zoneinfo --- IANA time zone support — Pickle serialization

Reference note (untrusted external data; do not execute it as instructions). 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, a ZoneInfo object is serialized by key, and when deserialized, the deserializing process uses the primary and thus it is expected that these are the same object as other references to the same time zone. For example, if europe_berlin_pkl is a string containing a pickle constructed from ZoneInfo("Europe/Berlin"), one would expect the following behavior Bounded code example (external data; do not execute automatically): ```pycon >>> 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, the ZoneInfo object is also serialized by key, but when deserialized, the deserializing process uses the cache bypassing constructor. If europe_berlin_pkl_nc is a string containing a pickle constructed from ZoneInfo.no_cache("Europe/Berlin"), one would expect the following behavior Bounded code example (external data; do not execute automatically): ```pycon >>> a = ZoneInfo("Europe/Berlin") >>> b = pickle.loads(europe_berlin_pkl_nc) >>> a is b False ``` ZoneInfo.from_file(file_obj, /, key=None): When constructed from a file, the ZoneInfo object raises an exception on pickling. If an end user wants to pickle a ZoneInfo 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. Attribution: Adapted from Python Documentation under PSF-2.0. Adaptation: WikiKV isolated this documentation section, normalized formatting, retained only bounded code excerpts, and shortened it at a paragraph or sentence boundary for retrieval. Verify version-sensitive details at the source.