How to compute the time difference between two time zones in python?

Question

How can I compute the time differential between two time zones in Python? That is, I don't want to compare TZ-aware datetime objects and get a timedelta; I want to compare two TimeZone objects and get an offset_hours. Nothing in the datetime library handles this, and neither does pytz.

Answer 1

from datetime import datetime
from zoneinfo import ZoneInfo

dt = datetime.now() # 2020-09-13
tz0, tz1 = "Europe/Berlin", "US/Eastern" # +2 vs. -4 hours rel. to UTC

utcoff0, utcoff1 = dt.astimezone(ZoneInfo(tz0)).utcoffset(), dt.astimezone(ZoneInfo(tz1)).utcoffset()

print(f"hours offset between {tz0} -> {tz1} timezones: {(utcoff1-utcoff0).total_seconds()/3600}")
>>> hours offset between Europe/Berlin -> US/Eastern timezones: -6.0

• a way to do this with Python 3.9's standard library.

Answer 2

Here is a solution using the Python library Pytz which solves the issue of ambiguous times at the end of daylight saving time.

from pytz import timezone
import pandas as pd

def tz_diff(date, tz1, tz2):
    '''
    Returns the difference in hours between timezone1 and timezone2
    for a given date.
    '''
    date = pd.to_datetime(date)
    return (tz1.localize(date) - 
            tz2.localize(date).astimezone(tz1))\
            .seconds/3600

The examples below calculate the difference in hours between UTC and Australia time for the first of January and first of June respectively. Notice how daylight savings are taken into consideration.

utc = timezone('UTC')
aus = timezone('Australia/Sydney')

tz_diff('2017-01-01', utc, aus)

# 11.0

tz_diff('2017-06-01', utc, aus)

# 10.0

Thanks