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 is 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]