Printing Datetime As Pytz.timezone("etc/gmt-5") Yields Incorrect Result

Consider the following example, where I take a naive datetime, make it timezone aware in UTC, and then convert to UTC-5: d1 = datetime.datetime(2019,3,7, 7,45) d2 = pytz.utc.local

Solution 1:

You are using pytz, not just Python's datetime. Like dateutil, pytz uses the Olson tz database.

The Olson tz database defines Etc/GMT+N timezones which conform with the POSIX style:

those zone names beginning with "Etc/GMT" have their sign reversed from the standard ISO 8601 convention. In the "Etc" area, zones west of GMT have a positive sign and those east have a negative sign in their name (e.g "Etc/GMT-14" is 14 hours ahead of GMT.)

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So, to convert UTC to a timezone with offset -5 you could use Etc/GMT+5:

import datetime as DT
import pytz

naive = DT.datetime(2019, 3, 7, 7, 45)
utc = pytz.utc
gmt5 = pytz.timezone('Etc/GMT+5')
print(utc.localize(naive).astimezone(gmt5))

# 2019-03-07 02:45:00-05:00

Solution 2:

Apparently, in posix style systems, you have to use the inverse of the timezone offset. That means if you want to get -5, you have to use GMT+5.

d3 = d2.astimezone(pytz.timezone('Etc/GMT+5'))

prints

UTC-5:2019-03-07 02:45:00-05:00

Otherwise, you have to pass the posix_offset as true. This is in dateutil documentation;

There is one notable exception, which is that POSIX-style time zones use an inverted offset format, so normally GMT+3 would be parsed as an offset 3 hours behind GMT. The tzstr time zone object will parse this as an offset 3 hours ahead of GMT. If you would like to maintain the POSIX behavior, pass a True value to posix_offset.

https://dateutil.readthedocs.io/en/stable/tz.html#dateutil.tz.tzstr