Python daylight savings time
PythonTimeDstPython Problem Overview
How do I check if daylight saving time is in effect?
Python Solutions
Solution 1 - Python
You can use time.localtime
and look at the tm_isdst
flag in the return value.
>>> import time
>>> time.localtime()
(2010, 5, 21, 21, 48, 51, 4, 141, 0)
>>> _.tm_isdst
0
Using time.localtime()
, you can ask the same question for any arbitrary time to see whether DST would be (or was) in effect for your current time zone.
Solution 2 - Python
The accepted answer is fine if you are running code on your laptop, but most python applications are running on a server using UTC as local time, so they will NEVER be in daylight savings time according to the accepted answer.
The second problem is that different regions implement daylight savings on
different days and times. So even if you have an unambiguous time, such as
datetime.utcnow()
, it could be daylight savings time in one timezone but not
in another.
The best we can do then, is tell whether a given time occurs during DST for a
specific timezone, and the best method I can find for doing it has already
been implemtend by pytz localize
function and we can use it to get a
pretty good answer that works both on our laptop and on a server.
import pytz
from datetime import datetime
def is_dst(dt=None, timezone="UTC"):
if dt is None:
dt = datetime.utcnow()
timezone = pytz.timezone(timezone)
timezone_aware_date = timezone.localize(dt, is_dst=None)
return timezone_aware_date.tzinfo._dst.seconds != 0
Some examples
>>> is_dst() # it is never DST in UTC
False
>>> is_dst(datetime(2019, 1, 1), timezone="US/Pacific")
False
>>> is_dst(datetime(2019, 4, 1), timezone="US/Pacific")
True
>>> is_dst(datetime(2019, 3, 10, 2), timezone="US/Pacific")
NonExistentTimeError
>>> is_dst(datetime(2019, 11, 3, 1), timezone="US/Pacific")
AmbiguousTimeError
In our is_dst
function, we specified is_dst=None
as a parameter to
timezone.localize
, which will cause nonsense times to throw errors. You
could use is_dst=False
to ignore these errors and return False
for those
times.
Solution 3 - Python
Assuming you want to perform this on a datetime
Use pytz
to make it timezone aware and then check its dst
property:
import datetime
import pytz
def is_dst(dt,timeZone):
aware_dt = timeZone.localize(dt)
return aware_dt.dst() != datetime.timedelta(0,0)
timeZone = pytz.timezone("Europe/London")
dt = datetime.datetime(2019,8,2)
is_dst(dt,timeZone)
True
dt = datetime.datetime(2019,2,2)
is_dst(dt,timeZone)
False
Solution 4 - Python
None of the above helped me so I found my own workaround.
I relate to the logic implemented in https://gist.github.com/dpapathanasiou/09bd2885813038d7d3eb while there's still a problem, it doesn't work in real life apparently :(
Currently I'm in Israel and here we move the clock in the end of the month,
while in Australia they have already moved the clock.
All the codes return True
for both Asia/Jerusalem
and Australia/Sydney
.
Eventually I used an external 3rd party API - https://worldtimeapi.org/ - by which I analyse whether the utc_offset
is 11 hours (rather that 10:05).
from requests import get as Get
is_dst = True
try:
tz_check = Get('https://worldtimeapi.org/api/timezone/Australia/Sydney')
is_dst = tz_check.json().get('utc_offset') == '+11:00'
except Exception as e:
print('!!! Error getting timezone', e)
I agree this is a private case, but I hope this can help someone :)
Solution 5 - Python
I would have posted this as a comment to the answer by @mehtunguh above, but my current reputation level does not allow me to comment.
I think there may be an issue with the is_dst
function as written when the dt
argument is omitted.
When the dt
argument is omitted, dt
is set to datetime.utcnow()
which returns a naive datetime representing the current UTC time. When that is passed to pytz.localize
, the resulting localized time is not the current time in the specified time zone, but rather the local time that has the same hour, minute, second, as the current UTC time.
So, for example, as I write this it is 10:50 AM EST in the US/Eastern time zone, and datetime.utcnow()
returns a datetime value with hour=15
and minute=50
. As written, when invoked as is_dst(timezone='US/Eastern')
, is_dst
is not checking whether the current local time of 10:50 AM EST is during daylight saving time, it is checking whether 3:50 PM EST is during daylight saving time.
I think is_dst
should perhaps be coded as follows:
import datetime
import pytz
def is_dst(dt=None, timezone='UTC'):
timezone = pytz.timezone(timezone)
if dt is None:
dt = datetime.datetime.now(datetime.timezone.utc)
if dt.tzinfo is None:
tz_aware_dt = timezone.localize(dt, is_dst=None)
else:
tz_aware_dt = dt.astimezone(timezone)
return tz_aware_dt.tzinfo._dst.seconds != 0
This version allows passing either a naive datetime value or a timezone-aware datetime value as the dt
argument. When the dt
argument is omitted, it uses a timezone-aware version of the current UTC time so that when that gets localized to the specified timezone it represents the current time in that timezone.
Solution 6 - Python
Expanding @Greg Hewgill's answer above, plus coping with local timezone (with help of pip install tzlocal
), you get:
import time
from datetime import datetime, timedelta
from tzlocal import get_localzone
def to_local(dt):
"""From any timezone to local datetime - also cope with DST"""
localtime = time.localtime()
if localtime.tm_isdst:
utctime = time.gmtime()
hours_delta = timedelta(hours=(localtime.tm_hour - utctime.tm_hour))
dt = dt - hours_delta
return dt.replace(tzinfo=get_localzone())
Solution 7 - Python
I'm from the UK and this is how I handled my server returning the wrong time for half the year:
import pytz
from typing import Optional
from datetime import datetime
class BritishTime(datetime):
timezone = pytz.timezone('Europe/London')
@classmethod
def dst(cls, dt: Optional[datetime] = None):
dt = dt if dt is not None else cls.now()
return cls.timezone.dst(dt)
Now if I create a datetime object with BritishTime
, it has the dst
method which I can use to both check and update the time, something like this:
def get_correct_time(timestamp):
updated = BritishTime.fromtimestamp(timestamp)
return updated + updated.dst()
Works pretty well.