import struct def load_tzdata(key): import importlib.resources components = key.split("/") package_name = ".".join(["tzdata.zoneinfo"] + components[:-1]) resource_name = components[-1] try: return importlib.resources.open_binary(package_name, resource_name) except (ImportError, FileNotFoundError, UnicodeEncodeError): # There are three types of exception that can be raised that all amount # to "we cannot find this key": # # ImportError: If package_name doesn't exist (e.g. if tzdata is not # installed, or if there's an error in the folder name like # Amrica/New_York) # FileNotFoundError: If resource_name doesn't exist in the package # (e.g. Europe/Krasnoy) # UnicodeEncodeError: If package_name or resource_name are not UTF-8, # such as keys containing a surrogate character. raise ZoneInfoNotFoundError(f"No time zone found with key {key}") def load_data(fobj): header = _TZifHeader.from_file(fobj) if header.version == 1: time_size = 4 time_type = "l" else: # Version 2+ has 64-bit integer transition times time_size = 8 time_type = "q" # Version 2+ also starts with a Version 1 header and data, which # we need to skip now skip_bytes = ( header.timecnt * 5 # Transition times and types + header.typecnt * 6 # Local time type records + header.charcnt # Time zone designations + header.leapcnt * 8 # Leap second records + header.isstdcnt # Standard/wall indicators + header.isutcnt # UT/local indicators ) fobj.seek(skip_bytes, 1) # Now we need to read the second header, which is not the same # as the first header = _TZifHeader.from_file(fobj) typecnt = header.typecnt timecnt = header.timecnt charcnt = header.charcnt # The data portion starts with timecnt transitions and indices if timecnt: trans_list_utc = struct.unpack( f">{timecnt}{time_type}", fobj.read(timecnt * time_size) ) trans_idx = struct.unpack(f">{timecnt}B", fobj.read(timecnt)) else: trans_list_utc = () trans_idx = () # Read the ttinfo struct, (utoff, isdst, abbrind) if typecnt: utcoff, isdst, abbrind = zip( *(struct.unpack(">lbb", fobj.read(6)) for i in range(typecnt)) ) else: utcoff = () isdst = () abbrind = () # Now read the abbreviations. They are null-terminated strings, indexed # not by position in the array but by position in the unsplit # abbreviation string. I suppose this makes more sense in C, which uses # null to terminate the strings, but it's inconvenient here... abbr_vals = {} abbr_chars = fobj.read(charcnt) def get_abbr(idx): # Gets a string starting at idx and running until the next \x00 # # We cannot pre-populate abbr_vals by splitting on \x00 because there # are some zones that use subsets of longer abbreviations, like so: # # LMT\x00AHST\x00HDT\x00 # # Where the idx to abbr mapping should be: # # {0: "LMT", 4: "AHST", 5: "HST", 9: "HDT"} if idx not in abbr_vals: span_end = abbr_chars.find(b"\x00", idx) abbr_vals[idx] = abbr_chars[idx:span_end].decode() return abbr_vals[idx] abbr = tuple(get_abbr(idx) for idx in abbrind) # The remainder of the file consists of leap seconds (currently unused) and # the standard/wall and ut/local indicators, which are metadata we don't need. # In version 2 files, we need to skip the unnecessary data to get at the TZ string: if header.version >= 2: # Each leap second record has size (time_size + 4) skip_bytes = header.isutcnt + header.isstdcnt + header.leapcnt * 12 fobj.seek(skip_bytes, 1) c = fobj.read(1) # Should be \n assert c == b"\n", c tz_bytes = b"" while (c := fobj.read(1)) != b"\n": tz_bytes += c tz_str = tz_bytes else: tz_str = None return trans_idx, trans_list_utc, utcoff, isdst, abbr, tz_str class _TZifHeader: __slots__ = [ "version", "isutcnt", "isstdcnt", "leapcnt", "timecnt", "typecnt", "charcnt", ] def __init__(self, *args): assert len(self.__slots__) == len(args) for attr, val in zip(self.__slots__, args): setattr(self, attr, val) @classmethod def from_file(cls, stream): # The header starts with a 4-byte "magic" value if stream.read(4) != b"TZif": raise ValueError("Invalid TZif file: magic not found") _version = stream.read(1) if _version == b"\x00": version = 1 else: version = int(_version) stream.read(15) args = (version,) # Slots are defined in the order that the bytes are arranged args = args + struct.unpack(">6l", stream.read(24)) return cls(*args) class ZoneInfoNotFoundError(KeyError): """Exception raised when a ZoneInfo key is not found."""