Problem with timezone conversion when using pytz as tzinfo

[marinellirubens]

Hello, I'm having some problems with timezone conversions from "US/Eastern" to "UTC" but only when using the pytz as tzinfo creating a datetime object.

here is an example:
When I create the date using the timezone as UTC then converted to US/Eastern the conversion is done correctly without any issue, giving me a difference of 4 hour as it should

>>> datetime.datetime(2023, 7, 10, 0, 0, 0, tzinfo=pytz.timezone("UTC")).astimezone(pytz.timezone("US/Eastern"))
datetime.datetime(2023, 7, 9, 20, 0, tzinfo=<DstTzInfo 'US/Eastern' EDT-1 day, 20:00:00 DST>)

But when I do the opposite conversion the calculation is incorrect, adding 56 minutes. as demonstrated below.

>>> datetime.datetime(2023, 7, 9, 20, 0, 0, tzinfo=pytz.timezone("US/Eastern")).astimezone(pytz.timezone("UTC"))
datetime.datetime(2023, 7, 10, 0, 56, tzinfo=<UTC>)

so when the conversion is done in one direction it consider the correct difference 4 hours, but on the other direction if 4:56.

On the other hand if I do the conversion using localize the conversion is done correctly, so there is a problem on the conversion when the object is created using the timezone from pytz (but just when converting to UTC not the opposite)

>>> pytz.timezone("UTC").localize(datetime.datetime(2023, 7, 10, 0, 0)).astimezone(pytz.timezone("US/Eastern"))
datetime.datetime(2023, 7, 9, 20, 0, tzinfo=<DstTzInfo 'US/Eastern' EDT-1 day, 20:00:00 DST>)
>>> pytz.timezone("US/Eastern").localize(datetime.datetime(2023, 7, 9, 20, 0, 0)).astimezone(pytz.timezone('UTC'))
datetime.datetime(2023, 7, 10, 0, 0, tzinfo=<UTC>)

I hope I have given enough information about the error, as I said is possible to do a workaround but would be interesting to correct that.

Thank you.

[krowbar]

See
https://blog.qax.io/pytz-and-strange-timezones/
and
https://stackoverflow.com/questions/24359540/why-doesnt-pytz-localize-produce-a-datetime-object-with-tzinfo-matching-the-t

If you look at the output of
>>> datetime.datetime(2023, 7, 9, 20, 0, 0, tzinfo=pytz.timezone("US/Eastern")) datetime.datetime(2023, 7, 9, 20, 0, tzinfo=<DstTzInfo 'US/Eastern' LMT-1 day, 19:04:00 STD>)

You notice the 'LMT-1 day, 19:04:00 STD' (leading to the missing minutes) compared to

>>> pytz.timezone("US/Eastern").localize(datetime.datetime(2023, 7, 9, 20, 0, 0)) datetime.datetime(2023, 7, 9, 20, 0, tzinfo=<DstTzInfo 'US/Eastern' EDT-1 day, 20:00:00 DST>)
which gives you the correct 'EDT-1 day, 20:00:00 DST'

Using python3.9+ you can use the base zoneinfo.ZoneInfo class as the tzinfo to datetimes.

>>> datetime.datetime(2023, 7, 9, 20, 0, 0, tzinfo=ZoneInfo("US/Eastern")).astimezone(ZoneInfo("UTC")) datetime.datetime(2023, 7, 10, 0, 0, tzinfo=zoneinfo.ZoneInfo(key="UTC"))
>>> datetime.datetime(2023, 7, 10, 0, 0, 0, tzinfo=ZoneInfo("UTC")).astimezone(ZoneInfo("US/Eastern")) datetime.datetime(2023, 7, 9, 20, 0, tzinfo=zoneinfo.ZoneInfo(key='US/Eastern'))