Using Python datetime with Timezones

Links

• https://vinta.ws/code/timezone-in-python-offset-naive-and-offset-aware-datetimes.html

Distinguishing between TZ Aware and TZ Naive Objects

from datetime import datetime

now = datetime.now()
 
now = now.replace(tzinfo=datetime.timezone.utc)

if now.tzinfo == None or \
   now.tzinfo.utcoffset(now) == None:
    # If these conditions are met the object is unaware
    print("Unaware")
else:
    print("Aware")

print(now.isoformat())

Binding with Timezone Info

cat !$
cat ./py_tz_example_01.py
#!/usr/bin/env python3

import pytz 

from datetime import datetime 

def list_tz():
    for tz in pytz.all_timezones:
        print(tz)


def example(tz_name):

    specified_tz = pytz.timezone(tz_name)

    # transform to a time using a specific timezone 

    tz_aware_dt = datetime.now(tz=specified_tz)

    print(f"TZ aware datetime value |{tz_aware_dt.isoformat()}| for timezone - '{tz_name}'")


# list_tz()

print(f"TZ naive datetime value |{datetime.now().isoformat()}|")

example("America/New_York")
example("America/Vancouver")
example("Asia/Tokyo")
example("Australia/Sydney")
example("Europe/London")
example("Europe/Paris")

Output

% ./py_tz_example_01.py    
TZ naive datetime value |2022-06-05T09:48:41.237251|
TZ aware datetime value |2022-06-04T19:48:41.249310-04:00| for timezone - 'America/New_York'
TZ aware datetime value |2022-06-04T16:48:41.249630-07:00| for timezone - 'America/Vancouver'
TZ aware datetime value |2022-06-05T08:48:41.249701+09:00| for timezone - 'Asia/Tokyo'
TZ aware datetime value |2022-06-05T09:48:41.249923+10:00| for timezone - 'Australia/Sydney'
TZ aware datetime value |2022-06-05T00:48:41.250303+01:00| for timezone - 'Europe/London'
TZ aware datetime value |2022-06-05T01:48:41.250543+02:00| for timezone - 'Europe/Paris'

Explicit Numerical Offsets from UTC

#!/usr/bin/env python3

from datetime import datetime, timezone

dt = datetime.now()

# This is a naive datetime value

print(f" TZ naive datetime value |{dt.isoformat()}|")
print(f"               dt.tzinfo |{dt.tzinfo}|")

# Cast this as UTC

dt = dt.replace(tzinfo=timezone.utc)

# Define the offset

offset = "+1000"  # "Australia/Melbourne"

# Convert as so...

tz_aware_dt = dt.astimezone(datetime.strptime(offset, "%z").tzinfo)

print(f" TZ Aware datetime value |{tz_aware_dt.isoformat()}|")

Output

% ./py_tz_example_02.py
 TZ naive datetime value |2022-06-05T09:49:37.782118|
               dt.tzinfo |None|
 TZ Aware datetime value |2022-06-05T19:49:37.782118+10:00|

Changing Timezones

from pytz import timezone
from datetime import datetime

fmt = "%Y-%m-%d %H:%M:%S %Z%z"

# Current datetime in UTC

dt = datetime.now(timezone('UTC'))

print(dt.strftime(fmt))

# Convert to US/Pacific time zone

dt = dt.astimezone(timezone('Asia/Tokyo'))

print(dt.strftime(fmt))

# Convert to Europe/Paris time zone

dt = dt.astimezone(timezone('Europe/Paris'))

print dt.strftime(fmt)

Output

./tst_ft.py
2022-06-05 09:41:02 UTC+0000
2022-06-05 18:41:02 JST+0900
2022-06-05 11:41:02 CEST+0200

Show System Timezone

import tzlocal

tzlocal.get_localzone()
# <DstTzInfo 'Asia/Taipei' LMT+8:06:00 STD>

tzlocal.get_localzone().zone
# 'Asia/Taipei'

from time import gmtime, strftime
print(strftime("%z", gmtime()))
# +0800

Find Timezones Of A Certain Country

import pytz

pytz.country_timezones('tw')
# ['Asia/Taipei']

pytz.country_timezones('cn')
# ['Asia/Shanghai', 'Asia/Urumqi']

Other Examples

Since dateutil uses the same timezone model as the datetime lib, you can set the tzinfo property straight away. You can also use .replace(tzinfo=...) safely.

import dateutil

aware_datetime = datetime(2020, 1, 5, 10, 12, tzinfo=dateutil.tz.gettz('Europe/London'))

print(aware_datetime)

# 2020-01-05 10:12:00+00:00

By the way, the procedure is identical if you use the zoneinfo module on Python 3.9:

from zoneinfo import ZoneInfo

aware_datetime = datetime(2020, 1, 5, 10, 12, tzinfo=ZoneInfo('Europe/London'))