timezones in python

timezones python.py

# working with timezones
from datetime import datetime
# pytz is required for timezone aware datetime and time objects
import pytz


# help function
def checkAwareness(dt):
    if dt.tzinfo is None:
        print(f'datetime is naive (tzinfo is {dt.tzinfo})')
    else:
        print(f'datetime is aware (tzinfo is {dt.tzinfo})')

# obtain the current time (it is naive, i.e. it is not timezone aware)
now = datetime.now()
print(f'now time is {now}')
checkAwareness(now)

# example 1: make datetime object timezone aware
timezone = pytz.timezone('Europe/Helsinki')
now_aware = timezone.localize(now)
print(f'now aware time is {now_aware}')
checkAwareness(now_aware)

# example 2: best practice:
#            - use aware datetime objects
#            - work with UTC time and convert to desired timezone at the end
now_utc = datetime.utcnow()
print(f'UTC time is {now_utc}')
checkAwareness(now_utc)
# set the timezone as UTC
timezone = pytz.timezone('UTC')
now_utc_aware = timezone.localize(now_utc)
print(f'UTC aware time is {now_utc_aware}')
checkAwareness(now_utc_aware)
# obtain the time in Helsinki
now_Helsinki_aware = now_utc_aware.astimezone(pytz.timezone('Europe/Helsinki'))
print(f'Helsinki aware time is {now_Helsinki_aware}')
checkAwareness(now_Helsinki_aware)

# output
# now time is 2019-11-17 16:23:43.040856
# datetime is naive (tzinfo is None)
# now aware time is 2019-11-17 16:23:43.040856+02:00
# datetime is aware (tzinfo is Europe/Helsinki)

# UTC time is 2019-11-17 14:23:43.040856
# datetime is naive (tzinfo is None)
# UTC aware time is 2019-11-17 14:23:43.040856+00:00
# datetime is aware (tzinfo is UTC)
# Helsinki aware time is 2019-11-17 16:23:43.040856+02:00
# datetime is aware (tzinfo is Europe/Helsinki)