3.6. Datetime Timezone¶
3.6.1. Rationale¶
Always keep dates and times only in UTC (important!)
Datetimes should be converted to local time only when displaying to user
Computerphile Time & Time Zones []
datetime.utcnow()- produces timezone naive date!
Figure 3.1. Comparing datetime works only when all has the same timezone (UTC)¶
Timezone naive datetimes:
from datetime import datetime
datetime(1957, 10, 4, 19, 28, 34)
# datetime.datetime(1957, 10, 4, 19, 28, 34)
datetime.now()
# datetime.datetime(1957, 10, 4, 19, 28, 34)
datetime.utcnow()
# datetime.datetime(1957, 10, 4, 17, 28, 34)
Timezone aware datetime:
from datetime import datetime, timezone
datetime.now(tz=timezone.utc)
# datetime.datetime(1957, 10, 4, 19, 28, 34, tzinfo=datetime.timezone.utc)
datetime(1957, 10, 4, 19, 28, 34, tzinfo=timezone.utc)
# datetime.datetime(1957, 10, 4, 19, 28, 34, tzinfo=datetime.timezone.utc)
dt = datetime(1957, 10, 4, 19, 28, 34)
dt.replace(tzinfo=timezone.utc)
# datetime.datetime(1957, 10, 4, 19, 28, 34, tzinfo=datetime.timezone.utc)
datetime.utcnow(tz=timezone.utc)
# Traceback (most recent call last):
# TypeError: utcnow() takes no keyword arguments
datetime.utcnow(timezone.utc)
# Traceback (most recent call last):
# TypeError: utcnow() takes no arguments (1 given)
3.6.3. Standard Library¶
Since Python 3.9: PEP 615 -- Support for the IANA Time Zone Database in the Standard Library
from zoneinfo import ZoneInfo
from datetime import datetime, timedelta
dt = datetime(2020, 10, 31, 12, tzinfo=ZoneInfo("America/Los_Angeles")) # Daylight saving time
print(dt)
# 2020-10-31 12:00:00-07:00
dt.tzname()
# 'PDT'
dt += timedelta(days=7) # Standard time
print(dt)
# 2020-11-07 12:00:00-08:00
print(dt.tzname())
# PST
3.6.4. pytz¶
pytz brings the Olson tz database into Python:
from pytz import timezone
timezone('UTC')
timezone('US/Eastern')
timezone('Europe/Warsaw')
timezone('Asia/Almaty')
From naive to local time:
from datetime import datetime
from pytz import timezone
my_date = datetime(1969, 7, 21, 2, 56, 15)
timezone('UTC').localize(my_date)
# datetime.datetime(1969, 7, 21, 2, 56, 15, tzinfo=<UTC>)
From naive to local time:
from datetime import datetime
from pytz import timezone
my_date = datetime(1961, 4, 12, 6, 7)
timezone('Asia/Almaty').localize(my_date)
# datetime.datetime(1961, 4, 12, 6, 7, tzinfo=<DstTzInfo 'Asia/Almaty' +06+6:00:00 STD>)
From UTC to local time:
from datetime import datetime
from pytz import timezone
my_date = datetime(1969, 7, 21, 2, 56, 15, tzinfo=timezone('UTC'))
my_date.astimezone(timezone('Europe/Warsaw'))
# datetime.datetime(1969, 7, 21, 3, 56, 15, tzinfo=<DstTzInfo 'Europe/Warsaw' CET+1:00:00 STD>)
Between timezones:
from datetime import datetime
from pytz import timezone
my_date = datetime(1961, 4, 12, 6, 7, tzinfo=timezone('Asia/Almaty'))
my_date.astimezone(timezone('Europe/Warsaw'))
# datetime.datetime(1961, 4, 12, 1, 59, tzinfo=<DstTzInfo 'Europe/Warsaw' CET+1:00:00 STD>)
Descriptor Timezone Converter:
from dataclasses import dataclass
from datetime import datetime
from pytz import timezone
class Timezone:
def __init__(self, name):
self.timezone = timezone(name)
def __get__(self, parent, *args):
return parent.utc.astimezone(self.timezone)
def __set__(self, parent, new_datetime):
local_time = self.timezone.localize(new_datetime)
parent.utc = local_time.astimezone(timezone('UTC'))
@dataclass
class Time:
utc = datetime.now(tz=timezone('UTC'))
warsaw = Timezone('Europe/Warsaw')
moscow = Timezone('Europe/Moscow')
est = Timezone('America/New_York')
pdt = Timezone('America/Los_Angeles')
t = Time()
print('Launch of a first man to space:')
t.moscow = datetime(1961, 4, 12, 9, 6, 59)
print(t.utc) # 1961-04-12 06:06:59+00:00
print(t.warsaw) # 1961-04-12 07:06:59+01:00
print(t.moscow) # 1961-04-12 09:06:59+03:00
print(t.est) # 1961-04-12 01:06:59-05:00
print(t.pdt) # 1961-04-11 22:06:59-08:00
print('First man set foot on a Moon:')
t.warsaw = datetime(1969, 7, 21, 3, 56, 15)
print(t.utc) # 1969-07-21 02:56:15+00:00
print(t.warsaw) # 1969-07-21 03:56:15+01:00
print(t.moscow) # 1969-07-21 05:56:15+03:00
print(t.est) # 1969-07-20 22:56:15-04:00
print(t.pdt) # 1969-07-20 19:56:15-07:00
3.6.5. Assignments¶
"""
* Assignment: Datetime Timezone Define
* Complexity: easy
* Lines of code: 5 lines
* Time: 13 min
English:
1. Use data from "Given" section (see below)
2. Create `timezone` object of:
a. UTC
b. London, United Kingdom
c. Moscow, Russian Federation
d. Warsaw, Poland
e. Tokyo, Japan
f. Sydney, Australia
g. Auckland, New Zealand
h. New York, USA
3. Use `List of tz database time zones` [1]
X. Run doctests - all must succeed
Polish:
1. Użyj danych z sekcji "Given" (patrz poniżej)
2. Stwórz obiekt `timezone` z:
a. UCT
b. London, Wielka Brytania
c. Moscow, Rosja
d. Warsaw, Polska
e. Tokyo, Japan
f. Sydney, Australia
g. Auckland, Nowa Zelandia
h. New York, USA
3. Użyj `List of tz database time zones` [1]
X. Uruchom doctesty - wszystkie muszą się powieść
References:
[1] Wikipedia. List of tz database time zones.
