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Edit File: tzfile.py
''' $Id: tzfile.py,v 1.8 2004/06/03 00:15:24 zenzen Exp $ ''' from datetime import datetime from struct import unpack, calcsize from pytz.tzinfo import StaticTzInfo, DstTzInfo, memorized_ttinfo from pytz.tzinfo import memorized_datetime, memorized_timedelta def _byte_string(s): """Cast a string or byte string to an ASCII byte string.""" return s.encode('ASCII') _NULL = _byte_string('\0') def _std_string(s): """Cast a string or byte string to an ASCII string.""" return str(s.decode('ASCII')) def build_tzinfo(zone, fp): head_fmt = '>4s c 15x 6l' head_size = calcsize(head_fmt) (magic, format, ttisgmtcnt, ttisstdcnt, leapcnt, timecnt, typecnt, charcnt) = unpack(head_fmt, fp.read(head_size)) # Make sure it is a tzfile(5) file assert magic == _byte_string('TZif'), 'Got magic %s' % repr(magic) # Read out the transition times, localtime indices and ttinfo structures. data_fmt = '>%(timecnt)dl %(timecnt)dB %(ttinfo)s %(charcnt)ds' % dict( timecnt=timecnt, ttinfo='lBB' * typecnt, charcnt=charcnt) data_size = calcsize(data_fmt) data = unpack(data_fmt, fp.read(data_size)) # make sure we unpacked the right number of values assert len(data) == 2 * timecnt + 3 * typecnt + 1 transitions = [memorized_datetime(trans) for trans in data[:timecnt]] lindexes = list(data[timecnt:2 * timecnt]) ttinfo_raw = data[2 * timecnt:-1] tznames_raw = data[-1] del data # Process ttinfo into separate structs ttinfo = [] tznames = {} i = 0 while i < len(ttinfo_raw): # have we looked up this timezone name yet? tzname_offset = ttinfo_raw[i + 2] if tzname_offset not in tznames: nul = tznames_raw.find(_NULL, tzname_offset) if nul < 0: nul = len(tznames_raw) tznames[tzname_offset] = _std_string( tznames_raw[tzname_offset:nul]) ttinfo.append((ttinfo_raw[i], bool(ttinfo_raw[i + 1]), tznames[tzname_offset])) i += 3 # Now build the timezone object if len(ttinfo) == 1 or len(transitions) == 0: ttinfo[0][0], ttinfo[0][2] cls = type(zone, (StaticTzInfo,), dict( zone=zone, _utcoffset=memorized_timedelta(ttinfo[0][0]), _tzname=ttinfo[0][2])) else: # Early dates use the first standard time ttinfo i = 0 while ttinfo[i][1]: i += 1 if ttinfo[i] == ttinfo[lindexes[0]]: transitions[0] = datetime.min else: transitions.insert(0, datetime.min) lindexes.insert(0, i) # calculate transition info transition_info = [] for i in range(len(transitions)): inf = ttinfo[lindexes[i]] utcoffset = inf[0] if not inf[1]: dst = 0 else: for j in range(i - 1, -1, -1): prev_inf = ttinfo[lindexes[j]] if not prev_inf[1]: break dst = inf[0] - prev_inf[0] # dst offset # Bad dst? Look further. DST > 24 hours happens when # a timzone has moved across the international dateline. if dst <= 0 or dst > 3600 * 3: for j in range(i + 1, len(transitions)): stdinf = ttinfo[lindexes[j]] if not stdinf[1]: dst = inf[0] - stdinf[0] if dst > 0: break # Found a useful std time. tzname = inf[2] # Round utcoffset and dst to the nearest minute or the # datetime library will complain. Conversions to these timezones # might be up to plus or minus 30 seconds out, but it is # the best we can do. utcoffset = int((utcoffset + 30) // 60) * 60 dst = int((dst + 30) // 60) * 60 transition_info.append(memorized_ttinfo(utcoffset, dst, tzname)) cls = type(zone, (DstTzInfo,), dict( zone=zone, _utc_transition_times=transitions, _transition_info=transition_info)) return cls() if __name__ == '__main__': import os.path from pprint import pprint # Patched in Debian, use the system zoninfo from the tzdata package base = '/usr/share/zoneinfo' tz = build_tzinfo('Australia/Melbourne', open(os.path.join(base, 'Australia', 'Melbourne'), 'rb')) tz = build_tzinfo('US/Eastern', open(os.path.join(base, 'US', 'Eastern'), 'rb')) pprint(tz._utc_transition_times)