zoneinfo
— IANA time zone support¶
Nowe w wersji 3.9.
The zoneinfo
module provides a concrete time zone implementation to
support the IANA time zone database as originally specified in PEP 615. By
default, zoneinfo
uses the system’s time zone data if available; if no
system time zone data is available, the library will fall back to using the
first-party tzdata package available on PyPI.
Zobacz także
Using ZoneInfo
¶
ZoneInfo
is a concrete implementation of the datetime.tzinfo
abstract base class, and is intended to be attached to tzinfo
, either via
the constructor, the datetime.replace
method or datetime.astimezone
:
>>> from zoneinfo import ZoneInfo
>>> from datetime import datetime, timedelta
>>> dt = datetime(2020, 10, 31, 12, tzinfo=ZoneInfo("America/Los_Angeles"))
>>> print(dt)
2020-10-31 12:00:00-07:00
>>> dt.tzname()
'PDT'
Datetimes constructed in this way are compatible with datetime arithmetic and handle daylight saving time transitions with no further intervention:
>>> dt_add = dt + timedelta(days=1)
>>> print(dt_add)
2020-11-01 12:00:00-08:00
>>> dt_add.tzname()
'PST'
These time zones also support the fold
attribute
introduced in PEP 495. During offset transitions which induce ambiguous
times (such as a daylight saving time to standard time transition), the offset
from before the transition is used when fold=0
, and the offset after
the transition is used when fold=1
, for example:
>>> dt = datetime(2020, 11, 1, 1, tzinfo=ZoneInfo("America/Los_Angeles"))
>>> print(dt)
2020-11-01 01:00:00-07:00
>>> print(dt.replace(fold=1))
2020-11-01 01:00:00-08:00
When converting from another time zone, the fold will be set to the correct value:
>>> from datetime import timezone
>>> LOS_ANGELES = ZoneInfo("America/Los_Angeles")
>>> dt_utc = datetime(2020, 11, 1, 8, tzinfo=timezone.utc)
>>> # Before the PDT -> PST transition
>>> print(dt_utc.astimezone(LOS_ANGELES))
2020-11-01 01:00:00-07:00
>>> # After the PDT -> PST transition
>>> print((dt_utc + timedelta(hours=1)).astimezone(LOS_ANGELES))
2020-11-01 01:00:00-08:00
Data sources¶
The zoneinfo
module does not directly provide time zone data, and instead
pulls time zone information from the system time zone database or the
first-party PyPI package tzdata, if available. Some systems, including
notably Windows systems, do not have an IANA database available, and so for
projects targeting cross-platform compatibility that require time zone data, it
is recommended to declare a dependency on tzdata. If neither system data nor
tzdata are available, all calls to ZoneInfo
will raise
ZoneInfoNotFoundError
.
Configuring the data sources¶
When ZoneInfo(key)
is called, the constructor first searches the
directories specified in TZPATH
for a file matching key
, and on
failure looks for a match in the tzdata package. This behavior can be
configured in three ways:
The default
TZPATH
when not otherwise specified can be configured at compile time.TZPATH
can be configured using an environment variable.At runtime, the search path can be manipulated using the
reset_tzpath()
function.
Compile-time configuration¶
The default TZPATH
includes several common deployment locations for the
time zone database (except on Windows, where there are no „well-known”
locations for time zone data). On POSIX systems, downstream distributors and
those building Python from source who know where their system
time zone data is deployed may change the default time zone path by specifying
the compile-time option TZPATH
(or, more likely, the configure
flag
--with-tzpath
), which should be a string delimited by os.pathsep
.
On all platforms, the configured value is available as the TZPATH
key in
sysconfig.get_config_var()
.
Environment configuration¶
When initializing TZPATH
(either at import time or whenever
reset_tzpath()
is called with no arguments), the zoneinfo
module will
use the environment variable PYTHONTZPATH
, if it exists, to set the search
path.
-
PYTHONTZPATH
¶ This is an
os.pathsep
-separated string containing the time zone search path to use. It must consist of only absolute rather than relative paths. Relative components specified inPYTHONTZPATH
will not be used, but otherwise the behavior when a relative path is specified is implementation-defined; CPython will raiseInvalidTZPathWarning
, but other implementations are free to silently ignore the erroneous component or raise an exception.
