"tzinfo" objects can be hashable or not depending on the implementation, since "tzinfo" is an abstract base class. In fact, `datetime.timezone.utc` and `datetime.timezone` objects are *already* hashable. There are several reasons why `dateutil` does has not made its tzinfo objects hashable, and they depend on the particular time zone class: 1. `dateutil.tz.tzoffset` is the one that would be easiest to make hashable, /but/ the hashing semantics may not be what you want them to be, because tz.tzoffset("CST", timedelta(hours=-4)) == tz.tzoffset("EDT", timedelta(hours=-4)) returns True. As such those two objects must have the same hash. tz.UTC is a special case of `tz.tzoffset` 2. All the data required to determine if two `dateutil.tz.tzlocal` objects are "the same" is not even available to the Python layer, since `tzlocal` dynamically queries the system time functions whenever you try to resolve an offset with it. This leads to a host of subtle breakages that it may not be possible to fix. It also means `tzlocal` objects are kinda-sorta mutable in some ways. 3. `dateutil.tz.tzfile` and to a lesser extent `dateutil.tz.tzical` both can have a fairly large amount of information backing them. A hash operation that actually uses all this information might be expensive, and one that doesn't use all the information might be wrong. Other than `tz.tzlocal`, these are all fairly surmountable barriers, but honestly I have never seen a particularly /good/ example of a reason to hash tzinfo objects, so I have never felt that it should be a particularly high priority for dateutil. Most of this is basically off-topic for this list, though. On 4/15/19 7:51 PM, Brock Mendel wrote:
This is tied in with the equality semantics of these objects, has come up here, in the dateutil tracker, and in pandas:
https://mail.python.org/archives/list/datetime-sig@python.org/thread/45P3EXY... https://mail.python.org/archives/list/datetime-sig@python.org/thread/45P3EXY... / https://mail.python.org/archives/list/datetime-sig@python.org/thread/45P3EXY...https://github.com/dateutil/dateutil/issues/835 https://github.com/dateutil/dateutil/issues/792 https://github.com/pandas-dev/pandas/pull/24006#discussion_r238483612
My understanding is that hashing cannot be implemented until/unless equality is changed. Is that accurate? Is there a compelling reason for these _not_ to be hashable?
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