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1 '''
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2 $Id: tzfile.py,v 1.8 2004/06/03 00:15:24 zenzen Exp $
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3 '''
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4
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5 from datetime import datetime
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6 from struct import unpack, calcsize
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7
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8 from pytz.tzinfo import StaticTzInfo, DstTzInfo, memorized_ttinfo
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9 from pytz.tzinfo import memorized_datetime, memorized_timedelta
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10
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11
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12 def _byte_string(s):
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13 """Cast a string or byte string to an ASCII byte string."""
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14 return s.encode('ASCII')
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15
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16 _NULL = _byte_string('\0')
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17
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18
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19 def _std_string(s):
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20 """Cast a string or byte string to an ASCII string."""
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21 return str(s.decode('ASCII'))
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22
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23
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24 def build_tzinfo(zone, fp):
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25 head_fmt = '>4s c 15x 6l'
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26 head_size = calcsize(head_fmt)
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27 (magic, format, ttisgmtcnt, ttisstdcnt, leapcnt, timecnt,
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28 typecnt, charcnt) = unpack(head_fmt, fp.read(head_size))
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29
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30 # Make sure it is a tzfile(5) file
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31 assert magic == _byte_string('TZif'), 'Got magic %s' % repr(magic)
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32
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33 # Read out the transition times, localtime indices and ttinfo structures.
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34 data_fmt = '>%(timecnt)dl %(timecnt)dB %(ttinfo)s %(charcnt)ds' % dict(
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35 timecnt=timecnt, ttinfo='lBB' * typecnt, charcnt=charcnt)
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36 data_size = calcsize(data_fmt)
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37 data = unpack(data_fmt, fp.read(data_size))
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38
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39 # make sure we unpacked the right number of values
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40 assert len(data) == 2 * timecnt + 3 * typecnt + 1
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41 transitions = [memorized_datetime(trans)
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42 for trans in data[:timecnt]]
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43 lindexes = list(data[timecnt:2 * timecnt])
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44 ttinfo_raw = data[2 * timecnt:-1]
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45 tznames_raw = data[-1]
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46 del data
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47
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48 # Process ttinfo into separate structs
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49 ttinfo = []
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50 tznames = {}
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51 i = 0
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52 while i < len(ttinfo_raw):
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53 # have we looked up this timezone name yet?
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54 tzname_offset = ttinfo_raw[i + 2]
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55 if tzname_offset not in tznames:
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56 nul = tznames_raw.find(_NULL, tzname_offset)
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57 if nul < 0:
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58 nul = len(tznames_raw)
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59 tznames[tzname_offset] = _std_string(
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60 tznames_raw[tzname_offset:nul])
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61 ttinfo.append((ttinfo_raw[i],
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62 bool(ttinfo_raw[i + 1]),
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63 tznames[tzname_offset]))
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64 i += 3
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65
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66 # Now build the timezone object
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67 if len(ttinfo) == 1 or len(transitions) == 0:
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68 ttinfo[0][0], ttinfo[0][2]
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69 cls = type(zone, (StaticTzInfo,), dict(
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70 zone=zone,
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71 _utcoffset=memorized_timedelta(ttinfo[0][0]),
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72 _tzname=ttinfo[0][2]))
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73 else:
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74 # Early dates use the first standard time ttinfo
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75 i = 0
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76 while ttinfo[i][1]:
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77 i += 1
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78 if ttinfo[i] == ttinfo[lindexes[0]]:
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79 transitions[0] = datetime.min
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80 else:
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81 transitions.insert(0, datetime.min)
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82 lindexes.insert(0, i)
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83
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84 # calculate transition info
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85 transition_info = []
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86 for i in range(len(transitions)):
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87 inf = ttinfo[lindexes[i]]
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88 utcoffset = inf[0]
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89 if not inf[1]:
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90 dst = 0
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91 else:
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92 for j in range(i - 1, -1, -1):
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93 prev_inf = ttinfo[lindexes[j]]
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94 if not prev_inf[1]:
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95 break
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96 dst = inf[0] - prev_inf[0] # dst offset
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97
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98 # Bad dst? Look further. DST > 24 hours happens when
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99 # a timzone has moved across the international dateline.
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100 if dst <= 0 or dst > 3600 * 3:
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101 for j in range(i + 1, len(transitions)):
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102 stdinf = ttinfo[lindexes[j]]
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103 if not stdinf[1]:
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104 dst = inf[0] - stdinf[0]
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105 if dst > 0:
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106 break # Found a useful std time.
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107
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108 tzname = inf[2]
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109
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110 # Round utcoffset and dst to the nearest minute or the
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111 # datetime library will complain. Conversions to these timezones
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112 # might be up to plus or minus 30 seconds out, but it is
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113 # the best we can do.
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114 utcoffset = int((utcoffset + 30) // 60) * 60
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115 dst = int((dst + 30) // 60) * 60
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116 transition_info.append(memorized_ttinfo(utcoffset, dst, tzname))
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117
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118 cls = type(zone, (DstTzInfo,), dict(
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119 zone=zone,
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120 _utc_transition_times=transitions,
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121 _transition_info=transition_info))
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122
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123 return cls()
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124
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125 if __name__ == '__main__':
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126 import os.path
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127 from pprint import pprint
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128 base = os.path.join(os.path.dirname(__file__), 'zoneinfo')
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129 tz = build_tzinfo('Australia/Melbourne',
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130 open(os.path.join(base, 'Australia', 'Melbourne'), 'rb'))
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131 tz = build_tzinfo('US/Eastern',
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132 open(os.path.join(base, 'US', 'Eastern'), 'rb'))
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133 pprint(tz._utc_transition_times)
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