Python datetime parsing timestamp with timezone

Question

I ran into this problem a while back ago where parsing an ISO string with time zone data and parsing a timestamp (supposedly of the same time) will give different results. I have written a test to check this behavior and it seems pretty inconsistent:

from pytz import timezone as tz
from datetime import datetime

timezone = "Australia/Sydney"
start_time = "2021-05-04T08:12:00"
tz_object = tz(timezone)
naive_datetime = datetime.fromisoformat(start_time)


zoned_time = datetime(naive_datetime.year, naive_datetime.month, naive_datetime.day, naive_datetime.hour, naive_datetime.minute, naive_datetime.second, tzinfo=tz_object)
parsed_time = datetime.fromtimestamp(zoned_time.timestamp(), tz_object)

assert zoned_time.time() == naive_datetime.time()
assert zoned_time.time() == parsed_time.time()

This test produces the following output

  File "test.py", line 13, in <module>
    assert zoned_time.time() == parsed_time.time()
  AssertionError

Unless I'm missing something I can only conclude that the time resulting from this line

parsed_time = datetime.fromtimestamp(zoned_time.timestamp(), tz_object)

Is producing a different time than parsing the actual ISO string. Typically I'd expect the timestamp from the parsed time return a timestamp referring to 8:12 am in the time zone it was assigned.

Is this behavior expected? Did I miss something?

FObersteiner · Accepted Answer · 2021-05-03 06:07:22Z

2

With Python 3.9, use zoneinfo. Note that there is a deprecation shim for pytz if required.

Your code then works fine like

from datetime import datetime
from zoneinfo import ZoneInfo

timezone = "Australia/Sydney"
tz_object = ZoneInfo(timezone)

start_time = "2021-05-04T08:12:00"
naive_datetime = datetime.fromisoformat(start_time)

zoned_time = datetime(naive_datetime.year, naive_datetime.month, naive_datetime.day, naive_datetime.hour, naive_datetime.minute, naive_datetime.second, tzinfo=tz_object)
parsed_time = datetime.fromtimestamp(zoned_time.timestamp(), tz_object)

assert zoned_time.time() == naive_datetime.time()
assert zoned_time.time() == parsed_time.time()

As to why you got an assertion error: with pytz you need to localize the datetime object with the time zone; never set a tzinfo directly with pytz.

answered May 3, 2021 at 6:07

FObersteiner

26.1k9 gold badges60 silver badges94 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Python datetime parsing timestamp with timezone

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related