zoneinfo — IANA time zone support¶

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.

The ZoneInfo class¶

class zoneinfo.ZoneInfo(key)¶

A concrete datetime.tzinfo subclass that represents an IANA time zone specified by the string key. Calls to the primary constructor will always return objects that compare identically; put another way, barring cache invalidation via ZoneInfo.clear_cache(), for all values of key, 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 raise ValueError if a non-conforming key is passed.

If no file matching key is found, the constructor will raise ZoneInfoNotFoundError.

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 an io.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.

Caution

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 to only_keys but not found in the cache are ignored.

Warning

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 or Asia/Tokyo).

For zones constructed from file without specifying a key parameter, this will be set to None.

Note

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.

>>> 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]'

Functions¶

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/ and right/ directories, or the posixrules zone.

Caution

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.

Note

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 the ZoneInfo cache, and so calls to the primary ZoneInfo constructor will only use the new TZPATH in the case of a cache miss.

The to parameter must be a sequence of strings or os.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 the TZPATH, 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 to reset_tzpath(), so it is recommended to use zoneinfo.TZPATH rather than importing TZPATH from zoneinfo or assigning a long-lived variable to zoneinfo.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 of KeyError.

exception zoneinfo.InvalidTZPathWarning¶

Raised when PYTHONTZPATH contains an invalid component that will be filtered out, such as a relative path.