Taragolis commented on PR #34492:
URL: https://github.com/apache/airflow/pull/34492#issuecomment-1728301574
> maybe we should see a first iteration and then figure out if we want to
support non-pendulum timezone aware datetimes. I do not think we should, due to
all the issues with the other implementations, but open to discussion.
I'm just worry, if we only would serialize `datetime.datetime` and
`pendulum.DataTime` with pendulum Timezone, then we potentially could breaks
someone pipeline, because right now it is possible without any issues serialize
datetime with UTC timezone regardless of `tzinfo` implementation. And different
libraries use different `tzinfo` for timezones, for example
- boto3: python-dateutils
- psycopg2: own implementation
- psycopg (formally v3): zoneinfo.ZoneInfo and
backports.zoneinfo.ZoneInfo(Python < 3.9)
In general you could compare `datetime.datetime` with different `tzinfo`
implementation
```python
from dateutil.tz import tzutc
from datetime import datetime, timezone, timedelta
from pendulum.tz.timezone import Timezone
from zoneinfo import ZoneInfo
from pendulum.tz import timezone as ptimezone
from psycopg2.tz import FixedOffsetTimezone
from pytz import UTC
d1 = datetime(2021, 1, 1, tzinfo=timezone.utc)
d2 = datetime(2021, 1, 1, tzinfo=Timezone("UTC"))
d3 = datetime(2021, 1, 1, tzinfo=tzutc())
d4 = datetime(2021, 1, 1, tzinfo=ZoneInfo("UTC"))
d5 = datetime(2021, 1, 1, tzinfo=FixedOffsetTimezone(offset=0))
d6 = datetime(2021, 1, 1, tzinfo=UTC)
assert d1 == d2 == d3 == d4 == d5 == d6
assert d1.tzname() == d2.tzname() == d3.tzname() == d4.tzname() ==
d6.tzname()
assert d5.tzname() == "+00" # psycopg2 uses Python 2.3 implementation ;-)
assert d1.utcoffset() == d2.utcoffset()
assert d1.utcoffset() == d3.utcoffset()
assert d1.utcoffset() == d4.utcoffset()
assert d1.utcoffset() == d5.utcoffset()
assert d1.utcoffset() == d6.utcoffset()
dl1 = datetime(2021, 6, 1, tzinfo=Timezone("Europe/London"))
dl2 = datetime(2021, 6, 1, tzinfo=ZoneInfo("Europe/London"))
dl3 = datetime(2021, 6, 1, tzinfo=timezone(timedelta(hours=1)))
assert dl1 == dl2 == dl3
dl1_from_name = datetime(2021, 6, 1, tzinfo=ptimezone(dl1.tzinfo.name))
dl1_from_offset = datetime(2021, 6, 1,
tzinfo=ptimezone(int(dl1.utcoffset().total_seconds())))
assert dl1 == dl1_from_name == dl1_from_offset
dl2_from_name = datetime(2021, 6, 1, tzinfo=ptimezone(dl2.tzinfo.key))
dl2_from_offset = datetime(2021, 6, 1,
tzinfo=ptimezone(int(dl2.utcoffset().total_seconds())))
assert dl2 == dl2_from_name == dl2_from_offset
dl3_from_offset = datetime(2021, 6, 1,
tzinfo=ptimezone(int(dl3.utcoffset().total_seconds())))
assert dl3 == dl3_from_offset
```
Maybe we should try to serialize `datetime.datetime` but result of
deserialization will always use Pendulum timezone regardless original one.
In case of serialize just timezone I think it is fine to serialize only
Pendulum one, and when we have min Python 3.9 we could discuss should we also
serialize `zoneinfo.ZoneInfo`
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