`zoneinfo` — IANA time zone support¶

Added in version 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.

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 in PYTHONTZPATH will not be used, but otherwise the behavior when a relative path is specified is implementation-defined; CPython will raise InvalidTZPathWarning, 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 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(file_obj, /, 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__()

🔥 HOT: /library/zoneinfo.html - Collection

zoneinfo — IANA time zone support¶

Using ZoneInfo¶