从tzdata提取历史leap秒

从tzdata提取历史leap秒

我只是做了一下

man 5 tzfile

，计算了一个偏移量，该偏移量将找到the秒信息，然后读取the秒信息。

您可以取消注释“ DEBUG：”打印语句，以查看它在文件中找到的更多内容。

编辑：程序更新为现在正确。现在

/usr/share/zoneinfo/right/UTC

，它使用该文件，并且现在找到要打印的leap秒。

原始程序并未跳过在手册页中记录的timezeone缩写字符，但有些隐藏（“
…，并且tt_abbrind充当时区缩写字符数组的索引，该数组遵循ttinfo结构中的文件。”）。

import datetimeimport structTZFILE_MAGIC = 'TZif'.enpre('US-ASCII')def leap_seconds(f):    """    Return a list of tuples of this format: (timestamp, number_of_seconds)        timestamp: a 32-bit timestamp, seconds since the UNIX epoch        number_of_seconds: how many leap-seconds occur at timestamp    """    fmt = ">4s c 15x 6l"    size = struct.calcsize(fmt)    (tzfile_magic, tzfile_format, ttisgmtcnt, ttisstdcnt, leapcnt, timecnt,        typecnt, charcnt) =  struct.unpack(fmt, f.read(size))    #print("DEBUG: tzfile_magic: {} tzfile_format: {} ttisgmtcnt: {} ttisstdcnt: {} leapcnt: {} timecnt: {} typecnt: {} charcnt: {}".format(tzfile_magic, tzfile_format, ttisgmtcnt, ttisstdcnt, leapcnt, timecnt, typecnt, charcnt))    # Make sure it is a tzfile(5) file    assert tzfile_magic == TZFILE_MAGIC, ( "Not a tzfile; file magic was: '{}'".format(tzfile_magic))    # comments below show struct pres such as "l" for 32-bit long integer    offset = (timecnt*4  # transition times, each "l"        + timecnt*1  # indices tying transition time to ttinfo values, each "B"        + typecnt*6  # ttinfo structs, each stored as "lBB"        + charcnt*1)  # timezone abbreviation chars, each "c"    f.seek(offset, 1) # seek offset bytes from current position    fmt = '>{}l'.format(leapcnt*2)    #print("DEBUG: leapcnt: {}  fmt: '{}'".format(leapcnt, fmt))    size = struct.calcsize(fmt)    data = struct.unpack(fmt, f.read(size))    lst = [(data[i], data[i+1]) for i in range(0, len(data), 2)]    assert all(lst[i][0] < lst[i+1][0] for i in range(len(lst)-1))    assert all(lst[i][1] == lst[i+1][1]-1 for i in range(len(lst)-1))    return lstdef print_leaps(leap_lst):    # leap_lst is tuples: (timestamp, num_leap_seconds)    for ts, num_secs in leap_lst:        print(datetime.datetime.utcfromtimestamp(ts - num_secs+1))if __name__ == '__main__':    import os    zoneinfo_fname = '/usr/share/zoneinfo/right/UTC'    with open(zoneinfo_fname, 'rb') as f:        leap_lst = leap_seconds(f)    print_leaps(leap_lst)