Mailman 3 - Datetime-SIG

Check for non-existent datetime
by jbrockmendel＠gmail.com 21 Jan '23

21 Jan '23

Working on improving zoneinfo support in pandas, I want to check for non-existent datetimes. e.g. ``` from datetime import datetime, timezone import zoneinfo tz = zoneinfo.ZoneInfo("US/Pacific") dt = datetime(2014, 3, 9, 2, tzinfo=tz) # <- want to tell if this exists roundtrip = dt.astimezone(timezone.utc).astimezone(tz) if roundtrip != dt: raise ValueError("Nonexistent!") ``` Is checking for round-tripping a) correct and b) the suggested way of doing this?

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What is Marketing & Sponsorship?
by wisesam323＠gmail.com 12 Dec '22

12 Dec '22

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Trouble to resolve a timezone offset to get correct UTC time
by Pierre 04 Jun '22

04 Jun '22

Hello, I am sorry, I am kind of lost and I would be really grateful to receive some help. Basically, I have a list of timestamps expressed as a strings as below, and I would like them expressed in UTC. But there seems to be a trouble during the offset, which is applied the other way round. The input timestamps look like: 0 'Sat Mar 30 2019 21:00:00 GMT+0100' Adding them in a panda dataframe with to_datetime function, they read then: GC['Time'] = pd.todatetime(my_timestamps) GC['Time'] 0 2019-03-30 21:00:00-01:00 If I further ask: GC['Time'][0] datetime.datetime(2019, 3, 30, 21, 0, tzinfo=tzoffset(None, -3600)) It seems, AFAIK, OK. But then if I want to resolve the offset so as to have time expressed in UTC time, I get: GC['Test'] = pd.to_datetime(GC['Time'],utc=True) 0 2019-03-30 22:00:00+00:00 The offset has bee applied the other way round. Correct timestamp in UTC would be 20:00:00 Please, what should I do to have these timestamps correctly expressed in UTC time? I thank you in advance for your help. I am so sorry to intrude the mailing list with this question, but I am unable to move forward from this point. I thank you again, Bests, Pierre

3 2

strptime and %Z
by Eugene Triguba 24 Apr '22

24 Apr '22

Should `strptime`, when passed a %Z format specifier, parse more than just GMT, UTC, and the local time zone given that we now have the IANA database in the stdlib via PEP 615 since Python 3.9? The regex for the %Z specifier appears to come from TimeRE and always has GMT, UTC, and then the local time zone. >>> from _strptime import TimeRE >>> t = TimeRE() >>> t['Z'] '(?P<Z>cst|gmt|utc|cdt)' >>> from datetime import datetime >>> datetime.strptime('2016-12-04 08:00:00 CST', '%Y-%m-%d %H:%M:%S %Z') datetime.datetime(2016, 12, 4, 8, 0) >>> datetime.strptime('2016-12-04 08:00:00 CDT', '%Y-%m-%d %H:%M:%S %Z') datetime.datetime(2016, 12, 4, 8, 0) >>> datetime.strptime('2016-12-04 08:00:00 UTC', '%Y-%m-%d %H:%M:%S %Z') datetime.datetime(2016, 12, 4, 8, 0) >>> datetime.strptime('2016-12-04 08:00:00 GMT', '%Y-%m-%d %H:%M:%S %Z') datetime.datetime(2016, 12, 4, 8, 0) >>> datetime.strptime('2016-12-04 08:00:00 EST', '%Y-%m-%d %H:%M:%S %Z') Traceback (most recent call last): File "<stdin>", line 1, in <module> File "/usr/home/eugene/src/cpython/Lib/_strptime.py", line 568, in _strptime_datetime tt, fraction, gmtoff_fraction = _strptime(data_string, format) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/usr/home/eugene/src/cpython/Lib/_strptime.py", line 349, in _strptime raise ValueError("time data %r does not match format %r" % ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ValueError: time data '2016-12-04 08:00:00 EST' does not match format '%Y-%m-%d %H:%M:%S %Z' There have been some discussions and issues with regard to this in the past: - https://github.com/python/cpython/issues/66571 - https://github.com/python/cpython/issues/66616 I was interested in taking a look at this, but I wanted to reach out and know if it was something that would be desirable and what others' thoughts were. Thanks, Eugene