To set the system to ignore the system data and use the tzdata package
instead, set PYTHONTZPATH=""
.
Runtime configuration¶
The TZ search path can also be configured at runtime using the
reset_tzpath()
function. This is generally not an advisable operation,
though it is reasonable to use it in test functions that require the use of a
specific time zone path (or require disabling access to the system time zones).
The ZoneInfo
class¶
-
class
zoneinfo.
ZoneInfo
(key)¶ A concrete
datetime.tzinfo
subclass that represents an IANA time zone specified by the stringkey
. Calls to the primary constructor will always return objects that compare identically; put another way, barring cache invalidation viaZoneInfo.clear_cache()
, for all values ofkey
, the following assertion will always be true:a = ZoneInfo(key) b = ZoneInfo(key) assert a is b
key
must be in the form of a relative, normalized POSIX path, with no up-level references. The constructor will raiseValueError
if a non-conforming key is passed.If no file matching
key
is found, the constructor will raiseZoneInfoNotFoundError
.
The ZoneInfo
class has two alternate constructors:
-
classmethod
ZoneInfo.
from_file
(fobj, /, key=None)¶ Constructs a
ZoneInfo
object from a file-like object returning bytes (e.g. a file opened in binary mode or anio.BytesIO
object). Unlike the primary constructor, this always constructs a new object.The
key
parameter sets the name of the zone for the purposes of__str__()
and__repr__()
.Objects created via this constructor cannot be pickled (see pickling).
-
classmethod
ZoneInfo.
no_cache
(key)¶ An alternate constructor that bypasses the constructor’s cache. It is identical to the primary constructor, but returns a new object on each call. This is most likely to be useful for testing or demonstration purposes, but it can also be used to create a system with a different cache invalidation strategy.
Objects created via this constructor will also bypass the cache of a deserializing process when unpickled.
Ostrzeżenie
Using this constructor may change the semantics of your datetimes in surprising ways, only use it if you know that you need to.
The following class methods are also available:
-
classmethod
ZoneInfo.
clear_cache
(*, only_keys=None)¶ A method for invalidating the cache on the
ZoneInfo
class. If no arguments are passed, all caches are invalidated and the next call to the primary constructor for each key will return a new instance.If an iterable of key names is passed to the
only_keys
parameter, only the specified keys will be removed from the cache. Keys passed toonly_keys
but not found in the cache are ignored.Ostrzeżenie
Invoking this function may change the semantics of datetimes using
ZoneInfo
in surprising ways; this modifies process-wide global state and thus may have wide-ranging effects. Only use it if you know that you need to.
The class has one attribute:
-
ZoneInfo.
key
¶ This is a read-only attribute that returns the value of
key
passed to the constructor, which should be a lookup key in the IANA time zone database (e.g.America/New_York
,Europe/Paris
orAsia/Tokyo
).For zones constructed from file without specifying a
key
parameter, this will be set toNone
.Informacja
Although it is a somewhat common practice to expose these to end users, these values are designed to be primary keys for representing the relevant zones and not necessarily user-facing elements. Projects like CLDR (the Unicode Common Locale Data Repository) can be used to get more user-friendly strings from these keys.
String representations¶
The string representation returned when calling str
on a
ZoneInfo
object defaults to using the ZoneInfo.key
attribute (see
the note on usage in the attribute documentation):
>>> zone = ZoneInfo("Pacific/Kwajalein")
>>> str(zone)
'Pacific/Kwajalein'
>>> dt = datetime(2020, 4, 1, 3, 15, tzinfo=zone)
>>> f"{dt.isoformat()} [{dt.tzinfo}]"
'2020-04-01T03:15:00+12:00 [Pacific/Kwajalein]'
For objects constructed from a file without specifying a key
parameter,
str
falls back to calling repr()
. ZoneInfo
’s repr
is
implementation-defined and not necessarily stable between versions, but it is
guaranteed not to be a valid ZoneInfo
key.
