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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):
for attr, val in zip(self.__slots__, args, strict=True):
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."""
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