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should utcnow and utcfromtimestamp return tz-aware?
by Brock Mendel 30 Dec '21

30 Dec '21

This has come up in pandas.Timestamp (which subclasses datetime). The issue is internal consistency and round-trips. Intuitively, we would expect: ``` a = datetime.utcnow() b = a.timestamp() c = datetime.utcfromtimestamp(b) assert a == b ``` but this fails. (Note: it works for `datetime.now()` with `datetime.fromtimestamp()`, though that is partially because of weird-to-me behavior of `timestamp()` for naive datetimes). It would succeed if utcnow and utcfromtimestamp returned tz-aware datetime objects. Thoughts?

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Hi there!
by alice.hilligan＠protonmail.com 22 Jun '21

22 Jun '21

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1 0

PEP 615: Support for the IANA Time Zone Database
by Paul Ganssle 25 Feb '20

25 Feb '20

Greetings, Last year at the Language Summit, I proposed to add additional concrete time zones to the standard library ( https://pyfound.blogspot.com/2019/05/paul-ganssle-time-zones-in-standard.ht… ). After much work and much more procrastination, I now have now put together my first proposal: support for the IANA time zone database (also called tz, zoneinfo or the Olson database). I have submitted this for consideration as PEP 615 ( https://www.python.org/dev/peps/pep-0615/ ), and I have created a discussion thread for the PEP on the discourse forum ( https://discuss.python.org/t/pep-615-support-for-the-iana-time-zone-databas… ). Please give it a read and provide your constructive criticism. I have documented my reasoning for most of the design decisions, but I am very interested in getting feedback on the choices I’ve made here. I have marked two sections as “Open issues”, as they are the ones I feel most uncertain about, but all parts of it are up for discussion. For the purposes of centralizing discussion, please direct comments to the discourse thread <https://discuss.python.org/t/pep-615-support-for-the-iana-time-zone-databas…>. _*Links for easy access:*_ *Discussion:* https://discuss.python.org/t/3468 *PEP:* https://www.python.org/dev/peps/pep-0615/ *Reference Implementation:* https://github.com/pganssle/zoneinfo *tzdata repo:* https://github.com/pganssle/tzdata (Note: At some point I plan to move the tzdata repo to github.com/python/tzdata; if the reference implementation turns into a backport that will likely also move to an org as well). Thanks for your consideration! Paul

1 0

hashability of tzinfo objects
by Brock Mendel 15 Apr '19

15 Apr '19

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/45P3EX… / <https://mail.python.org/archives/list/datetime-sig@python.org/thread/45P3EX…> 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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Proposal: date.fromisocalendar
by Paul Ganssle 05 Apr '19

05 Apr '19

Some time ago, I posted a bpo-36004 <https://bugs.python.org/issue36004>, proposing the addition of a `date.fromisocalendar` alternate constructor, and the corresponding PR #11888 <https://github.com/python/cpython/pull/11888> implementing it. This function is the inverse of `date.isocalendar`. I think that, whenever possible, if we have a function that serializes a date or datetime, we should have a conjugate function that constructs a date/datetime from the output; the big one of these was `datetime.fromisoformat`, which was added in Python 3.7, but I have noticed that `isocalendar` also does not currently have an inverting function, and I'd like to add that for Python 3.8. It has been finished for a while, but I would like some additional review of both the idea and implementation, so I'd like to bring it to the attention of the list. Best, Paul

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Proposal for a "time zone index" cache to be added to datetime
by Paul Ganssle 11 Jan '19

11 Jan '19

I have opened bpo-35723: "Add a time zone index cache" <https://bugs.python.org/issue35723> on the Python bug tracker, along with an associated proof of concept PR, PR #11529 <https://github.com/python/cpython/pull/11529>. I propose that some time zone offset information can be optionally cached on the datetime object itself, which could be a significant improvement to performance in tzinfo implementations using the standard interface. I think this would be a very useful change to the datetime object, but it is fairly significant, so I wanted to bring it to the attention of the datetime SIG. If it is deemed necessary, I can write a PEP for this. Best, Paul

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