Pickle serialization¶
Rather than serializing all transition data, ZoneInfo
objects are
serialized by key, and ZoneInfo
objects constructed from files (even those
with a value for key
specified) cannot be pickled.
The behavior of a ZoneInfo
file depends on how it was constructed:
ZoneInfo(key)
: When constructed with the primary constructor, aZoneInfo
object is serialized by key, and when deserialized, the deserializing process uses the primary and thus it is expected that these are expected to be the same object as other references to the same time zone. For example, ifeurope_berlin_pkl
is a string containing a pickle constructed fromZoneInfo("Europe/Berlin")
, one would expect the following behavior:>>> a = ZoneInfo("Europe/Berlin") >>> b = pickle.loads(europe_berlin_pkl) >>> a is b True
ZoneInfo.no_cache(key)
: When constructed from the cache-bypassing constructor, theZoneInfo
object is also serialized by key, but when deserialized, the deserializing process uses the cache bypassing constructor. Ifeurope_berlin_pkl_nc
is a string containing a pickle constructed fromZoneInfo.no_cache("Europe/Berlin")
, one would expect the following behavior:>>> a = ZoneInfo("Europe/Berlin") >>> b = pickle.loads(europe_berlin_pkl_nc) >>> a is b False
ZoneInfo.from_file(fobj, /, key=None)
: When constructed from a file, theZoneInfo
object raises an exception on pickling. If an end user wants to pickle aZoneInfo
constructed from a file, it is recommended that they use a wrapper type or a custom serialization function: either serializing by key or storing the contents of the file object and serializing that.
This method of serialization requires that the time zone data for the required
key be available on both the serializing and deserializing side, similar to the
way that references to classes and functions are expected to exist in both the
serializing and deserializing environments. It also means that no guarantees
are made about the consistency of results when unpickling a ZoneInfo
pickled in an environment with a different version of the time zone data.
Zadania¶
-
zoneinfo.
available_timezones
()¶ Get a set containing all the valid keys for IANA time zones available anywhere on the time zone path. This is recalculated on every call to the function.
This function only includes canonical zone names and does not include „special” zones such as those under the
posix/
andright/
directories, or theposixrules
zone.Ostrzeżenie
This function may open a large number of files, as the best way to determine if a file on the time zone path is a valid time zone is to read the „magic string” at the beginning.
Informacja
These values are not designed to be exposed to end-users; for user facing elements, applications should use something like CLDR (the Unicode Common Locale Data Repository) to get more user-friendly strings. See also the cautionary note on
ZoneInfo.key
.
-
zoneinfo.
reset_tzpath
(to=None)¶ Sets or resets the time zone search path (
TZPATH
) for the module. When called with no arguments,TZPATH
is set to the default value.Calling
reset_tzpath
will not invalidate theZoneInfo
cache, and so calls to the primaryZoneInfo
constructor will only use the newTZPATH
in the case of a cache miss.The
to
parameter must be a sequence of strings oros.PathLike
and not a string, all of which must be absolute paths.ValueError
will be raised if something other than an absolute path is passed.
Globals¶
-
zoneinfo.
TZPATH
¶ A read-only sequence representing the time zone search path – when constructing a
ZoneInfo
from a key, the key is joined to each entry in theTZPATH
, and the first file found is used.TZPATH
may contain only absolute paths, never relative paths, regardless of how it is configured.The object that
zoneinfo.TZPATH
points to may change in response to a call toreset_tzpath()
, so it is recommended to usezoneinfo.TZPATH
rather than importingTZPATH
fromzoneinfo
or assigning a long-lived variable tozoneinfo.TZPATH
.For more information on configuring the time zone search path, see Configuring the data sources.
Exceptions and warnings¶
-
exception
zoneinfo.
ZoneInfoNotFoundError
¶ Raised when construction of a
ZoneInfo
object fails because the specified key could not be found on the system. This is a subclass ofKeyError
.
-
exception
zoneinfo.
InvalidTZPathWarning
¶ Raised when
PYTHONTZPATH
contains an invalid component that will be filtered out, such as a relative path.