def localtime(secs):
	"""Get the local time in the current timezone."""
	return tzlocaltime(secs, tzparams)

def test():
	from time import asctime, gmtime
	import time, sys
	now = time.time()
	x = localtime(now)
	tm = x[:-1] + (0,)
	print 'now =', now, '=', asctime(tm), x[-1]
	now = now - now % (24*3600)
	if sys.argv[1:]: now = now + eval(sys.argv[1])
	x = gmtime(now)
	tm = x[:-1] + (0,)
	print 'gmtime =', now, '=', asctime(tm), 'yday =', x[-2]
	jan1 = now - x[-2]*24*3600
	x = localtime(jan1)
	tm = x[:-1] + (0,)
	print 'jan1 =', jan1, '=', asctime(tm), x[-1]
	for d in range(85, 95) + range(265, 275):
		t = jan1 + d*24*3600
		x = localtime(t)
		tm = x[:-1] + (0,)
		print 'd =', d, 't =', t, '=', asctime(tm), x[-1]