URL: https://en.wikipedia.org/wiki/List_of_tz_database_time_zones
Retrieved: 2021-03-24
[2] IANA. Time Zone Database.
URL: https://data.iana.org/time-zones/releases/
Retrieved: 2021-03-24
Extra Task:
1. Cape Canaveral, FL, USA
2. Houston, TX, USA
3. Bajkonur Cosmodrome, Kazachstan
5. North Pole
6. South Pole (Henryk Arctowski Polish Antarctic Station)
Tests:
>>> import sys; sys.tracebacklimit = 0
>>> from pytz.tzinfo import DstTzInfo, BaseTzInfo
>>> assert isinstance(utc, BaseTzInfo), \
'Variable `utc` has invalid type, must be a BaseTzInfo'
>>> assert isinstance(london, DstTzInfo), \
'Variable `london` has invalid type, must be a DstTzInfo'
>>> assert isinstance(moscow, DstTzInfo), \
'Variable `moscow` has invalid type, must be a DstTzInfo'
>>> assert isinstance(warsaw, DstTzInfo), \
'Variable `warsaw` has invalid type, must be a DstTzInfo'
>>> assert isinstance(tokyo, DstTzInfo), \
'Variable `tokyo` has invalid type, must be a DstTzInfo'
>>> assert isinstance(sydney, DstTzInfo), \
'Variable `sydney` has invalid type, must be a DstTzInfo'
>>> assert isinstance(auckland, DstTzInfo), \
'Variable `auckland` has invalid type, must be a DstTzInfo'
>>> assert isinstance(new_york, DstTzInfo), \
'Variable `new_york` has invalid type, must be a DstTzInfo'
>>> assert isinstance(cape_canaveral, DstTzInfo), \
'Variable `cape_canaveral` has invalid type, must be a DstTzInfo'
>>> assert isinstance(houston, DstTzInfo), \
'Variable `houston` has invalid type, must be a DstTzInfo'
>>> assert isinstance(bajkonur, DstTzInfo), \
'Variable `bajkonur` has invalid type, must be a DstTzInfo'
>>> assert isinstance(north_pole, DstTzInfo), \
'Variable `north_pole` has invalid type, must be a DstTzInfo'
>>> assert isinstance(south_pole, DstTzInfo), \
'Variable `south_pole` has invalid type, must be a DstTzInfo'
>>> utc._utcoffset
datetime.timedelta(0)
>>> london._utcoffset
datetime.timedelta(days=-1, seconds=86340)
>>> moscow._utcoffset
datetime.timedelta(seconds=9000)
>>> warsaw._utcoffset
datetime.timedelta(seconds=5040)
>>> tokyo._utcoffset
datetime.timedelta(seconds=33540)
>>> sydney._utcoffset
datetime.timedelta(seconds=36300)
>>> auckland._utcoffset
datetime.timedelta(seconds=41940)
>>> new_york._utcoffset
datetime.timedelta(days=-1, seconds=68640)
>>> cape_canaveral._utcoffset
datetime.timedelta(days=-1, seconds=68640)
>>> houston._utcoffset
datetime.timedelta(days=-1, seconds=65340)
>>> bajkonur._utcoffset
datetime.timedelta(seconds=18480)
>>> north_pole._utcoffset
datetime.timedelta(seconds=2580)
>>> south_pole._utcoffset
datetime.timedelta(seconds=5040)
"""
# Given
from pytz import timezone
utc: timezone = ... # timezone in UTC
london: timezone = ... # timezone in London, United Kingdom
moscow: timezone = ... # timezone in Moscow, Russian Federation
warsaw: timezone = ... # timezone in Warsaw, Poland
tokyo: timezone = ... # timezone in Tokyo, Japan
sydney: timezone = ... # timezone in Sydney, Australia
auckland: timezone = ... # timezone in Auckland, New Zealand
new_york: timezone = ... # timezone in New York, USA
cape_canaveral: timezone = ... # timezone in Cape Canaveral, FL, USA
houston: timezone = ... # timezone in Houston, TX, USA
bajkonur: timezone = ... # timezone in Bajkonur Cosmodrome, Kazachstan
north_pole: timezone = ... # timezone in North Pole
south_pole: timezone = ... # timezone in South Pole